Class 10 Physical Science

Organic Chemistry Topic A General Properties Of Organic Compounds Synopsis

WBBSE Class 10 Organic Chemistry Overview

1. In 1828, a German chemist Friedrich Wohler synthetically prepared urea, an organic compound found in the urine of most mammals, by heating an inorganic compound, ammonium .cyanate. This accidental synthesis gave a fatal blow to the ‘vital force theory’ in which it was considered impossible to prepare an organic compound in the laboratory from inorganic compounds.

2. The fundamental element of all organic compounds is carbon. Apart from carbon, H, O, N, S, P, halogens and some metals may also be present in organic compounds.
3. The self-linking property of carbon by virtue of which its atoms mutually combine with each other to form long open chains (straight or branched) and rings is called catenation. Using its catenation property, carbon forms a vast number of organic compounds.
4. Organic compounds in which all the adjacent carbon atoms are linked to one another by single bonds only are called saturated compounds. For example, methane, ethane.

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5. Organic compounds which contain at least one carbon-carbon double bond or triple bond are called unsaturated compounds. For example, ethylene, and acetylene.
6. Organic compounds containing carbon and hydrogen are called hydrocarbons.
7. An atom or a group of atoms present in an organic compound, which determines the nature and characteristic chemical properties of the compound is called a functional group.

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8. The phenomenon of existence of two or more compounds possessing the same molecular formula but different physical and chemical properties is called isomerism. Such compounds showing isomersim are called isomers.
9. The compounds having the same molecular formula but different structures are called structural isomers and the phenomenon is known as structural isomerism.

10. Structural isomerism may arise due to differences in functional groups or positions of the functional groups in the carbon chain.

ch₃ch₂ch₂oh Iupac Name

Example of functional group isomerism:

CH₃ — O — CH₃ (dimethyl ether)
CH₃ —  CH₂ — OH (ethanol)

Example of positional isomerism:

CH₃CH₂CH₂OH (propan-1-ol)

CH₃ — CH(OH) — CH₃ (propan-2-ol)

11. A homologous series may be defined as a series or group of similarly constituted organic compounds having same functional group and same general formula arranged in increasing order of molecular mass. Any two successive members of a homologous series differ in their molecular formula by ‘a’ CH₂ group or unit. The members of a homologous series are called homologues.

CH₃CH₂CH₂OH Iupac Name

12. General formula of the homologous series of alkanes is C_nH_{2n + 2} and the general formulae of alkene and alkyne are C_nH_2n-2 and C_nH_2n respectively.
13. A scientific and systematic approach of naming the organic compounds was adopted in a conference attended by chemists from worldwide. These rules of naming organic compounds are collectively known as IUPAC (International Union of Pure and Applied Chemistry) nomenclature of organic compounds. These rules have been modified from time to time.

Organic Chemistry Topic A General Properties Of Organic Compounds Short And Long Answer Type Questions

Question 1. Write three differences between organic and inorganic compounds.

Answer:

The major differences between organic and inorganic compounds are as follows:

Property	Organic compound	Inorganic compound
1. Constituents	All organic compounds must contain carbon. Apart from carbon, elements like H, N, 0, S, P, halogens etc., may also be present in organic compounds. Existence of more than 20 lakhs of organic compounds is known till date.	Inorganic compounds may or may not contain carbon. About 92 naturally occurring elements and some synthetically prepared elements form almost 90000 inorganic compounds which is far less than the number of organic compounds.
2. Melting point and boiling point	Organic compounds being covalent in nature generally have low melting and boiling points.	Most inorganic compounds being ionic in nature have high melting and boiling points.
3. Solubility	Organic compounds are soluble in organic and non-polar solvents like benzene, CCI4 etc., but insoluble in polar solvents such as water.	Inorganic compounds are generally soluble in polar solvents such as water but insoluble in non-polar solvents such as benzene.

 

Question 2. The general molecular formula isomers is C₄H₈. Predict the structural formula of those compounds.

Answer:

The general molecular formula of the isomers is C4H8. The formula conforms to the general formula CnH2n (where n = 4) which belongs to the alkene family.

Therefore, the possible isomers and their structural formulas are as follows:

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Question 3. What is homologous series? Discuss the significance of homologous series.

Answer:

Homologous series

1. A homologous series may be defined as a series or a group of similarly constituted organic compounds having the same functional group and general formula arranged in order of their increasing molecular mass. Any two successive members of a homologous series differ in their molecular formula by a CH₂ -group or unit. The members of a homologous series are called homologues.

The significance of homologous series

2. If the method of preparation and properties of a certain member of a homologous series are known, then the method of preparation and properties of the other members of the same series can be easily predicted.

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Question 4. Mention the important characteristics of a homologous series.

Answer:

The important characteristics of a homologous series

1. All the members of a homologous series have the same constituent elements and they can be represented by a single general formula.
2. If all the members of a homologous series are arranged in increasing order of their molecular masses, then two consecutive members of the family differ from one-another by one CH₂ -group and the difference in their molecular mass is 14 units.
3. All the members of a homologous series have almost similar chemical properties.

Question 5. How was Berzelius’ ‘vital force theory’ proved invalid?

Answer: In 1828, scientist Wohler accidentally prepared urea, an organic compound, by heating an inorganic compound, ammonium cyanate. Later, in 1845, Kolbe and in 1856, Berthelot prepared acetic acid and methane respectively from their constituent elements in the laboratory.

All these discoveries proved that no vital force inherent to living beings was involved in the formation of organic compounds. Thus, the ‘vital force theory’ was proved invalid.

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Question 6. Why are organic compounds generally insoluble in water (a polar solvent)?

Answer: As organic compounds are formed by covalent bonds, they do not dissociate or ionise in water or any other polar solvents. Consequently, no electrostatic force of attraction develops between the water molecules and the molecules of the organic compound.

So, organic compounds are insoluble in water. However, some organic compounds dissolve in water by forming hydrogen bonds with water molecules (such as alcohols, glucose etc.) or by ionising in water (such as carboxylic acids).

Question 7. Why are the solutions of organic compounds generally non-conductor of electricity?

Answer: As organic compounds are formed by covalent bonds, they do not ionise in water or any other polar solvents. Hence, they cannot conduct electricity in solutions. However, aqueous solutions of carboxylic acids such as formic acid, acetic acid etc., ionise in water and conduct electricity to a small extent.

Understanding Organic Compounds and Their Properties

Question 8. What is the catenation property of carbon?

Answer:

The catenation property of carbon

The unique self-linking property of carbon due to which C-atoms mutually combine with each other by forming covalent single, double or triple bonds to form long open chains (straight or branched) and rings of different sizes is called catenation property of carbon. Due to this reason, carbon forms a vast number of organic compounds.

 

 

Question 9. Why is carbon able to show catenation property?

Answer: Due to the small size and moderate electronegativity of carbon atoms, it can form very strong and stable carbon-carbon covalent bonds. As a result, carbon atoms can link with one another by forming covalent single, double or triple bonds. For these reasons, carbon is able to show catenation property which leads to the formation of a large number of open chain and cyclic compounds.

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Question 10. Briefly describe the tetrahedral model of the four valencies (bonds) of carbon as proposed by scientists van’t Hoff and Le Bel.

Answer: In 1874, scientists van’t Hoff and Le Bel proposed the tetrahedral model of the four valencies of carbon. According to this model—

1. All four valencies of a carbon atom cannot be on the same plane.
2. If a carbon atom is placed at the centre of an imaginary regular tetrahedron, then the four valencies of the C-atom will be directed towards the four corners of the tetrahedron.
3. The angle between any two valencies of the carbon atom is 109°28′.

 

 

Question 11. Describe the structure of ethane (C₂H₆) with the help of a suitable diagram.

Answer:

The structure of ethane (C₂H₆) with the help of a suitable diagram

In ethane (C₂H₆), the two adjacent C-atoms equally share one electron pair among themselves to form a single bond. Each of the C- atoms then satisfies its remaining three valencies by forming three single bonds with three hydrogen atoms.

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Question 12. Describe the structure of ethylene (C₂H₄) with the help of a suitable diagram.

Answer:

The structure of ethylene (C₂H₄) with the help of a suitable diagram

In ethylene (C₂H₄), the two adjacent C-atoms share two electron pairs with each other to form a double bond and satisfy two of its valencies. Each of the two C-atoms then fulfils its remaining two valencies by forming single bond with two hydrogen atoms each. All the atoms in the molecule remain on the same plane.

 

 

Question 13. Describe the structure of acetylene (C₂H₂) with the help of a suitable diagram.

Answer:

The structure of acetylene (C₂H₂) with the help of a suitable diagram

In acetylene (C₂H₂), the two adjacent C-atoms share three electron pairs with each other to form a triple bond and satisfy three of its valencies. Each of the two C-atoms then fulfils its remaining valency by forming a single bond with one hydrogen atom each. All the atoms in the molecule remain in the same line and so, the molecule is linear in shape.

 

Question 14. What do you mean by functional group? Give one example.

Answer:

Functional group

An atom or a group of atoms present in an organic compound which determines the nature and characteristic chemical properties of the compound is called a functional group.

Example: —OH is the functional group of the alcohol series.

Question 15. Write the name and structure of the functional group of the alcohol series. Give an example of a compound containing that functional group.

Answer:

The name and structure of the functional group of the alcohol series.

The functional group of the alcohol series is the hydroxyl group and its structure is given by

2. A compound containing —OH as the functional group is ethyl alcohol (C₂H₅OH).

Question 16. Write the name and structure of the functional group present in aldehydes. Give an example of a compound containing that functional group.

Answer: The functional group present in aldehydes is the formyl or aldehydic group and its structure is given by:

 

 

A compound containing — CHO as the functional group is acetaldehyde (CH₃CHO).

Question 17. Write the name and structure of the functional group present in ketones. Give an example of a compound containing that functional group.

Answer: The functional group present in ketones is keto group and its structure is given by:

A compound containing     as the functional group is acetone (CH₃COCH₃)

Question 18. Write the name and structure of the functional group present in carboxylic acids. Give an example of a compound containing that functional group.

Answer: The functional group present in carboxylic acids is the carboxyl group and its structure is given by:

 

 

A compound containing — COOH as the functional group is acetic acid (CH₃COOH).

Types of Organic Reactions: Addition, Substitution, and Elimination

Question 19. Write the name and structure of the functional group present in amines. Give an example of a compound containing that functional group.

Answer: The functional group present in amines is the amino group and its structure is given by:

 

 

A compound containing -NH₂ as the functional group is methylamine (CH₃NH₂)

Question 20. Write the name and structure of the functional group present in ethers. Give an example of a compound containing that functional group.

Answer: The functional group present in ethers is the ether group and its structure is given by:

A compound containing — O — as the functional group is dimethyl ether (CH₃OCH₃).

Question 21. What is functional group isomerism? Give example.

Answer:

Functional group isomerism

The phenomenon of the existence of two or more compounds having the same molecular formula but different functional groups (i.e., belonging to different families) is called functional group isomerism.

Example: The functional groups in dimethyl ether (CH₃ — O — CH₃) and ethyl alcohol ( C₂H₅OH) are — O — and — OH respectively but both of these compounds have the same molecular formula of C₂H₆O.

Question 22. What is positional isomerism? Give example.

Answer:

Positional isomerism

The phenomenon of the existence of two or more compounds having the same structure of the carbon chain, i.e., the same carbon skeleton, but differing in the position of the multiple bond or functional group is called positional isomerism.

Example: The compounds, propan-1-ol or n- propyl alcohol (CH₃CH₂CH₂OH) and propan-2-ol or isopropyl alcohol [CH₃CH(OH)CH₃] both have the same molecular formula C₃H₈O, but the positions of — OH group is different in both the compounds.

Question 23. The members of a homologous series generally show similar chemical properties but different physical properties. Why?

Answer:

The members of a homologous series generally show similar chemical properties but different physical properties.

Due to the presence of the same functional group, the members of a particular homologous series show similar chemical properties. However, as the molecular masses of the members of a homologous series are different, the physical properties (such as melting point, boiling point, density etc.) dependent on the molecular mass of a compound are also different for the homologues.

Question 24. Only one alkyl group is formed from ethane whereas two different alkyl groups are formed from propane. Why?

Answer:

Only one alkyl group is formed from ethane whereas two different alkyl groups are formed from propane.

All the 6 H-atoms in an ethane molecule are equivalent. Hence, the removal of any one hydrogen atom from ethane produces the same alkyl group, i.e., the ethyl group ( — CH₂CH₃). On the other hand, two different types of hydrogen atoms are present in propane.

The two hydrogen atoms bonded to the central C-atom are different from the 6 H-atoms bonded to the terminal C-atoms in propane. So, the removal of the terminal H-atom produces an n-propyl group (CH₃CH₂CH₂—) whereas the removal of the non-terminal H-atom produces an isopropyl group

Question 25. Give the IUPAC names and structural formulas of the alkynes containing up to C-atoms.

Answer: HC = CH : ethyne
H₃C — C Ξ CH : propyne

Question 26. Give the IUPAC names and structural formulas of the alcohols containing up to 3 C-atoms.

Answer:

 

Question 27. Give the IUPAC names and structural formulas of the carbonyl compounds containing upto 3 C-atoms.

Answer:
Aldehydes:
HCHO: methanal
CH₃CHO : ethanal
CH₃CH₂CH₃CHO: propanal

Ketones:
CH₃COCH₃: propanone

Question 28. Give the IUPAC names and structural formulas of the carboxylic acids containing upto 3 C-atoms.

Answer:
HCOOH: methanoic acid
CH₃COOH: ethanoic acid
CH₃CH₂COOH : propanoic acid

Question 29. (1) Who proved that the main component of all organic compounds is carbon?
(2)All organic compounds contain carbon but all carbon compounds are not organic compounds. Explain

Answer:
(1) Scientist Lavoisier proved that the main component of all organic compounds is carbon.
(2) All carbon compounds are not organic compounds. Compounds like carbon monoxide, carbon dioxide, metallic carbonate, metallic bicarbonate, metallic cyanite etc. can not be termed as organic compounds as catenation property of carbon, isomerism etc. are not seen in these compounds. They all are inorganic compounds.

Question 30. What is a saturated compound? Give examples.

Answer:

Saturated compound

Organic compounds, in which all of the carbon atoms are attached through covalent single bonds are called saturated compounds.

Examples of saturated compounds are—

 

 

Question 31. What is an unsaturated compound? Give examples.

Answer:

Unsaturated compound

Organic compounds, in which at least two carbon atoms are attached through covalent double or triple bonds, are called unsaturated compounds.

Examples of unsaturated compounds are—

 

 

Question 32. What are alkenes or olefines? Give examples.

Answer:

Alkenes or olefines

Unsaturated hydrocarbons which contain at least one carbon-carbon double bond are called alkenes or olefins. The general formula of alkenes are C_nH_2n.

Examples: ethylene (CH₂=CH₂), propene (CH3 — CH = CH₂) etc.

Question 33. What are alkynes? Give examples.

Answer:

Alkynes

Unsaturated hydrocarbons which contain at least one carbon-carbon triple bond are called alkynes.

Examples: H — C Ξ C — H(acetylene),  CH3 — C=C-H(propyne)

Question 34. Differentiate between saturated and unsaturated hydrocarbons.

Answer:

Differences between saturated and unsaturated hydrocarbons are—

Topic	Saturated hydrocarbon	Unsaturated hydrocarbon
1. Nature of bond	Carbon atoms are attached through a covalent single bond.	At least two carbon atoms are attached through the double or triple bond.
2. Reactivity	Reactivity is comparatively less.	Chemical reactivity is comparatively more.
B. Nature of reaction	Usually participates in substitution reactions.	Usually participates in addition reactions.
4. Reaction with Br2 water	No reaction takes place. The red colour of bromine water remains unaltered.	An additional reaction takes place. The red colour of bromine water turns colourless.

 

Functional Groups in Organic Chemistry

Question 35. Why is C₂H₆ termed as saturated hydrocarbon but C₂H₄ is termed as unsaturated hydrocarbon?

Answer: All the carbon atoms of C₂H₆ are attached through the covalent single bond, hence it is termed as saturated hydrocarbon.

On the other hand, in C₂H₄, two adjacent carbon atoms are attached through a covalent double bond and hence it is termed as an unsaturated hydrocarbon.

Question 36. What do you mean by isomerism and isomer?

Answer:

Isomerism and isomer

1. The phenomenon of the existence of two or more compounds possessing the same molecular formula but different physical and chemical properties is known as isomerism.
2. Compounds with the same molecular formula but different physical and chemical properties, are termed as isomers to each other.

Question 37. Write down the definition and example of structural isomerism.

Answer:

Definition of structural isomerism

The phenomenon of existence of two or more compounds having the same molecular formula but different structures are called structural isomerism. For example, two structural isomers having the molecular formula C₂H₆O are—

H₃C — CH₂ — OH (ethanol) and H₃C — O —CH₃ (dimethyl ether)

Question 38. How would you identify two isomeric compounds denoted by the formula C₂H₆O? Or, Distinguish between ethanol and dimethyl ether by a chemical reaction.

Answer: Two compounds having same formula of C₂H₆O are dimethyl ether and ethanol. Ethanol reacts with sodium metal at room temperature, forming sodium ethoxide and H₂ gas. But dimethyl ether does not react with sodium.

2CH₃CH₂OH + 2Na → 2CH3CH₂ONa + H₂↑
CH₃ – O – CH₃ + Na → no reaction

Question 39. Write down the structural formula and IUPAC name of the following compounds:

1.CH₃CH₂CH₃
2. CH₂= CH₂
3.  H₃C-CH=CH₂
4. CH=CH
5.  CH₃-CH,CH
6. CH₃CH₂OH
7. CH₃CH(OH)CH₃
8. CH₃CH₂CH₂OH
9. CH₂(OH)CH(OH)CH₂(OH)
10. (CH₃)₃COH
11. C(CH₃)₃CHO
12. (CH₃)₂C= CH₂
13. CH₃COCH₃
14. CH₂(CI)CH₂(Cl)
15. CH₃CH(CI)CH₃

Answer:

Question 40. Write down the structural formula of—  

1. Ethanal
2. Methanoic acid
3. 2 -methyl propanal
4. 2,2-dichloro propane
5. Ethanoic acid
6. Ethanoic-1, 2-dioic acid
7. Tricloromethane
8. Methanol
9. Acetone

Answer:

 

Organic Chemistry Topic A General Properties Of Organic Compounds Answer In Brief

 

Question 1. Give the chemical equation for the reaction by which urea is produced from ammonium cyanate.
Answer: The chemical equation for the reaction by which urea is produced from ammonium cyanate is—

⇒ \(\underset{\text { (Ammonium cyanate) }}{\mathrm{NH}_4 \mathrm{CNO}} \frac{\text { heat }}{\text { (rearrangement) }} {\mathrm{NH}_2 \mathrm{CONH}_2}\)

Question 2. Give some examples of organic solvents.
Answer: Some examples of organic solvents are benzene, chloroform, acetone, ethanol etc.

Question 3. What are hydrocarbons?
Answer:

Hydrocarbons

The binary compounds of carbon and hydrogen are called hydrocarbons.

Question 4. What are saturated hydrocarbons?
Answer:

Saturated hydrocarbons

The hydrocarbons in which all the C-atoms are linked to one another through single covalent bonds only are called saturated hydrocarbons. For example, methane, ethane, and propane.

Question 5. What are unsaturated hydrocarbons?
Answer:

Unsaturated hydrocarbons

The hydrocarbons containing at least a double or a triple bond are called unsaturated hydrocarbons. For example, ethylene, and acetylene.

Question 6. Why are alkanes also known as paraffin?
Answer: Alkanes are also known as paraffin due to their less reactive nature.

Question 7. To which class do the organic compounds containing —the CHO group belong?
Answer: The organic compounds containing CHO as the functional group belongs to aldehyde.

Question 8. To which class do the organic compounds containing —CO— as the functional group belongs?
Answer: The organic compounds containing —CO — as the functional group belongs to the ketone.

Question 9. To which class do the organic compounds containing —COOH as the functional group belongs?
Answer: The organic compounds containing — COOH as the functional group belong to carboxylic acid.

Applications of Organic Chemistry in Daily Life

Question 10. To which class do the organic compounds containing —NH₂ as the functional group belongs?
Answer: The organic compounds containing —NH₂ as the functional group belongs to an amine.

Question 11. To which class do the organic compounds containing — O— as the functional group belongs?
Answer: The group name for organic compounds containing —O— as the functional group is ether.

Question 12. Name the first member of the alcohol homologous series. What is its IUPAC name?
Answer: The first member of the alcohol homologous series is methyl alcohol (CH₃OH).
Its IUPAC name is methanol.

Question 13. Name the first member of the aldehyde homologous series. What is its IUPAC name?
Answer: The first member of the aldehyde homologous series is formaldehyde (HCHO).
Its IUPAC name is methanal.

Question 14. Name the first member of the ketone homologous series. What is its IUPAC name?
Answer: The first member of the ketone homologous series is acetone (CH₃COCH₃).
Its IUPAC name is propanone.

Question 15. Name the first member of the carboxylic acid homologous series. What is its IUPAC name?
Answer: The first member of the carboxylic acid homologous series is formic acid (HCOOH).
Its IUPAC name is methanoic acid.

Question 16. Name the first member of the amine homologous series. What is its IUPAC name?
Answer: The first member of the amine homologous series is methylamine (CH₃NH₂).
Its IUPAC name is methenamine.

Question 17. Name the first member of the ether homologous series. What is its IUPAC name?
Answer: The first member of the ether homologous series is dimethyl ether(CH₃OCH₃).
Its IUPAC name is methoxymethane.

Question 18. What is isomerism?
Answer:

Isomerism

The phenomenon of the existence of two or more compounds having the same molecular formula but different chemical and physical properties is called isomerism.

Question 19. What do you mean by structural isomerism?
Answer:

Structural isomerism

The phenomenon of the existence of two or more compounds having the same molecular formula but different physical and chemical properties due to differences in their structures i.e., different bonding sequences is called structural isomerism.

Question 20. Between ethyl alcohol and dimethyl ether, which one does not react with metallic sodium?
Answer: Between ethyl alcohol and dimethyl ether, the latter does not react with metallic sodium.

Question 21. What is the minimum number of C-atoms required to represent the structural formula of a ketone?
Answer: A minimum of three C-atoms are required to represent the structural formula of a ketone.

Question 22. Name the two scientists who proved ‘the vital force theory’ wrong successfully synthesising acetic acid and methane in the laboratory.
Answer: Kolbe and Berthelot were the scientists who proved ‘the vital force theory’ to be wrong.

Question 23. Which two alkyl groups are formed when one hydrogen atom is removed from propane?
Answer: The two alkyl groups formed are—the propyl group (CH₃CH₂CH₂ —) and the isopropyl group (H₃C — CH — CH₃).

Word Problems on Organic Reactions with Solutions

Question 24. Why is ethanol called ‘grain alcohol’?
Answer: Ethanol is also called ‘grain alcohol’ because it can be prepared by the fermentation of finely ground grains (such as corn).

Question 25. Which type of chemical bond is present in organic compounds?
Answer: Covalent bond.

Question 26. Give an example of a biomolecule.
Answer: Glucose.

Question 27. State whether the organic compound of molecular formula C₄H₈ is saturated or unsaturated?
Answer: C₄H₈ (C_nH_2n, where n = 4) is an alkene compound, hence it is unsaturated in nature.

Question 28. Write down the number of H-atoms present in 4C-alkane.
Answer: The number of H-atoms in a 4C-alkane is 10.

Question 29. What is the number of H-atoms in a 3- carbon alkyne?
Answer: The number of ‘H’-atoms in a 3-carbon alkyne is 4.

Question 30. Name the simplest alkyne.
Answer: Ethyne (H — C = C — H).

Question 31. Which type of hydrocarbon is acetylene?
Answer: Acetylene is an unsaturated hydrocarbon.

Question 32. What is the H — C—H bond angle in methane molecules?
Answer: 109°28′

Question 33. How many chemical bonds are there in ethylene?
Answer: 6 chemical bonds are present in ethylene.

Question 34. Write down the H —C —H bond angle in ethylene.
Answer: The h — C—H bond angle in ethylene is 120°

Question 35. Give an example of a non-carbon functional group.
Answer: Hydroxyl ( — OH).

Question 36. Which type of isomerism can be seen in propanone and propanal?
Answer: Functional group isomerism.

Question 37. Write down the formula of functional group isomer of CH₃CH₂OH.
Answer: CH₃ — O — CH₃ (dimethyl ether)

Question 38. Write down the structural formula of positional isomer of CH₃CH₂CH₂OH.
Answer: Equation

Question 39. Write down the next two higher homologue of methane.
Answer: C₂H₆ (ethane) and C₃H₈  (propane).

Question 40. Write down the formula of first alkene homologue.
Answre: CH₂ = CH₂ (ethene)

Question 41. Write down the next homologue of C₂H₅OH.
Answer: The next homologue of C₂H₅OH is propanol (C₃H₇OH).

Question 42. Write down the full form of IUPAC.
Answer: International Union of Pure and Applied Chemistry.

Question 43. Write down the formula of prop-1-ene.
Answer: Formula of prop-1-ene is H₂C = CH — CH₃.

Question 44. Write down the IUPAC name of HC = CH.
Answer: IUPAC name of HC ≡ CH is ethyne.

Question 45. Write down the IUPAC name of CH₃CH₂OH.
Answer: ethanol.

Question 46. Write down the IUPAC name of CH₃CH₂CH₂OH.
Answer: propan-1-ol.

Question 47. Write down the IUPAC name of CH₃CH₂CHO.
Answer: propanal.

Question 48. Write down the IUPAC name of CH₃CH₂COOH.
Answer: propanoic acid.

 

Organic Chemistry Topic A General Properties Of Organic Compounds Fill In The Blanks

 

Question 1. Organic compounds are generally insoluble in ______ solvents.
Answer: Polar

Question 2. Most organic compounds are combustible due to the presence of _____ and _______.
Answer: Carbon, hydrogen

Question 3. Organic compounds do not ______ when dissolved in suitable solvents.
Answer: Ionise

Question 4. A carbon atom forms _______ bond with other atoms.
Answer: Covalent

Question 5. In most cases/carbon cannot form _____ compounds.
Answer: Ionic

Question 6. In the tetrahedral model of C-atom, all the four bonds of carbon atom does not remain on the ______ plane.
Answer: Same

Question 7. In the tetrahedral arrangement of four valencies of carbon, the carbon atom is present at the ______ of the tetrahedron and the four bonds are directed towards the four ______ of the tetrahedron.
Answer: Center, Corners

Question 8. The large number of organic compounds exists due to _____ and______ Of carbon.
Answer: Catenation, Isomerism

Question 9. The chain formed by carbon atoms due to catenation may be either ______ or ______
Answer: Open, Cyclic

Question 10. In methane, all the four valencies of carbon atom are satisfied by ______
Answer: Single, Bonds

Question 11. The ______ of an organic compound determines its chemical property.
Answer: Functional group

Question 12. The chemical reactivity of saturated hydrocarbons is very _____ while that of unsaturated hydrocarbons is quite ______
Answer: Less, high

Question 13. Between alcohols and ethers, _______ are relatively less reactive.
Answer: Ethers

Question 14. Between aldehydes and ketones, ______ are chemically more reactive.
Answer: Aldehyde

Question 15. If an alcohol and an ether are isomers, then it is an example of ______ isomerism.
Answer: Functional group

Question 16. Two adjacent members of a homologous series differ in their molecular formula by a _____ group.
Answer: CH₂

Question 17. All the compounds of a homologous series contain the same _____
Answer: Functional group

Question 18. The chemical properties of all the members of a homologous series is generally_________
Answer: Identical

Question 19. The phenomenon of similarity in the properties of the members of a homologous series is known as ________
Answer: Homology

Question 20. When one hydrogen atom is removed from ethane, _______ group is formed.
Answer: Ethyl

Question 21. The IUPAC name of the carboxylic acid having lowest molecular mass is _______
Answer: Methanoic acid

Question 22. The IUPAC name of the aldehyde containing two C-atoms is ______
Answer: Ethanal

Question 23. Covalent compounds are usually _________ in water.
Answer: Insoluble

Question 24.Different compounds with same molecular formula are ______ to each other.
Answer: Isomers

Question 25. n -propyl alcohol and isopropyl alcohol are _______ isomers.
Answer: Positional

 

Organic Chemistry Topic A General Properties Of Organic Compounds State Whether True Or False

 

Question 1. The first organic compound to be synthesised from an inorganic compound is acetic acid.
Answer: False

Question 2. Methane and ethane are saturated hydrocarbons while ethylene and acetylene are unsaturated hydrocarbons.
Answer: True

Question 3. In C₂H₂, the two adjacent carbon atoms are linked by a double bond.
Answer: False

Question 4. Alkenes are also called olefins because the lower members of this family react with halogens to form oily substances.
Answer: True

Question 5. Ethylene reacts with sulphur monochloride ( S₂CI₂) to produce mustard gas.
Answer: True

Question 6. C_nH_2n+1OH is the general formula of carboxylic acids.
Answer: False

Question 7. 2-bromopentane and 3-bromopentane are positional isomers.
Answer: True

Question 8. The molecular formula, C₃H₆O, represents two functional isomers namely, acetone and propionaldehyde.
Answer: True

Question 9. Thermal decomposition of organic compounds is known as pyrolysis.
Answer: True

Question 10. The first member of the aldehyde family is formaldehyde and its IUPAC name is ethanal.
Answer: False

Question 11. The IUPAC name of dimethyl ether is methoxymethane.
Answer: True

Question 12. Aldehydes and ketones are collectively known as carbonyl compounds.
Answer: True

Question 13. Ethane can decolourise the red colour of Br₂ dissolved in carbon tetrachloride solution.
Answer: True

Question 14. If one hydrogen atom is removed from propane, then two alkyl groups are formed namely, propyl and isopropyl.
Answer: True

Question 15. All the organic compounds are made of carbon.
Answer: True

Question 16. Catenation is the property of organic compounds.
Answer: False

Question 17. Formula of the 3-carbon alkane is C₃H₆.
Answer: False

Question 18. H —C —H bond angle in methane is 120°.
Answer: False

Question 19. C₂H₆ is a saturated hydrocarbon.
Answer: True

Question 20. Number of H-atoms in a 2-carbon alkane is 5.
Answer: False

Question 21. Functional group of alcohol is —OH .
Answer: True

Question 22. Common name of methanal is formaldehyde.
Answer: True

Question 23. IUPAC name of formic acid is methanoic acid.
Answer: True

Organic Chemistry Topic B Methane, Ethylene, Acetylene, LPG And CNG Synopsis

 

1. Methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂) are the first members of alkane, alkene and alkyne homologous series respectively. These compounds have extensive applications in different industries.
2. The gaseous component obtained at the time of refining crude petroleum by fractional distillation is liquefied under high pressure and stored in steel cylinders. This is known as LPG (Liquefied Petroleum Gas). It is widely used as a fuel.

3. The gas trapped in petroleum mines or coal mines is called natural gas. It is liquefied under high pressure and is known as CNG (Compressed Natural Gas). It is also used as a fuel. The main component of CNG is methane (~ 90%). Ethane, ethene, propane, butane and little amount of pentane is generally present in CNG, in addition to methane.

4. Methane is a saturated hydrocarbon belonging to the alkane family. It mainly participates in substitution reactions.

5. Combustion of methane: in presence of air, methane burns in a blue flame to form carbon dioxide and water.

⇒ \(\begin{array}{r}
\mathrm{CH}_4+2 \mathrm{O}_2 \rightarrow \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O}+\text { heat } \\
(213 \mathrm{kcal} / \mathrm{mol})
\end{array}\)

6. Ethylene is an unsaturated hydrocarbon belonging to the alkene family. It mainly participates in addition reactions. Polythene, a polymer of ethylene, has many practical applications.

7. Addition reaction of ethylene: When ethylene gas is passed through Br₂-solution (in CCI₄,CHCI₂), the red colour of the solution disappears and ethylene dibromide is formed.

8. Acetylene is an unsaturated hydrocarbon of the alkyne family and generally participates in addition reactions.

9. Uses of acetylene:
(1)Used to form oxyacetylene flame (3000°C)
(2)Used to form artificial rubber, artificial fibre, to lit carbide lamp, to form PVC etc.

9. Addition reaction of acetylene:
(1)Acetylene may be hydrogenated in presence of Ni- catalyst at 200°C, or in presence of Pt, Pd or Raney Ni catalyst at room temperature, to form ethylene and then ethane.

⇒ \(\begin{aligned}
& \mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H} \underset{2}{200^{\circ} \mathrm{C}} \mathrm{H}_2 / \mathrm{Ni}=\mathrm{CH}_2 \frac{\mathrm{H}_2 / \mathrm{Ni}}{200^{\circ} \mathrm{C} \downarrow} \\
& \mathrm{H}_3 \mathrm{C} \equiv \mathrm{CH}_3
\end{aligned}\)

(2)Acetylene decolourises the red colour of bromine-water as well as of liquid bromin.

⇒  \(\begin{array}{r}
\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}+\mathrm{Br}_2 \frac{\mathrm{H}_2 \mathrm{O}}{\longrightarrow} \mathrm{HCBr}=\mathrm{CHBr} \\
\text { (red). } \\
\begin{array}{c}
1,1,2,2 \text {-dibromoethene } \\
\text { (colourless) }
\end{array}
\end{array}\)

⇒  \(\begin{aligned}
& \mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}+2 \mathrm{Br}_2 \stackrel{\mathrm{H}_2 \mathrm{O}}{\longrightarrow} \mathrm{HCBr}_2-\mathrm{CHBr}_2 \\
& \text { (red) 1,1,2,2-tetrabromoethane } \\
& \text { (colourless) } \\
&
\end{aligned}\)

 

Organic Chemistry Topic B Methane, Ethylene, Acetylene, LPG and CNG Short And Long Answer Type Questions

Question 1. What are the important uses of methane?

Answer:

Important uses of methane

1. ‘Carbon black’ obtained due to cracking of methane is used in making black paint, printing ink and in rubber industries for making motor tyres.
2. Important chemical compounds such as methyl chloride, acetylene, formaldehyde, methanol are prepared from methane.
3. Due to high calorific value of methane (1000 Btu/ft³), it is used as a fuel.

Question 2. Mention some important uses of ethylene.

Answer:

Some important uses of ethylene

1. Ethylene is used in ripening and preservation of fruits.
2. It is used in the preparation of ethylene dichloride, ethylene dibromide, mustard gas (toxic in nature) etc.
3. It is used in the manufacture of plastics such as polythene, polystyrene etc., and synthetic fibres like nylon, terylene etc.
4. A mixture of 80% ethylene and 20% oxygen is used as an anesthetic in surgeries.

Question 3. Mention some important uses of acetylene.

Answer:

Some important uses of acetylene

1. Acetylene is used for producing oxy-acetylene flame, used for cutting steel and other metals.
2. It is used to produce bright illuminating flame in carbide lamps.
3. It is used in the industrial preparation of acetaldehyde, acetic acid, ethyl alcohol, acetone etc.
4. Acetylene is also used in the manufacture of industrial non-inflammable solvents like acetylene tetrachloride (westron, C₂H₂CI₄) and trichloroethylene (westrosol, CI₂C = CHCI) used in dissolution of fats, oil and resins.

 

 

Question 4. How will you distinguish between the following pairs of compounds? Ethylene and acetylene, ethane and acetylene, ethane and ethylene.

Answer:

Reagent	Ethylene	Acetylene
Ammoniacal Cu2CI2 solution	No precipitate is observed.	A red precipitate is formed.

 

Reagent	Ethane	Acetylene
Br2/CCI4 solution	No change in the colour of bromine solution.	The orange-brown colour or bromine solution disappears.

 

Reagent	Ethane	Ethylene
Br2/CCI4 solution	No change in the colour of bromine solution.	The orange-brown colour of bromine solution disappears.

Question 5. Write some important uses of LPG.

Answer:

Some important uses of LPG

1. As the calorific value of LPG is very high (29500 kcal/m³)it is used as a fuel for cooking purposes.
2. It is also used as a fuel in vehicles and industries.
3. As boiling point of LPG is quite low, it is also used as a refrigerant.

Question 6. What are the advantages of using LPG as a fuel?

Answer:

The advantages of using LPG as a fuel

1. As the calorific value of LPG is very high, it easily generates large amount of heat which is used up in heating other objects.
2. LPG undergoes complete combustion. So, it does not produce ashes or liberate poisonous gas such as CO during its combustion.
3. Using a regulator, the flow of LPG from the cylinder can be controlled. Hence, its combustion can be controlled depending upon the requirement of heat.
4. LPG cylinders can be conveniently transported to far off places as well.
5. It does not contain carbon monooxide and hence it is not harmful.

Question 7. Which sulphur compound is mixed with LPG? Why is this compound added?

Answer:
1. Ethyl mercaptan (C₂H₅SH) is mixed with LPG. It emits a very foul smell.
2. The gases constituting LPG are colourless and odourless but are highly imflammable. So, if these gases accidentally leak out of the cylinder, it is not possible to detect them which may lead to fatal accidents. So, as a precautionary measure, ethyl mercaptan is added to LPG as its characteristic foul smell help to detect any gas leakage thereby preventing accidents.

Question 8. Mention some important uses of CNG. Mention one environmental disadvantage of using CNG.

Answer:

Some important uses of CNG.

1. As the calorific value of CNG is very high (21300 Btu/lb), it is widely used as a fuel.
2. CNG causes least air pollution when it is used in vehicles. So, nowadays CNG is extensively used as a fuel in public transport like buses, autos, taxis etc.

Small amount of methane is released into the atmosphere due to the usage of CNG. Methane being a greenhouse gas causes global warming.

Question 9. What-are the advantages of using CNG as a fuel?

Answer:

The advantages of using CNG as a fuel

1. The carbon content of CNG is very low. So, it produces very less amount of carbon particles and CO₂ compared to other fuels during its combustion. Thus, CNG causes less air pollution.
2. It has a very high ignition temperature (1350°F). Hence, CNG does not burn easily which makes it safe to use.
3. No poisonous gas and ash are produced during combustion of CNG.
4. The calorific value of CNG (21300 Btu/ lb) is higher than that of diesel and LPG.

Question 10. What are the disadvantages of using CNG as a fuel?

Answer:

The disadvantages of using CNG as a fuel

1. As it is a gaseous fuel, the amount of heat generated by CNG per unit volume is low compared to other fuels.
2. The tanks required to store CNG are usually 3 to 5 times larger than those required for other fuels like diesel.
3. CNG being lighter than air- rises up and rapidly spreads in the atmosphere when it comes out of a cylinder. Consequently, the entire place gets covered by CNG leading to serious explosion.
4. During combustion of CNG, small amount of methane which is a greenhouse gas, is released into the atmosphere.

Question 11. Mention the industrial sources of methane ( CH₄).

Answer:

The industrial sources of methane ( CH₄)

1. The natural gas obtained from petroleum mines contains large amount of methane (40-90%).
2. Coal gas contains almost 40% (by volume) methane.
3. Methane is found in traces in the gas obtained from coal mines.
4. A mixture of CO₂ and H₂ or CO and H₂ when passed over hot Ni at 250-400°C, methane is produced.

⇒ \(\mathrm{CO}_2+4 \mathrm{H}_2 \underset{250-400^{\circ} \mathrm{C}}{\stackrel{\text { Ni-dust }}{\longrightarrow}} \mathrm{CH}_4+2 \mathrm{H}_2 \mathrm{O} \text {; }\)

⇒ \(\mathrm{CO}+3 \mathrm{H}_2 \underset{250-400^{\circ} \mathrm{C}}{\stackrel{\text { Ni-dust }}{\longrightarrow}} \mathrm{CH}_4+\mathrm{H}_2 \mathrm{O}\)

Question 12. Mention the major industrial sources of ethylene (C₂H₄).

Answer:

The major industrial sources of ethylene (C₂H₄)

1. The natural gas obtained from petroleum mines contains almost 20% of ethylene.
2. Ethylene is found in large volumes in coke oven gas.
3. Coal gas contains small amount of ethylene (almost 4%).
4. During cracking (the process by which long-chain hydrocarbons are degraded into smaller hydrocarbons by applying heat) of petroleum, ethylene is produced as a by product.

Question 13. Mention the major indu acetylene (C₂H₂).

Answer:

The major indu acetylene (C₂H₂)

1. Coal gas contains traces of acetylene (almost 0.06%)
2. Acetylene is produced by decomposing natural gas (mainly methane) at high temperature.

Question 14. What is LPG? Mention its industrial source?

Answer:

LPG:

1. LPG stands for Liquefied Petroleum Gas. It is a mixture of hydrocarbons of low molecular mass (upto 3-4 C-atoms). The major constituents of LPG are n-butane, propane, isobutane, butene etc. It also contains small amounts of propylene and ethane.
2. LPG is obtained by compressing the crude petroleum during refining into liquid under high pressure. It is stored in steel cylinders.

Question 15. Mention the constituents and industrial sources of CNG.

Answer:

The constituents and industrial sources of CNG

Constituents: The major constituent of CNG (Compressed Natural Gas) is methane (almost 90%). Apart from this, trace amounts of ethane, ethene, propane, butane and low-boiling pentane are also present in CNG.

Industrial sources: Natural gas is obtained above petroleum in petroleum mines and also from the coal mines. This gas is compressed into liquid by applying high pressure.

Question 16. Write with equation what happens when methane reacts with chlorine gas in presence of diffused sunlight.

Answer: In presence of diffused sunlight, methane undergoes substitution reaction with chlorine. In this case, the hydrogen atoms of methane are successively replaced by chlorine atoms one after another to form methyl chloride, methylene chloride, chloroform and carbon tetrachloride.

CH₄ + Cl₂ → CH₃CI (methyl chloride) + HCI
CH₃CI + Cl₂ → CH₂CI₂ (methylenechloride) + HCI
CH₂CI₂ + Cl₂ → CHCI₃ (chloroform) + HCI
CHCI₃ + Cl₂ → CCI₄ (carbon tetrachloride) + HCI

Question 17. Write down the hydrogenation reaction of ethylene specifying suitable conditions and chemical equation.

Answer: Hydrogen adds to the double bond of ethylene molecule at ordinary temperature and pressure in the presence of finely divided platinum or palladium or Raney nickel or at a temperature of about 200-300°C in the presence of finely divided nickel catalyst to produce ethane.

 

 

Question 18. What happens when ethylene gas is passed through bromine dissolved in carbon tetrachloride or in chloroform? Give equation. Or, How will you prove that ethylene is an unsaturated compound? Or, Give an example of addition reaction of ethylene.

Answer: When ethylene gas is passed through bromine dissolved in carbon tetrachloride ( CCI₄) or in chloroform (CHCI₃), the orange-brown colour of the solution is decolourised due to the formation of a colourless compound, ethylene dibromide or 1,2-dibromoethane. This reaction proves that ethylene is an unsaturated compound.

 

Question 19. Write a short note on polymerisation of ethylene.

Answer:

Polymerisation of ethylene

When ethylene is heated at 150 – 200°C in the presence of oxygen or peroxide catalyst under a very high pressure (1500-2000 atm), a large number of ethylene molecules combine with each other to form a solid compound of high molecular mass (approx. 20000) called polyethylene or polythene. This reaction is known as polymerisation of ethylene.

 

 

Question 20. Write down the hydrogenation reaction of acetylene specifying the suitable conditions and chemical equation.

Answer: Hydrogen reacts with acetylene at ordinary temperature in presence of Raney nickel or powdered platinum or palladium catalyst or at a temperature of about 200 – 300°C in presence of powdered nickel catalyst to produce ethane. The reaction occurs in two steps. In the first step, one molecule of hydrogen adds to acetylene to form ethylene and in the second step, another molecule of hydrogen adds to ethylene to form ethane.

Question 21. Which of the following hydrocarbons will participate in addition reactions— C₄H₁₀ ,C₃H₄ ,C₃H₆

Answer: Only unsaturated hydrocarbons participate in addition reactions. Among the given hydrocarbons, C₃H₆ (an alkene) and C₃H₄ (an alkyne) are unsaturated compounds and hence, undergo addition reactions. On the other hand,  C₄H₁₀ (an alkane) being a saturated compound does not undergo addition reaction.

Wbbse Class 10 Organic Compounds

Question 22. How will you prove that acetylene is an unsaturated compound? Or, What happens when an excess amount of acetylene gas is passed through bromine? Give equation.

Answer: When acetylene gas is passed through orange- brown coloured bromine water, 1,2- dibromoethene or acetylene dibromide is formed and consequently, the colour of bromine water is discharged. This reaction proves that acetylene is an unsaturated compound.

HC = CH + Br₂ → CHBr = CHBr
(orange-brown solution)  1,2-dibromo ethene (colourless)

Question 23. Three cylinders separately contain methane, ethylene and acetylene. How will you identify the gases?

Answer:

Three cylinders separately contain methane, ethylene and acetylene.

At first, the three gases are separately passed through ammoniacal cuprous chloride solution. The gas which produces a red precipitate is acetylene. After that, the two remaining gases are separately passed through bromine dissolved in CCI₄ solution. The gas which turns orange-brown solution of bromine colourless is ethylene. Thus, the remaining gas is definitely methene.

Question 24. what happens when methane is combusted in the presence of oxygen? Give balanced equations.

Answer: Methane burns with a light blue flame in excess air or oxygen and produces carbon dioxide, water vapour and huge heat is evolved.

⇒ \(\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H} \stackrel{\mathrm{CuCl}_2}{\longrightarrow} \mathrm{H}-\underset{\text { red ppt }}{\mathrm{C} \equiv \stackrel{\ominus}{\mathrm{C}} \mathrm{Cu}^{\oplus} \downarrow}\)

Question 25. What is Will-o’-the-wisp?

Answer:

Will-o’-the-wisp

Methane is formed in marshy lands due to the bacterial decomposition of organic matter. Moreover, phosphine (PH₃) and phosphorous tetrahydride (P₂H₄) are also formed as a result of the putrefaction of animal bodies. P₂H₄ rapdily burns in the air.

So when the mixture of CH₄, PH₃ and P₂H₄ comes in contact with air, P₂H₄ sets the gas mixture on fire and the heat produced causes methane to burn with a light blue flame. As a result, an intermittent source of light is produced. This is known as ‘Will-o’-the-wisp’.

Wbbse Class 10 Organic Compounds

Question 26. How will you prepare ethylene from acetylene?

Answer: In the presence of Lindler’s catalyst, acetylene combines with only one molecule of hydrogen to form ethylene.

⇒ \(\mathrm{HC} \equiv \mathrm{CH}+\mathrm{H}_2 \frac{\mathrm{Pd}-\mathrm{CaCO}_3 / \mathrm{Pb}(\mathrm{OAc})_2}{\text { Lindler’s catalyst }} \mathrm{H}_2 \mathrm{C}=\mathrm{CH}_2)\)

Question 27. A’ and ‘B’ are two unsaturated hydrocarbons with two carbon atoms in each. In reaction with bromine, each molecule of ‘A’ combines with 1 molecule of bromine and while each molecule of ‘B’ combines with 2 molecules of bromine. Write down the structure of ‘A’ and ‘S’. Write down the balanced equation for the reaction of ‘6’ with bromine.

Answer: Unsaturated hydrocarbons with two carbon atoms are ethylene and acetylene. Since each molecule of ‘A’ combines with 1 molecule of bromine, therefore ‘A’ is ethylene (CH₃ = CH₂). Again since each molecule of ‘6’ combines with 2 molecules of bromine, therefore ‘S’ is acetylene (HC ≡ CH).

Visual Representation of Organic Molecules

∴

 

Organic Chemistry Topic B Methane, Ethylene, Acetylene, LPG and CNG Answer In Brief

 

Question 1. What is carbon black?
Answer:

Carbon black

At 1000°C, methane decomposes to form fine particles of carbon which is known as carbon black.

⇒ \(\mathrm{CH}_4 \stackrel{1000^{\circ} \mathrm{C}}{\longrightarrow} \mathrm{C}+2 \mathrm{H}_2 \uparrow\)

Question 2. What are the uses of carbon black?
Answer: Carbon black is used in the manufacture of tyres, typewriter ribbons, printing ink, shoe polish etc.

Question 3. Which member of the alkane homologous series is the major constituent of natural gas?
Answer: Methane (CH₄) belonging to the alkane homologous series is the major constituent of natural gas.

Question 4. Give an example of a hydrocarbon which is also a greenhouse gas.
Answer: Methane (CH₄) is a hydrocarbon as well as a greenhouse gas.

Wbbse Class 10 Organic Compounds

Question 5. Which hydrocarbon is used in the industrial preparation of formaldehyde?
Answer: Methane (CH₄) is used in the industrial preparation of formaldehyde.

Question 6. Which hydrocarbon is used in the manufacture of industrial non-inflammable solvents namely Westron and Westrosol (used to dissolve fats, oils, resins etc.)?
Answer: Acetylene (C₂H₂) is used in the manufacture of industrial non-inflammable solvents namely Westron and Westrosol.

Question 7. Write with equation what happens when methane undergoes combustion in the presence of sufficient oxygen.
Answer: When methane undergoes combustion it burns with a pale bluish non-luminous flame in presence of sufficient oxygen or air to produce CO₂ and water vapour.

⇒ \(\begin{array}{r}
\mathrm{CH}_4+2 \mathrm{O}_2 \rightarrow \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O}+\text { heat } \\
\left(213 \mathrm{kcal} \cdot \mathrm{mol}^{-1}\right)
\end{array}\)

Question 8. Name the catalyst used in the addition reaction between ethylene and hydrogen.
Answer: Pt, Pd or Raney nickel is used as the catalyst in the addition reaction between ethylene and hydrogen.

Question 9. Under what conditions do the H-atoms of methane gets replaced by chlorine atoms in stepwise substitution reaction?
Answer: When chlorine reacts with methane in the presence of diffused sunlight the H-atoms of methane gets successively replaced by chlorine atoms in stepwise substitution reaction.

Question 10. What is the main component of marsh gas?
Answer: Main component of Marsh gas is methane (CH₄).

Question 11. Write down the formula of the organic compound formed in the first step of the substitutional reaction of methane with chlorine.
Answer: Formula of the compound is CH₃CI (methyl chloride).

Question 12. Which gas is responsible for Will- ‘O’-the wisp?
Answer: Methane gas (CH₄) along with phosphine (PH₃) and diphosphane (P₂H₄) are responsible for Will- ‘O’-the wisp.

Wbbse Class 10 Organic Compounds

Question 13. Which one undergoes addition reaction, saturated or unsaturated hydrocarbon?
Answer: Unsaturated hydrocarbon undergoes addition reaction.

Question 14. How will you identify wheather an organic compound is unsaturated or not?
Answer: If the red colour of bromine water decolourises in reaction with the sample organic compound, it can be said that the sample organic compound is unsaturated.

Question 15. CaC₂ + 2H₂O → A + Ca(OH)2; Identify ‘A’.
Answer: ‘A’ is acetylene, HC = CH.

Question 16. Write down the name of the compound formed when acetylene gas is passed through red coloured bromine water.
Answer: 1,2-dibro methene (CHBr = CHBr)

Question 17. What is the main component of LPG?
Answer: Butane (C₄H₁₀).

Question 18. Mention the use of LPG.
Answer: LPG is used as fuel in cooking and industrial purpose.

Question 19. Which bad-smelling component is mixed with LPG?
Answer: Ethyl mercaptan ( C₂H₅SH)

Question 20. What is the industrial source of CNG?
Answer: The source is usually shale rock far beneath the earth’s surface. Again the trapped gas in petroleum mines is CNG.

Question 21. Which one of petrol and CNG causes comparatively lower air pollution when used as fuel for vehicles?
Answer: CNG causes comparatively lower pollution.

Question 22. Mention the use of CNG.
Answer: CNG is used as fuel in bus, taxi, auto rickshaws etc.

Organic Chemistry Topic B Methane, Ethylene, Acetylene, LPG and CNG Fill In The Blanks

Physical Science Class 10 West Bengal Board

Question 1. The characteristic odour of LPG is due to the presence of _______
Answer: Ethyl mercaptan

Question 2. Methane gas is used as a fuel because of its high ______
Answer: Calorific value

Question 3. At high temperatures, natural gas is decomposed to produce _______
Answer: Acetylene

Question 4. _______ is formed when all the hydrogen atoms in methane are replaced by chlorine atoms.
Answer: Carbon tetrachloride

Question 5. The number of organic compounds formed in the reaction between methane and chlorine is _______
Answer: 4

Question 6. The temperature of the oxy-acetylene flame is ______°C.
Answer: 3000

Question 7. The major constituent of LPG is ______
Answer: Butane

Question 8. To reduce air pollution, _______ is used as an alternative fuel nowadays in buses, taxis, auto-rickshaws and other vehicles.
Answer: CNG

Question 9. In the presence of excess oxygen, methane burns with a non-luminous, pale _____ flame.
Answer: Blue

Question 10. In addition reaction with hydrogen, each molecule of ethylene combines with _____ molecule of hydrogen.
Answer: One

Wbbse Class 10 Organic Compounds

Question 11. At normal temperature, ethylene is a while polythene is a ______ while polythene is a ______
Answer: Gas, solid

Question 12. The component of Marsh gas which ignites in contact with air is ______
Answer: P₂H₄

Question 13. 3’H’ atoms of methane when substituted by 3’CI’ atoms, ______ is formed.
Answer: Chloroform

Question 14. Full form of LPG is ______
Answer: Liquefied Petroleum Gas

Question 15. Full form of CNG is ______
Answer: Compressed Natural Gas

 

Organic Chemistry Topic B Methane, Ethylene, Acetylene, LPG and CNG State Whether True Or False

Physical Science Class 10 West Bengal Board

Question 1. Methane usually participates in additional reactions.
Answer: False

Question 2. A mixture of methane and oxygen explodes when it comes in contact with fire.
Answer: True

Question 3. The decomposition of acetylene at a temperature of about 1000°C produces fine particles of carbon called carbon black.
Answer: False

Question 4. LPG stands for Liquid Petroleum Gas.
Answer: False

Wbbse Class 10 Organic Compounds

Question 5. Acetylene is used to produce illuminating flame in carbide lamps.
Answer: True

Question 6. 10% methane is present in coal gas (by volume).
Answer: False

Question 7. The smell of H₂S can be smelled in leakage of the LPG cylinder.
Answer: False

Question 8. CNG produces comparatively lower pollutants than LPG.
Answer: True

 

Organic Chemistry Topic C Polymer, Ethyl Alcohol, Acetic Acid And Denatured Spirit Synopsis

 

1. A chemical reaction in which a number of simple molecules react to form a larger molecule of high molecular mass is called a polymerisation reaction. The large molecule formed in the reaction is called polymer and the small molecules forming the repeating units in the polymer are called monomers. For example, polyethene, PVC, and Teflon.

2. Non-biodegradable synthetic polymers create different environmental hazards. As the manufacture of biodegradable polymers is still not cost-effective yet, use of natural polymers such as cotton, jute, wood, paper etc., should be encouraged.
3. Ethyl alcohol, acetic acid and denatured spirit have different commercial utilities.

Wbbse Class 10 Physical Properties Of Organic Compounds

4. Uses of acetic add:
(1)Acetic acid is used to prepare white lead, and acetone. 0 5-8% aqueous solution of acetic acid is used to preserve fish, meat etc.

5. Methylated spirit or denatured spirit: Poisonous methanol (10%), a small amount of pyridine, naphtha, copper sulphate. etc.

6. Some polymers and their monomers:

Polymer	Name and formula of the monomer	Uses of polymer
1. Polythene or polyethene (PE)	Ethene or Ethylene (CH2 = CH2)	1. Used to prepare carry bags,2. used to prepare water pipes, water tanks, bottles, buckets, mugs etc.
2. Polyvinyl chloride(PVC)	Vinyl Chloride	1. To prepare a false ceiling, 2. to make an insulator of wire, 3. used to prepare an inner side of the refrigerator.
3. Polytetrafluroethylene (PTFE)	Tetrafluoroethylene(F2C = CF2)	1. prepare non-stick utensils,2. used as insulators in electrical goods, 3. To prepare several apparatus in the chemical lab.

 

Are mixed with ethyl alcohol to make it poisonous and non-drinkable. This mixture is termed as methylated spirit or denatured spirit.

7. Uses of denatured spirit:

1. Used as a solvent of paint or varnish.
2. Used as the fuel of spirit lamp and stove.

Physical Science Class 10 West Bengal Board

Organic Chemistry Topic C Polymer, Ethyl Alcohol, Acetic Acid And Denatured Spirit Short And Long Answer Type Questions

 

Question 1. Which compound is formed due to the polymerisation of ethylene? How does it differ from ethylene in terms of its properties?

Answer: Due to polymerisation of ethylene, the polymer polythene or polyethene is formed.

The difference in properties of ethylene and polythene are as follows—

Ethylene	Polythene
1. Ethylene is a gas at ordinary temperature.	1. Polythene is solid at ordinary temperature.
2. The molar mass of ethylene is constant. Its value is 28.	2. Polythene is formed by the combination of numerous ethylene molecules. Thus, its molar mass is very high (approx. 20000).
3. Being a gas, the molar volume of ethylene at STP is very high (22.4 L).	3. Being a solid, the molar volume of polythene at STP is very low.

 

Question 2. What are biodegradable and non-biodegradable polymers? Give examples.

Answer:

Biodegradable polymers

1. The polymers which are degraded by the enzymatic action of environmental microorganisms (such as bacteria, fungi etc.) to form simple molecules (such as CO₂, H₂O etc.) are known as biodegradable polymers.’

Example: Polymers obtained from animals and plants such as carbohydrates (cellulose, starch), protein, nucleic acids etc.

Non-biodegradable polymers

2. The polymers which are not degraded by the enzymatic action of environmental microorganisms (such as bacteria, fungi etc.) to form simple molecules such as CO₂, H₂O etc., are known as non-biodegradable polymers.

Example: Synthetic polymers such as polyethene, PVC, polystyrene, Teflon etc.

Physical Science Class 10 West Bengal Board

Question 3. Biodegradable polymers do not cause environmental pollution—Explain with a suitable example.

Answer:

Biodegradable polymers do not cause environmental pollution

Biodegradable polymers are degraded into simpler compounds such as CO₂, H₂O etc., due to the enzymatic action of different microorganisms (bacteria, fungi etc.) present in the environment. These compounds are not hazardous to the environment and thus, biodegradable polymers do not cause environmental pollution.

For example, cotton, straw, paper and wood are biopolymers or polymers originating from plant sources. Cellulose present in these biopolymers is degraded by the enzymatic action of microorganisms into compounds which are not harmful to the environment.

Question 4. How do non-biodegradable polymers cause environmental pollution?

Answer:
1. Most synthetic polymers are non-biodegradable in nature and hence, they are not easily decomposed. These polymers accumulate in the soil and prevent the free flow of air and water in the soil. This makes the soil infertile and unsuitable for agriculture.

Deposition of these polymers in the soil leads to the formation of toxic chemical compounds due to weathering which in turn adversely affects the useful soil microorganisms. Accumulation of plastics also blocks the drains and sewage canals which makes the sewage system ineffective.

2. Combustion of synthetic polymers produces poisonous gases like CO, SO₂, NO₂ etc., and causes air pollution.
3. PVC polymers may sometimes contain free vinyl chloride monomer. When water pipes, water tanks etc., made of PVC get damaged due to friction, the monometer(vinyl chloride) may mix with water, Vinyl chloride is carcinogenic in nature.

 

 

Physical Science Class 10 West Bengal Board

Question 5. What measures should be adopted to prevent pollution caused by non-biodegradable polymers?

Answer:

1. Extensive use of synthetic polymers such as plastics, polythene, PVC etc., should be reduced.
2. Recently, it has been possible to prepare some synthetic biodegradable polymers such as Nylon- 2, Nylon-6, PHBV etc. However, the cost of production of these polymers is very high.
3. Natural polymers such as paper, cotton, jute etc., are biodegradable in nature. Thus, the use of jute and paper for packaging purposes should be encouraged. The government must also initiate awareness campaigns for people to encourage the use of natural polymers.
4. Remoulding of plastic wastes into other useful substances by recycling is another way to control pollution caused by non-biodegradable polymers.

Question 6. Discuss some important uses of ethyl alcohol.

Answer:

Some important uses of ethyl alcohol

1. Ethyl alcohol is used as a solvent for resins, soaps, varnishes, rayons, scents, pigments, synthetic rubbers, synthetic fibres, medicines, etc. % 2. It is used in the preparation of ether, ethyl esters, ethyl halides, chloroform, acetic acid, ethylene, methylated spirit etc.
3. Power alcohol which is used as an automobile fuel is prepared by mixing ethyl alcohol with petrol.
4. In cold countries, a mixture of water and ethanol is used as the anti-freezing agent in the radiators of motor vehicles.

Question 7. Mention some important uses of acetic acid.

Answer:

Some important uses of acetic acid

1. Glacial acetic acid (anhydrous) is used as a solvent for many organic compounds. 0 Acetic acid is used to prepare chemical compounds such as acetone, ethyl acetate, acetic anhydride, acetyl chloride etc.
2. Cellulose acetate, used for the preparation of photographic films and synthetic fibres (rayon), is prepared from acetic acid.
3. Vinegar (5-8% aqueous solution of acetic acid) is used as a preservative for fish, meat, etc., and also for making pickles and chutneys.

Question 8. What are polymers and monomers? Give example.

Answer:

Polymers and monomers

The giant molecules of high molecular mass formed by the polymerisation of a large number of small molecules, linked together in long chains of varying lengths are called polymers. The small molecules forming the repeating units in polymers are called monomers.

Physical Science Class 10 West Bengal Board

Example: A large number of ethylene molecules combine with each other to form polyethene. Hence, polyethene is the polymer while ethylene is its monomer.

Question 9. Write the name and structural formula of the monomer of polythene. Write some lines of polythene.

Answer: The monomer of polythene is ethene or ethylene and its structural formula is CH₂ = CH₂.

Uses of polythene: It is used as a packaging material and in the manufacture of carry bags, water pipes, water tanks, bottles, buckets, and window nets and as electrical insulation for being a non-conductor of electricity.

Question 10. Write the name and structural formula of the monomer of polyvinyl chloride (PVC). Write some uses of PVC.

Answer: The monomer of polyvinyl chloride (PVC) is vinyl chloride and its structural formula is CHCI.

Uses of PVC: It is used in the manufacture of electrical wires and cable insulation, water pipes, water tanks, raincoats, artificial flooring, handbags, tubings and hoses for corrosive materials etc.

 

 

 

 

Question 11. Write the name and structural formula of the monomer of polytetrafluoroethylene (PTFE) or Teflon. Write some uses of Teflon.

Wbbse Class 10 Physical Science Solutions

Answer: The monomer of Teflon is tetrafluoroethylene and its structural formula is F₂C — CF₂.

Uses Of Teflon: It is used in making non-stick cookware, as an insulating cover in electrical appliances, in making pipes and tanks for carrying corrosive substances and for making laboratory apparatus.

Question 12. Biodegradable polymers are more eco-friendly than non-biodegradable polymers. Explain.

Answer:

Biodegradable polymers are more eco-friendly than non-biodegradable polymers.

Uncontrolled use of non-biodegradable polymers is a major cause of environmental pollution. So, the use of natural polymers such as cotton, wood, paper, jute etc., should be encouraged until and unless the cost of manufacture of biodegradable polymers can be minimised. Jute and paper should be extensively used for packaging. Jute bags instead of plastic bags should be used for carrying things. As these are biodegradable polymers, they do not cause pollution.

Wbbse Class 10 Physical Science Solutions

Question 13. Write the equation of what happens when absolute ethanol is heated with excess concentrated  H₂SO₄ at 170°C. What wifi happens if the reaction is carried out with excess ethanol instead of excess acid?

Answer: When absolute ethanol is heated with excess concentrated  H₂SO₄ at 170°C, ethanol undergoes dehydration to produce ethene.

CH₃CH₂OH + H₂SO₄ (conc.) → CH₂ = CH₂ (ethene) + H₂O
(excess)

If the reaction is carried out in presence of excess ethanol instead of excess acid at a temperature of 140°C, then diethyl ether is produced instead of ethene.

CH₃CH₂OH + HOCH₂CH₃ → CH₃CH₂ —O—CH₃CH₂ + H₂O

Question 14. Write with an equation of what happens when sodium hydroxide reacts with acetic acid.

Answer: Acetic acid reacts with sodium hydroxide solution to form sodium acetate or sodium ethanoate (CH₃COONa) and water.

CH₃COOH + NaOH → CH₃COONa + H₂O

Question 15. Write with an equation what happens when sodium bicarbonate reacts with acetic acid.

Answer: Acetic acid (CH₃COOH) reacts with sodium bicarbonate (NaHCO₃) to form sodium acetate, water and carbon dioxide and the latter comes out of the reaction mixture as effervescence.

CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ ↑ + H₂O

Wbbse Class 10 Physical Science Solutions

Question 16. How will you distinguish between ethanol and acetic acid using sodium bicarbonate?

Answer: Ethanol does not react with sodium bicarbonate but, acetic acid reacts with sodium bicarbonate to form carbon dioxide which comes out of the solution as effervescence.

CH₃CH₂OH + NaHCO₃ → No reaction
CH₃COOH + NaHCO₃→ CH₃COONa + CO₂ ↑+ H₂O

Question 17. What is esterification? Describe the esterification reaction of ethyl alcohol and acetic acid along with a suitable equation.

Answer:

Esterification

1. In presence of a suitable catalyst such as concentrated H₂SO₄ or dry HCI, carboxylic acids react with dry alcohols to produce esters and water. This reaction is known as the esterification reaction.
2. When dry ethyl alcohol (CH₃CH₂OH) is heated with acetic acid (CH₃COOH) in presence of concentrated H₂SO₄ which acts as the catalyst, ethyl acetate (CH₃COOCH₂CH₃) having a fruity smell is formed.

 

 

Question 18. What are the physiological effects of consuming ethyl alcohol?

Answer:

Physiological effects of consuming ethyl alcohol

Consumption of limited amount of ethyl alcohol may act as a mild stimulant. However, if it is consumed in large quantities, it may lead to different physiological problems such as headache, nausea, reluctance to work, incoherence of speech, unconsciousness etc. Regular consumption of ethyl alcohol may lead to addiction which affects the liver and kidneys and may eventually lead to death.

Wbbse Class 10 Methanol Formula

Question 19. Briefly discuss the toxic effects of methanol.

Answer:

The toxic effects of methanol

Methanol is a highly toxic compound. Consumption of even a small amount of methanol may be fatal. It gets oxidised to form formaldehyde in the liver cells which rapidly reacts with certain components responsible for the formation of the cells. As a result, the protoplasm of the cell gets coagulated. Apart from this, methanol also damages the optic nerves which may cause blindness. Excess intake of methyl alcohol may even cause death.

Question 20. What is a methylated spirit or denatured spirit? Write its uses.

Answer:

Methylated spirit or denatured spirit

In order to prevent the use of ethanol as a beverage, it is made unfit for consumption by adding highly poisonous methyl alcohol (up to 10%) along with small amounts of certain compounds having a bitter taste such as pyridine, copper sulphate, naphtha etc. This mixture is known as methylated spirit or denatured spirit.

Uses: It is used as a solvent for paints and varnishes, as a fuel and in lighting stoves.

Wbbse Class 10 Methanol Formula

Question 21. Write down the differences between polymer and monomer.

Answer:

The differences between polymer and monomer are as follows—

Topic	Polymer	Monomer
1. Definition	Giant molecules formed by the chemical union of a large number of small molecules, Jinked together in long chains of varying lengths are called polymers.	The small molecules forming the repeating units in polymers are called monomers.
2. Molecular weight	The molecular weight of polymers is much higher than the corresponding monomers.	The molecular weight of monomers is less compared to that of polymers.
3. Formula	The formula varies with the number of repeating units and the process of polymerisation.	The formula of the monomer is fixed.
4. Example	Polytetrafluoroethylene (PTFE) or Teflon	The monomer of Teflon is tetrafluoroethylene (F2C = CF2)

 

Question 22. Which one between jute and polythene used in packaging is eco-friendly and why?

Answer: Jute is eco-friendly. Because jute is the natural polymer of carbohydrate molecule called cellulose. Being biodegradable, jute easily decomposes and mixes with soil, causing no harm to the environment. But polythene is a non- biodegradable polymer and hence does not mix with soil after use and causes environmental pollution in several ways.

Question 23. Identify A, B and C:

Answer:

 

Question 24. The molecular formula of an organic compound is   C₂H₄O₂. The compound is soluble in water and on the addition of NaHCO₃ in the aqueous solution of the compound, CO₂ gas evolved. Identify the compound. Write down the condition and balanced equation of the reaction of the organic compound with ethanol.

Answer:
1. Since the compound is organic, water-soluble and produces CO₂ in reaction with NaHCO₃, the compound must be a carboxylic acid i.e., the —  COOH group is present as a functional group.

Since the formula of the compound is C₂H₄O₂ so — CH₃ group must be added with — COOH.

The compound is CH₃COOH i.e., acetic acid.

Wbbse Class 10 Methanol Formula

2. In presence of heat and cone. H2S04, acetic acid reacts with ethyl alcohol producing sweet-smelling ethyl acetate ester and water.

 

Organic Chemistry Topic C Polymer, Ethyl Alcohol, Acetic Acid And Denatured Spirit Answer In Brief

 

Question 1. Which polymer is present in plant fibres such as cotton, jute etc.?
Answer: Plant fibres such as cotton, jute etc., are made of the polymer, cellulose.

Question 2. What is bio pool?
Answer:

Bio pool

The trade name for polyhydroxy butyrate (PHB) is bio pool. It is an eco-friendly and biodegradable synthetic polymer.

Question 3. Give an example of a biodegradable synthetic polymer.
Answer: Polyhydroxybutyrate is a biodegradable synthetic polymer.

Question 4. What are the uses of bio pool?
Answer: Biopol is widely used to make single-use products such as disposable cups, shaving razors, surgical threads etc.

Question 5. What is rectified spirit?
Answer:

Rectified spirit

A solution of 95.6% ethanol and 4.4% water is known as rectified spirit.

Question 6. Give an example of an organic compound which turns blue litmus red.
Answer: Acetic acid turns blue litmus red.

Question 7. Which organic compound is used to make pickles and chutneys?
Answer: Vinegar (5-8% aqueous solution of acetic acid) is used to make pickles and chutneys.

Wbbse Class 10 Physical Properties Of Organic Compounds

Question 8. What is vinegar?
Answer:

Vinegar

A 5-8% aqueous solution of acetic acid is commonly known as vinegar.

Wbbse Class 10 Methanol Formula

Question 9. How do biopolymers decompose in the natural environment?
Answer: Biopolymers decompose into simple molecules (like  CO₂, H₂O etc.) by the action of different microorganisms (fungi, bacteria etc.) present in the natural environment.

Question 10. Write down the name of the monomer of polythene.
Answer: The monomer of polythene is ethene or ethylene.

Question 11. What is PVC?
Answer:

PVC

PVC or polyvinyl chloride is the polymer of vinyl chloride (CH₂ = CH — Cl).

Question 12. Mention the use of polyvinyl chloride.
Answer: PVC is used to prepare corrugated roofing material.

Question 13. Name a polymer which is used to prepare raincoats, sandals or gumboots.
Answer: PVC or polyvinyl chloride.

Question 14. Write down the full form of PTFE.
Answer: Polytetrafluoroethylene.

Question 15. Mention the use of polytetrafluoroethylene.
Answer: Polytetrafluoro ethylene is used to prepare non-stick cooking utensils.

Question 16. Name two natural polymers.
Answer: Cellulose and protein.

Question 17. Which type of polymer is protein?
Answer: Protein is a biodegradable natural polymer.

Question 18. Name the monomer of the protein.
Answer: The monomer of protein is an amino acid.

Question 19. Mention an use of ethyl alcohol.
Answer: Ethyl alcohol is used to prepare rectified spirit (96.5% ethanol and 4.4% H₂O) which is used as an antiseptic.

Question 20. What is formed when ethyl alcohol is dehydrated by cone H₂SO₄?
Answer: Ethylene is formed when ethyl alcohol is dehydrated by the cone. H₂SO₄ .

Question 21. Write down the formula of a compound which can form ester in reaction with ethanol.
Answer: Acetic acid (CH₃COOH)

Question 22. Which gas is evolved when NaHCO₃ is added to acetic acid?
Answer: Carbon dioxide (CO₂)

Question 23. Which compounds are formed in the reaction of CH₃COOH with NaOH?
Answer: Sodium acetate (CH₃COONa) and water (H₂O).

Question 24. What is glacial acetic acid?
Answer:

Glacial acetic acid

Acetic acid that contains a very low amount of water (less than 1%) is called anhydrous acetic acid or glacial acetic acid. The reason it is called glacial is that it solidifies into white solid acetic acid crystals at 16.7°C.

 

Organic Chemistry Topic C Polymer, Ethyl Alcohol, Acetic Acid And Denatured Spirit  Fill In The Blanks

 

Question 1. Ethyl alcohol reacts with metallic sodium at ______ temperature to liberate _______ gas.
Answer: Ordinary, hydrogen

Question 2. The monomer of Teflon is _____
Answer: Tetrafluoroethylene

Question 3. ______ is mixed with petrol to produce power alcohol which is used as an automobile fuel.
Answer: Ethanol

Question 4. Ethyl alcohol on dehydration produces _____
Answer: Ethylene

Question 5. A mixture of 80% _____ and 20% ______ is used as an anaesthetic during surgeries.
Answer: Ethylene, oxygen

Question 6. Among all alcohols, _________ is toxic in nature.
Answer: Methanol

Question 7. Iodine dissolved in _______ is known as a tincture of iodine.
Answer: Ethyl alcohol

Question 8. The monomer of PVC is _______
Answer: Vinyl chloride

Question 9. ______ is used to prepare gramophone records.
Answer: PVC

Question 10. The polymer of phenol and formaldehyde is _______
Answer: Bakelite

Question 11. Ethyl alcohol reacts with metallic sodium at _______ temperature to form gas.
Answer: Normal, hydrogen

Question 12. _____ is mixed with petrol to form the fuel for a motor car called power alcohol.
Answer: Ethanol

Question 13. Almost ______ ethyl alcohol is present in rectified spirit.
Answer: 95.6%

Question 14. _______ can cause blindness by causing harm to the optic nerve.
Answer: Methanol

 

Organic Chemistry Topic C Polymer, Ethyl Alcohol, Acetic Acid And Denatured Spirit State Whether True Or False

 

Question 1. Oxygen or peroxide is used as the catalyst during the polymerisation of ethylene.
Answer: True

Question 2. The monomer of the polymer Teflon is vinyl chloride.
Answer: False

Question 3. Methanol on entering the body can damage the optic nerves.
Answer: True

Question 4. Polystyrene and polyethene are examples of non-biodegradable polymers.
Answer: True

Question 5. Petrol mixed with alcohol along with a cosolvent like benzene is called power alcohol.
Answer: True

Question 6. The basicity of acetic acid is 2.
Answer: False

Question 7. In spite of being an organic compound, ethyl alcohol is soluble in water due to its formation of hydrogen bonds with water molecules.
Answer: True

Question 8. The reaction between an alcohol and an aldehyde to form an ester in presence of concentrated sulphuric acid is called an esterification reaction.
Answer: False

Question 9. Teflon is used to prepare non-stick frying pans.
Answer: True

Question 10. Ethanol causes harm to the liver.
Answer: True

Question 11. Denatured spirit is used as a solvent of organic substances.
Answer: True

Question 12. Methylated spirit is poisonous due to the presence of methanol.
Answer: True

Miscellaneous Type Questions Match The Column

Question 1.

Column A	Column B
Dimethyl ether and ethyl alcohol	1. Chain isomers
n-propyl alcohol and propan-2-ol	2. Functional group isomers
n-pentane, isopentane and neopentane	3. Ring-chain isomers
Propene and cyclopropane	4. Positional isomers

 

Answer:
Dimethyl ether and ethyl alcohol: 2. Functional group isomers
n-propyl alcohol and propan-2-ol: 4. Positional isomers
n-pentane, isopentane and neopentane: 1. Chain isomers
Propene and cyclopropane: 3. Ring-chain isomers

Question 2.

Column A	Column B
Hydrogenation of ethylene	1. Undergoes substitution reactions
C4H10	2. Prepared acetic acid and methane from their constituent elements
Kolbe and Berthelot	3.  Alternative name for alkanes
Paraffin	4.  Ethane is formed as the product

 

Answer:
Hydrogenation of ethylene: 4.  Ethane is formed as the product
C₄H₁₀ :  1. Undergoes substitution reactions
Kolbe and Berthelot: 2. Prepared acetic acid and methane from their constituent elements
Paraffin: 3.  Alternative name for alkanes

Question 3.

Column A	Column B
Biopol	1. Natural polymer
Vinegar	2. Commercial name of tetrafluoroethylene
Teflon	3. Commercial name of polyhydroxybutyrate
Cellulose	4. 5-8% aqueous solution of acetic acid

 

Answer:
Biopol: 3. Commercial name of polyhydroxybutyrate
Vinegar: 4. 5-8% aqueous solution of acetic acid
Teflon: 2. Commercial name of tetrafluoroethylene
Cellulose: 1. Natural polymer

WBBSE Solutions for Class 10 Physical Science and Environment

Current Electricity Topic A Coulomb’s Law, Potential Difference, EMF Synopsis

WBBSE Class 10 Current Electricity Overview

1. Electric charge: Electric charge is the physical property of a matter due to which it exerts force on a charged body or on an uncharged body. There are two types of charges—positive charge and negative charge. Similar charges repel each other while opposite charges attract each other.

2. Coulomb’s law: The mutual attractive or repulsive force between two point charges at rest is directly proportional to the product of the charges and inversely proportional.to the square of the distance between them.

This law was given by the French scientist Charles Coulomb. If r is the distance between two point charges
q₁ and  q₂, from Coulomb’s law mutual force,

\(F=k \cdot \frac{q_1 q_2}{r^2}\)

Read and Learn Also WBBSE Solutions for Class 10 Physical Science and Environment

where k is the constant of proportionality. The value of k depends on the surrounding medium and the system of unit used.

3. Units of charge in CGS system and Sl are esu of charge and C (coulomb) respectively, 1C = 3 x 10⁹ esu of charge .
4. 1 esu charge: If two point charges of the same magnitude and of the same nature are placed in vacuum 1 cm apart and exert a repulsive force of 1 dyn on each other, then each charge is called a unit charge or 1 esu of charge or 1 statcouiomb in CGS system.
5. 1 coulomb charge: If two point charges of the same amount and of the same nature are placed in vacuum at a distance of 1 m and exert a repulsive force of 9 x 10⁹  N on each other, then each charge is called a unit charge or 1 C (coulomb) in SI.

6. Electric field: When a charge is kept at any place, it creates a field around it and if any other charge is kept there, it experiences an electric force. This area or field is called electric field.

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Understanding Electric Current and Its Measurement

7. Electric potential: Potential at a point in an electric field is defined as the amount of work done in bringing a unit positive charge from infinity to that point.

8. Units of electric potential in CGS system and in SI are respectively esu potential or statvolt and volt.

\(1 \text { volt }=\frac{1}{300} \text { statvolt }\)

9. 1 volt of potential difference: if 1 joule of work has to be done to move 1 coulomb of positive charge from one point to another point in an electric field, then the potential difference between these two points is called 1 volt of potential difference.

\(1 \text { volt }=\frac{1 \text { joule }}{1 \text { coulomb }}=1 \mathrm{~J} / \mathrm{C}\)

10. Electric cell: An electric cell is an arrangement in which other forms of energy like chemical energy, radiant energy can be converted into electric energy without the help of any appliance.

11. Electromotive force of a cell: The amount of work done by an external agency to move a unit positive electric charge from the positive pole of the cell to its negative pole is the electromotive force. V
12. If W work is done in taking a test charge q around the complete circuit of the cell, then emf of the cell is E = W/q.
13. SI unit of emf is volt (V).

Current Electricity Topic A Coulomb’s Law, Potential Difference, EMF Short And Long Answer Type Questions

Question 1. Write the mathematical form of Coulomb’s law.

Answer:

The mathematical form of Coulomb’s law:

Let two point charges q₁ and q₂ be placed at the points A and B respectively. The distance between these two charges is r. Now if F is the mutual force between the two charges, then according to Coulomb’s law, F ∝ q₁, q₂

\(F \propto \frac{1}{r^2}\) [when q₁, q₂ are constants]

Combining the above two conditions, we get \(F \propto \frac{q_1 q_2}{r^2}\) [when q₁, q₂, and r are variables]

or, \(F=k \cdot \frac{q_1 q_2}{r^2}\)

where k is a constant whose value depends on the surrounding medium and the system of units used.

Question 2. Give the definition of unit charge in CGS system with the help of Coulomb’s law.

Answer:

The definition of unit charge in CGS system with the help of Coulomb’s law:

Two point charges q₁ and q₂ are placed at a distance of r. Now if the mutual force between them is F, then according to Coulomb’s law

⇒ \(F=k \cdot \frac{q_1 q_2}{r^2}\) where k is a constant.

When the two charges are placed in vacuum, k = 1 in CGS system.

∴ \(F=\frac{q_1 q_2}{r^2}\) …….(1)

Here, q₁ = q₂ = q, r = 1 cm and F = 1 dyn.
So, we get from equation (1), q²  = 1 or, q = ± 1. Therefore, if two point charges of the same magnitude and of the same nature are placed in vacuum 1 cm apart and exert a repulsive force of 1 dyn on each other, then each charge is called a unit charge or 1 esu of charge or 1 statcoulomb in CGS system.

Wbbse Class 10 Physical Science Solutions

Question 3. Give the definition of unit charge in Si with the help of Coulomb’s law.

Answer:

The definition of unit charge in Si with the help of Coulomb’s law:

Two point charges q₁ and  q₂ are placed at a distance of r. Now if the mutual force between them is F, then according to coulomb’s law,

⇒ \(F=k \cdot \frac{q_1 q_2}{r^2}\), where k is a constant.

When the two charges are placed in vacuum, k =9x 10⁹ in SI.

∴ \(F=9 \times 10^9 \cdot \frac{q_1 q_2}{r^2}\) ……(1)

Here, q₁ = q₂ = q, r = 1 m and F = 9 X 10⁹ N

So from equation (1), we get 9 x 109 = 9 x 10⁹ • q²           or, q² = 1 or, q = ±1

Therefore, if two point charges of the same amount and of the same nature are placed in vacuum at a distance of 1 m and exert a repulsive force of 9 x 109 N on each other, then each charge is called a unit charge or 1 C (coulomb) in SI.

Question 4. Establish a relation between the units of charge in CGS system and SI.

Answer:

A relation between the units of charge in CGS system and SI:

The unit of charge in SI is C and the unit of charge in CGS system is esu of charge.

Suppose, 1 C = x esu of charge.

Now if two point charges of q₁ = q₂ = 1 C = x esu are kept at a distance of r = 1 m = 100 cm, then the mutual repulsive force is given by F= 9 x 10⁹ N = 9 x  10¹⁴ dyn .

Now according to the coulomb’s law,

⇒ \(F=\frac{q_1 q_2}{r^2}\)

or, x² = 9 x  10¹⁸ or, x = 3 x 10⁹

∴ 1 C = 3 x 10⁹ esu of charge

Question 5. Can we term Coulomb’s constant of the mutual force between two point charges as universal?

Answer:

The mathematical form of the Coulomb’s law regarding electrical force between two point charges q₁ and q₂ at a distance of r from each other in a medium is \(F=k \cdot \frac{q_1 q_2}{r^2}\) where k is called Coulomb’s constant.

The constant k depends on the nature of the medium. Therefore, mutual electrical force between two point charges depends on the nature of the medium and the value of this force is different in different media. Hence, Coulomb’s constant cannot be termed as universal.

Question 6. How can a charge Q be divded into two parts so that at a particular distance, mutual repulsisve force between them is maximum?

Answer:

Suppose the charge Q is divided into two portions q and (Q – q) and are kept at a distance of r from each other.

∴ mutual repulsive force, \(=k \cdot \frac{q(Q-q)}{r^2}\) [where, k is a constant]

or, \(F=\frac{k}{r^2}\left(Q q-q^2\right) \quad \text { or, } F=\frac{-k}{r^2}\left(q^2-Q q\right)\)

or, \(F=\frac{-k}{r^2}\left\{q^2-2 q \cdot \frac{Q}{2}+\left(\frac{Q}{2}\right)^2-\frac{Q^2}{4}\right\}\)

or, \(F=\frac{-k}{r^2}\left\{\left(q-\frac{Q}{2}\right)^2-\frac{Q^2}{4}\right\}=\frac{k}{r^2}\left\{\frac{Q^2}{4}-\left(q-\frac{Q}{2}\right)^2\right\}\)

For maximum value of F, q-Q/2 = 0 or, q = Q/2

∴ mutual repulsive force is maximum if the charge Q is divided into two equal parts, i.e., Q/2 and Q/2.

Question 7. Two bodies A and B have the same mass. A and B are charged respectively with equal amount of positive and negative charges. Find the change of their masses after charging.

Answer:

Given

Two bodies A and B have the same mass. A and B are charged respectively with equal amount of positive and negative charges.

Let us assume that charge of body A is q and that of body B is -q. Now if the charge of an electron is e, then q/e number of electrons are transferred from A and B. So when the mass of one electron is m, the mass of body A reduces by an amount qm/e and the mass of body B increases by an amount qm/e.

Question 8. Give the idea of potential difference in terms of work done to move one unit of positive charge Give the definition of the units of potential difference in CGS and Si from this.

Answer:

1. Potential difference between two points is the amount of work that has to be done to bring one unit positive charge from the point of lower potential to the point of higher potential.

Let,  V_R and V_s be the electric potentials of the two points R and S kept in an electric field. If V_S >  V_R, then the amount of work done to bring one unit of positive charge from point R to the point  S = V_S – V_R, which is the potential difference between the two points S and R.

2. The units of potential difference in CGS system and Si are esu of potential and volt (V) respectively.

1 esu of potential difference: If 1 erg of work has to be done to move 1 esu of positive charge from one point to another point in an electric field, then the potential difference between those two points is called 1 esu of potential difference.

1 volt of potential difference: If 1 joule of work has to be done to move 1 coulomb of positive charge from one point to another point in an electric field, then the potential difference between these two points is called 1 volt of potential difference.

Question 9. The potentials of two points S and R at a distance of r₁ and r₂ from a charge Q are V_S and V_R, respectively. If r₂>r₁, which point is at higher potential and which one is at lower potential? What is the potential difference between them?

Answer:

Given

The potentials of two points S and R at a distance of r₁ and r₂ from a charge Q are V_S and V_R, respectively. If r₂>r₁,

More the amount of work one to bring one unit positive charge from infinity to any point near another positive charge, more is its potential. For this reason, as r₂ > r₁,  V_S > V_R. Hence, point S will be at higher potential and point R will be at lower potential.

3. The potential difference between two points is the amount of work that is to be done to bring one unit positive charge from a lower potential point to a higher potential point. Therefore the potential difference between the two given points, V=V_S-V_R

Question 10. What is electric charge? How many types of charges are there? Name them.

Answer:

Electric charge:

1. Electric charge is that physical property of a matter due to which it exerts force on an electrified body or on an uncharged body.
2. It is of two types, namely positive charge and negative charge.

Question 11. When a material is electrically charged by rubbing, then what is the charge on the two materials?

Answer:

When a material is rubbed with another material, then some electrons get transferred from one material to the other. The material which has deficit of electrons is positively charged and the material which has excess of electrons is negatively charged.

Wbbse Class 10 Physical Science Solutions

Question 12. When does an electrically charged material attract another material? When does it repel another material?

Answer:
1. An electrically charged material attracts an uncharged material and also a material having a charge of opposite nature.
2. It repels a material having charge of similar nature.

Question 13. Write Coulomb’s law.

Answer:

Coulomb’s law:

The mutual attractive or repulsive force between two point charges at rest is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Question 14. When the distance between two point charges increases, how does the value of the mutual attractive or repulsive force between the change?

Answer: When the distance between two point charges increases, the value of the mutual attractive or repulsive force gets reduced in proportion to the square of the distance between the two.

Question 15. Define electric field.

Answer:

Electric field:

When a charge is kept at any place, it creates a field around it and if any other charge is placed in that area or field,it experiences an electric force. This area or field is known as an electric field.

Question 16. Define electric potential.

Answer:

Electric potential:

Electric potential at any point in an electric field is the total work done in moving a unit positive charge from infinity to that point under the influence of an external electric field.

In other words, we may say the total amount of work that has to be done in bringing one unit positive charge from infinity to a point near another positive charge is called the electric potential of that point with reference to the second charge.

Question 17. What are the units of electric potential in CGS system and SI? Define them.

Answer:

The units of electric potential in CGS system and SI:

The units of electric potential in CGS system and SI are esu of potential or statvolt and volt (V) respectively.

1. Esu of potential or statvolt: The potential at a point is said to be one esu of potential or one statvolt if 1 erg of work is done in bringing a positive charge of 1 esu from infinity to that point in an electric field.

2. Volt (V): The potential at a point is said to be one volt if 1 J (joule) of work is done in bringing a positive charge of 1 coulomb from infinity to that point in an electric field.

Wbbse Class 10 Physical Science Solutions

Question 18. Establish a relationship between esu of potential and volt (V).

Answer:

A relationship between esu of potential and volt (V)

When the potential difference at any point in an electric field is V, then the work done in bringing a charge of q from infinity to that point is given by

W = qV or, V = W/q

So, \(1 \mathrm{~V}=\frac{1 \mathrm{~J}}{1 \mathrm{C}}=\frac{10^7 \mathrm{erg}}{3 \times 10^9 \mathrm{esu} \text { of charge }}\) = 1/300 esu of potential

∴ 1 esu of potential = 300 V

Wbbse Class 10 Physical Science Solutions

Question 19. What is electromotive force? Or, In reality electromotive force (emf) is not any force—eKpiain the fact.

Answer:

Electromotive force:

1. The electromotive force of an electrical source is defined as the amount of electrical energy that is produced in the source due to the transfer of a positive charge from a lower potential to a higher potential.

2. In reality, electromotive force is not any force at all. It is the energy that is required to move per unit charge from lower potential to higher potential.

Question 20. Define the unit of emf in SI.

Answer:

Unit of emf in SI is J/C or V (volt).

1 volt of electromotive force: If 1J of work has to be done to move a positive charge of 1 coulomb from a point of low potential to a point of high potential in an electrical cell, then the magnitude of the electromotive force of that electrical cell is 1 J/C or 1 V.

Question 21. The emf of an electrical celt is 10 V’ — what do you, mean by this statement?

Answer: ‘The emf of an electrical cell is 10 V’ means that 10 J of work has to be done in order to move an electric charge of 1 C from a lower potential point to a higher potential point in the electrical cell.

Wbbse Class 10 Physical Science Solutions

Question 22. Define electromotive force for an open circuit.

Answer:

Electromotive force for an open circuit:

The electromotive force of a ceil for an open circuit is defined as the amount of work done by an external agency to move a unit positive electric charge from the positive pole of the cell to its negative pole.

Current Electricity Topic A Coulomb’s Law, Potential Difference, EMF Very Short Answer Type Questions Choose The Correct Answer

Question 1. Coulomb force is

1. Purely attractive force
2. Purely repulsive force
3. Either attractive or repulsive
4. Neither attractive nor repulsive

Answer: 3. Either attractive or repulsive

Question 2. Electric charges are of

1. A single type
2. Two types
3. Three types
4. Four types

Answer: 2. Two types

Question 3. The charge of an electron is

1. -3.2 × 10^-19 C
2. -1.6 × 10^-19 C
3. 1.6 × 10^-19 C
4. 3.2 × 10^-19 C

Answer:  3. 1.6 X 10^-19 C

Question 4. 450 V = how many statvolt?

1. 0.5
2. 1
3. 2
4. 1.5

Answer: 4. 1.5

Question 5. 0.1 C = how many esu of charge?

1. 3 × 10¹⁰
2. 3 × 10⁹
3. 3 x 10⁸
   
4. 3 x 10⁷

Answer:  4. 3 x 10⁷

Question 6. 1 J/ C is equal to

1. 1w
2. 1Ω
3. 1V
4. 1A

Answer: 3. 1V

Wbbse Class 10 Physical Science Solutions

Question 7. 2C charge is equivalent to the charge of how many electrons?

1. 6.25 × 10¹⁸
2. 6.25 × 10¹⁹
3. 1.25 × 10¹⁹
4. 12.5 × 10¹⁹

Answer: 3. 1.25 × 10¹⁹

Question 8. If the charge of an electron be 1.6 x 10^-19 C, which one of the following cannot be the charge of a body?

1. 1.6 x 10^-19 C
2. 0.8 x 10^-19 C
3. 3.2 x 10^-19 C
4. 4.8 x 10^-19 C

Answer: 2. 0.8 x 10^-19 C

Question 9. Unit of electromotive force is

1. Volt
2. Coulomb
3. Ohm
4. Ampere

Answer: 1. Volt

Question 10. Electromotive force is measured by

1. Ammeter
2. Voltmeter
3. Galvanometer
4. Potentiometer

Answer: 2. Voltmeter

Question 11. 1 V = how many esu of potential?

1. 3 x 10⁴
2. 1/3 x 10⁴
3. 1/300
4. 300

Answer: 3. 1/300

Current Electricity Topic A Coulomb’s Law, Potential Difference, EMF Answer In Brief

Question 1. What is the unit of electric charge?
Answer: The unit of electric charge in CGS system is esu of charge or stat coulomb.

Question 2. What is the unit of electric charge in SI?
Answer: The unit of electric charge in SI is coulomb (C).

Question 3. On which factors, does the value of the constant k of Coulomb’s law depend?
Answer: The value of the constant k depends on the nature of the surrounding medium and the system of unit.

Question 4. What is the value of k in CGS unit in the equation for Coulomb’s law, \(F=k \cdot \frac{q_1 q_2}{r^2}\) in vacuum?
Answer: The value of k is 1 in CGS unit in vacuum.

Question 5. What is the value of k in SI in the equation for Coulomb’s law, \(F=k \cdot \frac{q_1 q_2}{r^2}\) in vacuum?
Answer: The value of k is 9 x 10⁹ N • m² • C² in vacuum.

Question 6. What type of quantity is electric potential?
Answer: Electric potential is a scalar quantity.

Question 7. What is the relationship between electric charge (q) and work (l/V) with electric potential (V)?
Answer: Electric potential, V = W/q

Wbbse Class 10 Physical Science Solutions

Question 8. What is the unit of electric potential in CGS unit?
Answer: The unit of electric potential in CGS unit is esu of potential or statvolt.

Question 9. What is the unit of electric potential in SI?
Answer: The unit of electric potential in SI is volt (V).

Question 10. V • C is the unit of which physical quantity?
Answer: V-C is equal to J (joule) which is the unit of work and energy.

Question 11. What is the unit of electromotive force (emf) in SI?
Answer: The unit of electromotive force (emf) in SI is volt (V).

Question 12. Is Coulomb’s law a universal law?
Answer: No, Coulomb’s law is not a universal law.

Question 13. Does the mass of an uncharged body increase or decrease when it is charged with a positive charge?
Answer: When an uncharged body is charged with a positive charge, its mass decreases.

Question 14. Does the mass of an uncharged body increase or decrease when it is charged with a negative charge?
Answer: When an uncharged body is charged with a negative charge, its mass increases.

Question 15. What is the relationship between quantity of charge and amount of current flown through a conductor?
Answer: Amount of current flown through a conductor = \(\frac{\text { charge }}{\text { time }}\)

Question 16. Unit of which physical quantity is obtained when the unit of electric charge is divided by the unit of electric current?
Answer: Unit of time is obtained when the unit of electric charge is divided by the unit of electric current.

Question 17. Unit of which physical quantity is obtained when the unit of potential difference is multiplied by the unit of charge?
Answer: Unit of work is obtained when the unit of potential difference is multiplied by the unit of electric charge.

Question 18. What is the carrier of electricity in a metal conductor?
Answer: Free electron is the carrier of electricity in a metal conductor.

Current Electricity Topic A Coulomb’s Law, Potential Difference, EMF Fill In The Blanks

Question 1. A body is positively charged if there is ________ of electrons.
Answer: Deficit

Question 2. A body is negatively charged if there is ________ of electrons in it due to friction.
Answer: Excess

Question 3. The active mutual force between two point charges _____ on the nature of the medium.
Answer: Depends

Question 4. The potential at a particular point is _____ volt if 1/300 erg of work is done in bringing one esu of positive charge from infinity to that point in an electric field.
Answer: One

Question 5. Some other form of energy is transformed into _______ in an electric cell.
Answer: Electrical energy

Question 6. Force and electromotive force (emf) are ______ quantities.
Answer: Different

Question 7. Scientist _____ named two opposite type of charges as positive and negative.
Answer: Benjamin Franklin

Question 8. Electric charge is a _____ physical quantity.
Answer: Scalar

Question 9. In equation \(\mathrm{F}=k \cdot \frac{q_1 q_2}{r^2}\) SI unit of k is ______
Answer: n.m².C^-2

Current Electricity Topic A Coulomb’s Law, Potential Difference, EMF State Whether True Or False

Question 1. Charge of an electron is -1.6 x 10^-19C.
Answer: True

Question 2. Like charges attract each other and unlike charges repels each other.
Answer: False

Question 3. 1C = 3×10¹⁰ esu of charge.
Answer: False

Question 4. According to the Coulomb’s law, mutual force of attraction or repulsion is directly proportional to the square of the distance between the two given point charges.
Answer: False

Question 5. 1 V = 1/300 esu of potential.
Answer: True

Question 6. When a body is earthed, electrons from the earth flow into the body. This means that the body gets positively charged.
Answer: False

Question 7. According to Coulomb’s law if q₁ q₂ < 0, the force will be repulsive.
Answer: False

Question 8. In electric cell heat energy is converted into electric energy.
Answer: False

Current Electricity Topic A Coulomb’s Law, Potential Difference, EMF Numerical Examples Useful Relations

1. Charge of a body is q = ±ne, where e = charge of an electron and n is an integer.
2. Electrostatic force between two point charges and q2 kept in air or vacuum,

(1) \(F=\frac{q_1 q_2}{r^2}\) (in CGS system)

(2)F = 9 x 109 (in SI)

2. The amount of work done to bring a point charge q from a point of lower potential to a point of higher potential W = qV, V = potential difference between the two points.

1 V = 1/300 esu potential

Question 1. Two-point charges 25 esu and 12 esu are 5 cm apart in air. Calculate the force between the two charges.

Answer:

Given

Two-point charges 25 esu and 12 esu are 5 cm apart in air.

First charge (qx) = 25 esu

Second charge (q2) = 12 esu

Distance between the two charges (r) = 5cm

∴ mutual force between the two charges,

⇒ \(F=\frac{q_1 q_2}{r^2}=\frac{25 \times 12}{5^2}=12 \mathrm{dyn}\)

Question 2. There are two point charges in air at a distance of 2 m from each other. The magnitude of one charge is double than that of the other. If the force of repulsion between them is 7.2 x 10¹⁰ N, what is the value of each charge?

Answer:

Given

There are two point charges in air at a distance of 2 m from each other. The magnitude of one charge is double than that of the other. If the force of repulsion between them is 7.2 x 10¹⁰ N

Let us assume that first charge, q₁ = qC,

Second charge, q₂ = 2q C and the distance between the two charges, r = 2 m.

Mutual repulsive force, F= 7.2 x 10¹⁰ N

∴ from the equation, \(F=9 \times 10^9 \cdot \frac{q_1 q_2}{r^2}\), we get

⇒ \(7.2 \times 10^{10}=9 \times 10^9 \cdot \frac{q \times 2 q}{2^2}\)

or, \(q^2=\frac{4 \times 7.2 \times 10^{10}}{2 \times 9 \times 10^9}\)

or,  q² = 16 or, \(q=\pm 4\)

So, when \(q=\pm 4\), we get q₁ = 4C and q₂ = 2 x 4 = 8 C and when q = -4, we get q₁ = -4 C and q₂ = 2 × (-4) = -8 C

Question 3. Two point charges are kept at a distance of r and the mutual electrostatic force is F . What should be the distance between them for the value of force to become F/2?

Answer:

Given

Two point charges are kept at a distance of r and the mutual electrostatic force is F .

If the charges are q1 and q2, then \(F=k \cdot \frac{q_1 q_2}{r^2}\) ……(1)

where k is a constant.

Let us assume that the distance between the two charges is x so that the value of the mutual force, \(F_1=\frac{F}{2}\).

⇒ \(F_1=k \cdot \frac{q_1 q}{x^2}\) …..(2)

Dividing equation (1) by (2), we get

⇒ \(\frac{F}{F_1}=\frac{x^2}{\dot{r}^2}\)

or, \(2=\frac{x^2}{r^2}\left[because F_1=\frac{F}{2}\right]2=\frac{x^2}{r^2}\left[because F_1=\frac{F}{2}\right]\)

⇒ \(x^2=2 r^2 \quad therefore x=\sqrt{2} r\)

Question 4. A body M is rubbed with another body N and as a result, charge of M is 4.8 μC How many electrons have been exchanged during the process of rubbing?

Answer:

Given

A body M is rubbed with another body N and as a result, charge of M is 4.8 μC

Value of charge of one electron (e) = 1.6 x 10^-19 C

Charge of body M, q = 4.8 μC = 4.8 x 10^-6C

Let us assume that x number of electrons have been exchanged in this process.

or, \(x=\frac{q}{e} \quad \text { or, } x=\frac{4.8 \times 10^{-6}}{1.6 \times 10^{-19}}=3 \times 10^{13}\)

Hence, 3 x 10¹³ numbers of electrons have been transferred from body M to body N during the process of rubbing.

Question 5. Charge of body A becomes 6.4 x 10^-8 C when rubbed with another body B. What is the change of the mass of body A?

Answer:

Given

Charge of body A becomes 6.4 x 10^-8 C when rubbed with another body B.

Value of charge of one electron (e) = 1.6 x 10^-19 C

Charge of material A(q) = 6.4 x 10^-8C

If x number of electrons are transferred from A to B during the process of rubbing, then

⇒ \(x=\frac{q}{e}=\frac{6.4 \times 10^{-8}}{1.6 \times 10^{-19}}=4 \times 10^{11}\)

Again, the mass (m) = 9.1 x 10^-31kg

∴ Decrease of the mass of body A = mx= 9.1 x 10^-31 x 4 x 10¹¹ = 3.64 x 10^-19 kg

Current Electricity Topic B Ohm’s Law Synopsis

Ohm’s Law Explained with Examples

1. Electric current: The flow of electrically charged particles through any conductor is called electric current. The direction of electric current is given by the direction of motion of positive charges.

2. The amount of electrically charged particles flowing per second through any cross section of a conductor is known as the amount of electric current (l).

\(I=\frac{\text { total charge }(Q)}{\text { total time }(t)}\)

3. Unit of electric current in SI is ampere (A).
4. 1 A: A current of 1 A Is said to flow when a charge of 1C passes through any cross section of a conductor in 1 second.
5. The conventional direction of current is taken to be the direction of flow of positive charge i.e., opposite to the direction of flow of negative charge.
6. Current is a scalar quantity.

7. Ohm’s law: When temperature and other physical conditions of a conductor remain constant, the amount of current flowing through a conductor is directly proportional to the potential difference across the two ends of the conductor.

8. Mathematical expression: If the current flowing through a conductor is l when the potential difference across its two ends is V, then according to the Ohm’s law,
l ∝ V or, l = KV [where K is a proportional constant] or, V = 1/K • l or, V = R; [where 1/K = R(constant)] [where 1/K = R (constant)]
R is called resistance of the conductor.

9. The resistance of a conductor is defined as the property of the conductor due to which the flow of current through it is opposed.

10. Definition of resistance from Ohm’s law: When a potential difference is created across the two ends of a conductor, a current flows through the conductor. The ratio of the potential difference across the conductor to the amount of current flowing through the conductor is called the resistance of the conductor.

11. Unit of resistance in SI is ohm (Ω). \(\text { ohm }=\frac{\text { volt }}{\text { ampere }}\)

12. Those materials which easily conduct electricity are known as conductors.
Example: Any metallic conductor like iron, silver.

Those materials which cannot conduct electricity in general are known as insulators.
Example: Glass, plastic, rubber.

Those materials whose resistivity is more than that of a good conductor but less than that of an insulator are known as semiconductors.
Example: Germanium, Silicon.

13. There is a type of metal or substance whose resistivity becomes zero at a temperature less than a particular temperature. That particular temperature is called critical temperature and this type of substance is called superconductor.
Example: Mercury becomes a superconductor at 4.2K temperature.

14. When an electric current flows through an electric cell, then the constituents of the electric cell provides resistance to the current. This resistance inside the cell is known as the internal resistance.
15. Relation between emf and internal resistance of a cell: Let, an circuit is formed by connecting an electric cell of emf E, internal resistance r and an external resistance R , In closed circuit a current / is passing through the external circuit.

Now from Ohm’s law, we can write \(I=\frac{E}{R+r} \text { or, } E=I R+I r \text { or, } r=\frac{E-I R}{I}\)

15. Resistivity: The resistance of a conductor between the two opposite faces of a unit cube of the substance, when current passes normally through them is called resistivity.
16. If the length and area of cross section of a conductor at a particular temperature are l and A respectively, then its resistance,

\(R=\rho \frac{l}{A}\)

where ρ is resistivity of the material.

16. Unit of resistivity in SI is ohm • m (Ω • m)
17. Conductance: The property of a conductor due to which electricity can be conducted through it is called the conductance of the conductor.
18. If the resistance of a conductor is R, then its conductance, K= 1/R.

19. The unit of conductance is mho (℧). In SI, mho is called siemens (S).
20. The conductance of unit length of any conductor having unit cross sectional area is called the conductivity of the material of that conductor.
21. If the resistivity of the material of a conductor is ρ, its conductivity is \(\sigma=\frac{1}{\rho}\)

22. The unit of conductivity in SI is mho • m^-1(℧ • m^-1), but another unit S • m^-1 is also used.

23. Combination of Resistances: When a number of resistances are connected together in electrical circuit, then the combination is called combination of resistances.

24. Series combination: When several resistances are connected in such a way that the extreme end of one resistance is connected to the beginning of the next resistance and so on, then this combination is called a series combination.

So, if three resistances  R₁, R2 and R3 are connected in a series combination and if the equivalent resistance is Rs, then Rs = R1 + R2 + R3

25. Parallel combination: When several resistances are connected in such a way that the one of ends of all the resistances are connected to a particular point, while the other ends are also connected to another particular point, then this combination is called a parallel combination.

So, if three resistances R1, R₂ and R₃ are connected in a parallel combination and if the equivalent resistance is R_p, then \(\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}\)

Current Electricity Topic B Ohm’s Law Short And Long Answer Type Questions

Question 1. What are the directions of electric current and the flow of electrons in a metal conductor present in an electric circuit?

Answer:

The directions of electric current and the flow of electrons in a metal conductor present in an electric circuit are

In a metallic conductor, free electrons are the carriers of electricity. If a potential difference is applied across the two sides of a conductor, free electrons move from lower potential to higher potential. As a result, it is said that a current is passing through the conductor.

In a metallic conductor, the direction of electric current is opposite to the motion of the electrons. In other words, it has been assumed that the electrons flow from higher potential to lower potential.

Question 2. Write down Ohm’s law. Or, Explain the formula by which the relationship between the potential difference across the two ends of a conductor and the value of current through it can be known.

Answer:

Ohm’s law

According to Ohm’s law, if the temperature and other physical conditions remain constant, the amount of current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor.

Let us assume the potential across the two ends of a conductor are  V_A and V_B respectively. If V_A > V_B, then the current flows from A to B.

 

 

Now, if l is the current, then according to ohm’s law, l ∝ (V_A – V_B) or, \(\frac{V_A-V_B}{I}=k\)

or, V_A – V_B = kl, where k is a constant.

Question 3. What do you mean by the resistance of a conductor? Define resistance from Ohm’s law.

Answer:

Resistance of a conductor

1. Resistance is that property of a conductor due to which it obstructs the flow of current through it.
2. If a current l flows through a conductor when V is the potential difference across its two ends, then according to Ohm’s law, V ∝ l or, V/l = R (constant)

This constant is called the resistance of the conductor. In other words, the ratio between the potential difference across the conductor and the amount of current flowing through the conductor is called the resistance.

Question 4. What are ohmic conductor and non-ohmic conductor? Give examples.

Answer:

Ohmic conductor: Those conductors which follow Ohm’s law or those conductors for which l-V graph is a straight line passing through the origin, are called ohmic conductors.
Example: any metallic conductor

Non-ohmic conductor: Those conductors which do not follow Ohm’s law or those conductors for which l-V graph is not a straight line passing through the origin, are called non-ohmic conductors.
Example: electrolytic solution

Question 5. What are the factors on which the resistance of a conductor depends?

Answer:

Factors on which the resistance of a conductor depends are:

1. Length of the conductor,
2. Cross sectional area of the conductor,
3. Nature of the material of the conductor,
4. Temperature.

In addition, for some conductors, resistance depends on:

1. Intensity of light,
2. Strength of magnetic field,
3. Pressure.

Question 6. What are the factors on which the resistance of a conductor made of a particular material depends at a definite temperature? How?

Answer:

The factors on which the resistance of a conductor made of a particular material depends at a definite temperature

1. The resistance of a conductor (R) at a particular temperature depends on the length (l) and cross sectional area (A) of the conductor.
2. If the cross sectional area of the conductor remains unchanged, the resistance of the conductor is directly proportional to its length, i.e., R ∝ l [when A is constant].

Again, if the length of the conductor remains unchanged, the resistance of the conductor is inversely proportional to its cross sectional area, i.e., R ∝ 1/A [when l is constant].

Question 7. Define electrical conductance and electrical conductivity. Write down their expressions and their units in SI.

Answer:

Electrical conductance and electrical conductivity

1. The property of a conductor due to which electricity can be conducted through it is called the conductance of the conductor. If the resistance of a conductor is R, its conductance, K = 1/R.

The unit of conductance is mho (℧). In SI, mho is called siemens (S).

2. The conductance of unit length of any conductor having unit cross sectional area is called the conductivity of the material of that conductor. If the resistivity of the material of a conductor is p, its conductivity is σ = 1/ρ.

The unit of conductivity in SI is mho.m^-1(℧.m-1), but another unit S.m^-1is also used.

Question 8. Write down how the resistance of a metallic wire changes in the following cases:

1. Length -of the wire is doubled, diameter and temperature remain unchanged.
2. Diameter of cross section of the wire is doubled, length and temperature remain unchanged.
3. Keeping length and diameter unchanged, temperature of the wire is increased.

Answer:
1. The resistance of a wire is directly proportional to its length if the diameter and temperature of the conducting wire remain unchanged. Therefore, if length of the wire is doubled, its resistance will also be doubled.
2. If the length of the conducting wire and its temperature remain unchanged, then the resistance of the wire is inversely proportional to its cross section. Suppose, diameter was d initially. Therefore, cross sectional area,

\(A_1=\frac{\pi d^2}{4}\)

Now, if the diameter is doubled, cross sectional area becomes \(A_2=\frac{\pi(2 d)^2}{4}=\pi d^2=4 A_1\)

∴ cross-sectional area will be four times the previous one.

Therefore, present resistance of the wire is 1/4th of the previous resistance.

3. If the length of the conducting wire and its diameter remain unchanged, the resistance of the wire increases with increase of temperature.

Question 9. Two terminals of an electrical cell are connected by a wire. After that, the wire is folded into two and connected again with the same two terminals. In this condition, does the amount of current increase or decrease as compared to the first case?

Answer: As the wire is folded into two and is connected with the cell, the resistance of the folded wire will be half of the resistance of the original wire due to reduction of its length into half. Again, due to doubling of the area of cross section, resistance of the folded wire will be half of the original wire.

Therefore, due to change of length and cross section of the wire, the resistance of the folded wire will be (1/2 Χ 1/2) or 1/4th of its original resistance. Since the potential difference of the cell is constant, current through the folded wire is 4 times the current through the original wire as resistance and current are inversely proportional to each other.

Question 10. A thin and a thick Wire of the same length are connected with the same battery. In which wire is the value of current more and why? Explain.

Answer:
1. When a thin and a thick wire of the same length are connected with the same battery, value of current in the thick wire is more.
2. The resistance of a conductor is inversely proportional to the cross section, so the resistance of a thick wire will be less. Again, if the potential difference remains the same, value of current is inversely proportional to the resistance. Therefore, as a result of decrease of resistance of the thick wire, value of current in the conductor will be more.

Similarly, if the wire is thin, i.e., the cross section is reduced, the resistance of the wire will increase. Hence, as a result of increase of resistance, the value of current through the thin wire will be less.

Question 11. A copper wire is heated keeping its length and radius constant. Find the change in its resistance. If we take a carbon thread instead of a copper wire, will there be any change in the resistance?

Answer:

1. If a copper wire is heated by keeping its length and resistance constant, its resistance increases.

2. If a carbon thread is used instead of a copper wire and heated, the resistance of the thread will decrease. This is because the resistance of all pure metals and most metallic alloys increase with increase of temperature. But the resistance of carbon, electrolytes, rubber, silicon etc. decreases with increase of temperature.

Question 12. 1. How can you connect several resistance of lower value to get a resistance of higher value?
2. How can you connect several resistances of higher values to get a resistance of low value?

Answer:

1. When several resistances of lower values are connected in a series combination, a resistance of higher value can be obtained.

Example: Three wires of resistance 2Ω, 3Ω and 6Ω are connected in a series combination. The equivalent resistance of the combination R = (2 + 4 + 6) Ω =12 Ω

2. When several resistances of higher values are connected in a parallel combination, a resistance of lower value can be obtained.

Example: Three wires of resistances 2Ω, 3Ω and 6Ω are connected in-a parallel combination. The equivalent resistance is given by

⇒ \(\frac{1}{R}=\frac{1}{2}+\frac{1}{4}+\frac{1}{6}=\frac{11}{12}\)

∴ \(R=\frac{12}{11}=1.09 \Omega \text { (approx.) }\)

Types of Current: AC vs. DC

Question 13. Define conductor, insulator and semiconductor at electricity. What is the value of resistivity of each?

Answer:

Conductor: A conductor is a substance which easily conducts electricity.
Example: Any metallic substance.

Insulator: The value of resistivity of a good conductor lies between 10^-8 Ω • m and 10^-6 Ω • m(approx.). An insulator is a substance which in general, cannot conduct electricity.
Example: Glass, plastic, rubber etc.

Semiconductor: The value of resistivity of an insulator lies between 10¹⁰ Ω • m and  10¹⁷ Ω • m(approx.).

A semiconductor is a substance whose electrical conductance is less than that of a conductor but more than that of an insulator.
Example: Germanium, silicon.
The value of resistivity of a semiconductor lies between 10^-5 Ω • m and 10^-2 Ω • m (approx.).

Question 14. Write down the use of insulators in daily life.

Answer:

Use of insulators in daily life

If electric current passes through a conductor and if we touch it during that time, an electric shock can be felt. This is due to the fact that our body is a good conductor of electricity. Insulators protect us from this.

That is why an insulating material like coating of polyethylene is always applied on a conducting wire. For the same reason, a ceramic insulator is used in the overhead wire of trains. Also, handles of electrical instruments like pliers, tester etc. are made up of insulating materials.

 

 

 

 

Question 15. What do you mean by superconductivity? Draw a resistivity vs temperature graph to explain this.

Answer:

Superconductivity:

1. In general, if the temperature of a metal is reduced, its resistivity decreases. There is a type of metal or compound whose resistivity becomes zero if their temperature becomes less than a particular temperature. This particular temperature is called critical temperature. This type of phenomenon is called superconductivity and those materials are called superconductors.

2. In the given figure change of resistivity with temperature of this type of material is shown. In the graph, point C is the critical temperature.
For example, mercury at 4.2 K temperature, lead at 7 K temperature and Niobium Nitride (NbN) at 16 K temperature become superconductors.

 

 

Question 16. Explain series combination and parallel combination of resistance.

Answer:

Series combination and parallel combination of resistance:

Series combination: When some resistances are connected such that the extreme end of one is connected with the beginning of the next resistance and so on, then the resistance are said to be connected in series. When this combination is joined in an electrical circuit, the same current flows through each resistance after applying a potential difference across the combination.

Parallel combination: When some resistances are connected such that one of the ends of all the resistances is connected at a fixed point while the other end is connected to another point, then the resistances are said to be in parallel combination. When this combination is joined in an electrical circuit, potential difference across each of the resistance remains the same.

Question 17. Determine the equivalent resistance of three resistances connected in series combination.

Answer: The three resistances R₁,R₂,R₃ are connected in series at points A and D in the original circuit. Electric current (I) in the circuit is flowing in the direction from A to D which remains the same for each resistance.

Let us assume that the electric potential at the points A, B, C and D are V_A, V_B, V_C and V_D respectively.

 

∴ according to Ohm’s law,

V_A-V_B = IR₁ …(1)

V_B -V_C = IR₂ …(2)

V_C -V_D = IR₃ …(3)

Adding the above three equations, we get V_A-V_D = l(R₁ + R₂ + R₃) …(4)

Now, instead of these three resistances, a single resistance Rs is used in between the points A and D. If the same current l flows when the same potential difference is applied between A and D, then according to Ohm’s law, V_A-V_D = IR_S …(5)

By comparing the equations (4) and (5), we get Rs =R₁ + R₂ + R₃ ….(6)

So, R_S is the equivalent resistance of the series combination of three resistances.

Question 18. Write the characteristics of the series combination of resistances.

Answer:

The characteristics of the series combination of resistances are:

1. Same amount of electric current passes through each resistance.
2. Equivalent resistance of the combination is the algebraic sum of each individual resistance.
3. When a potential difference is applied between the two sides of the combination, potential difference between the two sides of each resistance is directly proportional to the respective resistance.
4. Equivalent resistance of the combination is more than the value of each resistance.

Question 19. Determine the equivalent resistance of three resistances connected in parallel combination.

Answer: The three resistances  R₁,R₂, R₃  are connected in parallel at points A and B in the original circuit.

The potential difference between the points A and B is V_A – V_B = V. Now, suppose the value of original current in the circuit is l and values of current through  R₁, R₂ and R₃ are I₁,  I₂ and  l₃ respectively. As the resistances are connected in parallel combination, the potential difference across the two sides of each resistance is the same.

 

 

Applying Ohm’s law, we get:

For the first resistance, V = I₁ R₁ ….(1)

For the second resistance, V = I₂ R₂ …..(2)

and for the third resistance, V = l₃R₃  ….(3)

Again, l =I₁+I₂ +l₃

or, \(I=\frac{V}{R_1}+\frac{V}{R_2}+\frac{V}{R_3}\)

or, \(I=V\left(\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}\right)\) ….(4)

Now, if a single resistance R_P is used in place of the three resistances in between the points A and B and if the same potential difference is applied to get the same value of current , then according to Ohm’s law,

⇒ \(V=I R_p \quad \text { or, } \quad I=\frac{V}{R_p}\) …..(5)

By comparing equations(4) and (5), we get

⇒ \(\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}\) …..(6)

or, \(R_p=\frac{R_1 R_2 R_3}{R_2 R_3+R_1 R_3+R_1 R_2}\)

So, R_P is called the equivalentr resistance of the three parallel resistance.

Question 20. Write the characteristics of the parallel combination of resistances.

Answer:

The characteristics of the parallel combination of resistance are:

1. The potential difference across the two terminals of each resistance is the same.
2. The reciprocal of the equivalent resistance of the combination is equal to the sum of the reciprocals of all the resistances.
3. The equivalent resistance of the combination is smaller than the smallest resistance of the combination.
4. As the terminal potential difference is constant, hence the value of current passing through a particular resistance is inversely proportional to that resistance.

Question 21. Calculate the equivalent resistance when n number of resistances, each of value R, are connected in series combination as well as in parallel combination. What is the ratio of thses two values?

Answer:
1. There are n number of resistances with values R₁, R₂, R₃  ••• R_n If they are connected in series combination, then the equivalent resistance
Rs = R₁+ R₂ + R₃ + …+ R_n 

Now, as R₁ = R₂ = R₃ = ••• = R_n  = R, so, R_S= nR Again, if the resistances are connected in parallel combination and their equivalent resistance is R_P, then

⇒ \(\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\cdots+\frac{1}{R_n}\)

As R₁ = R₂ = R₃ = • • • = R_n  = R, then \(\frac{1}{R_p}=\frac{n}{R} \text { or, } R_p=\frac{R}{n}\)

2. The ratio of equivalent resistances in the two cases, \(\frac{R_S}{R_p}=\frac{n R}{\frac{R}{n}}=n^2\)

Question 22. Show that the equivalent resistance of three resistances in parallel combination is smaller than the smallest resistance.

Answer: Let us assume that three resistances of values R₁, R₂ and R₃ are connected in parallel combination. R₁ is smallest among the three.
If R_P is the equivalent resistance of the combination, then

⇒ \(\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3} \quad \text { or, } \frac{1}{R_p}=\frac{1}{R_1}+x\)

[Here, \(\frac{1}{R_2}+\frac{1}{R_3}\) is taken as x, where x is a positive quantity.]

∴ \(\frac{1}{R_p}>\frac{1}{R_1} \quad \text { or, } R_p<R_1\)

∴ The equivalent resistance of three resistances.
In parallel combination is smaller than the smallest resistance.

Question 23. What are the constituents of a simple electrical circuit? What Is the direction of electric current in the entire circuit?

Answer:

Constituents of a simple electrical circuit

1. There are two parts of a simple electrical circuit-
(1) External circuit (entire portion except the cell) and
(2) Internal circuit (internal portion of the cell). At least one resistance must be present in the external circuit.

2. Once the key of the circuit is closed, an electric current starts flowing through the circuit and also through the resistance from the end of higher potential to the end of lower potential. In the internal circuit, this flow is from the negative terminal of the cell to the positive terminal.

Question 24. An electrical circuit has been formed by connecting a resistor, a voltmeter, an ammeter, an electric cell and a few pieces of
conducting wires.
1. Out of these, which electrical parts have, their own resistances and which parts have no resistance?
2. If we consider the parts to be ideal, then which ones will be without any resistance?

Answer:
1. According to the question, all the parts, namely, resistor, voltmeter, ammeter, electric cell, conducting wires possess some resistance. Out of these, the resistance of the conducting wire is considered to be negligible compared to the other parts.
2. If all the constituents had been ideal, then except the resistor and voltmeter, then all the other constituents namely ammeter, electric cell and conducting wires would have been without resistance.

Question 25. What is internal resistance of an electric cell? What Is the reason for the existence of this resistance?

Answer:
1. Resistance of the electric cell connected in an electrical circuit is the internal resistance of cell.
2. When an electric cell sends current through a closed circuit, then current flows also through the cell. The active liquid or electrolytic material placed between the two electrodes of this cell offers resistance to this current. This resistance inside the cell is the internal resistance.

Question 26. What is lost volt? What is the cause of its origin?

Answer:

Lost volt:

1. During the flow of electric current through the resistances of the external circuit and the internal circuit, some amount of work has to be done by each electric charge to overcome those resistances.

2. Therefore, some amount of electrical energy is converted to some other form of energy while passing through each resistance. The energy converted in the case of internal circuit is heat energy which cannot be used for any practical purpose. This wasted energy inside an electricai cell is known as lost volt.

3. The presence of the internal resistance of the electrical cell is the cause of origin of lost volt.

Question 27. Write down and explain the mathematical form of Ohm’s law for the entire circuit.

Answer:

According to Ohm’s law, electromotive force (E) for the entire circuit is given by: E=V+V’

where V = potential difference between the two terminals across the resistance R in the external circuit and V’ = amount of work that has to be done by an electric charge to overcome the resistance of the internal circuit, i.e., internal resistance (r) of the cell or lost volt.

Applications of Current Electricity in Daily Life

Question 28. The emf of an electrical cell and its internal resistance are E and r respectively. The cell is connected with an external resistance. What is the value of this external resistance If potential difference is half of the emf of the cell?

Answer:

Suppose the value of external resistance = R.
Current flow in the circuit, \(I=\frac{E}{R+r}\)

The potential difference across the two ends of the resistance (R)= \(R I=\frac{R E}{R+r}\)

According to the question,\(\frac{R E}{R+r}=\frac{E}{2}\) or, R + r = 2R or, r = R or, R = r

∴ The external resistance (R) has the same value as that of the internal resistance (r).

Question 29. Two resistances R₁ and R₂ are connected in parallel, if an electrical cell is connected with the combination, a current I flows through the circuit. Calculate the values of currents through R₁ and R₂.

Answer: Suppose the values of currents through  R₁ and R₂ are I₁ and I₂ respectively.

I = I₁+I₂ or, I₂ = I – I₁

 

 

Now as the two resistances  R₁ and R2 are connected in parallel, so the potential difference across the two ends is equal.

⇒ \(\begin{aligned}
& therefore \quad I_1 R_1=I_2 R_2 \\
& \text { or, } I_1 R_1=\left(I-I_1\right) R_2 \text { or, } I_1\left(R_1+R_2\right)=R_2 I \\
& therefore \quad I_1=\frac{R_2}{R_1+R_2} \cdot I \\
& \text { So, } I_2=I-I_1=I-\frac{R_2}{R_1+R_2} \cdot I \\
& \quad=\frac{R_1 I+R_2 I-R_2 I}{R_1+R_2}=\frac{R_1}{R_2+R_2} \cdot I
\end{aligned}\)

Alternative method: As the two resistances are connected in parallel, potential difference across the two ends of each resistance is equal. according to Ohm’s law, V = I₁R₁ = I₂R₂

Again, equivalent resistance, \(R=\frac{R_1 R_2}{R_1+R_2}\)

Let the main current = I

⇒ \(So, V=I R=I \frac{R_1 R_2}{R_1+R_2}\)

⇒ \(therefore \quad I_1 R_1=I \cdot \frac{R_1 R_2}{R_1+R_2} and I_2 R_2=I \cdot \frac{R_1 R_2}{R_1+R_2}\)

So, \( I_1=\frac{R_2}{R_1+R_2} \cdot I and I_2=\frac{R_1}{R_1+R_2} \cdot I\)

 

Question 30. If R = r in the circuit, calculate the value of l.

Answer: Let  R₁ is the resistance of the external circuit.

So, \(\frac{1}{R_1}=\frac{1}{R}+\frac{1}{R} \quad \text { or, } \frac{1}{R_1}=\frac{2}{R} \quad \text { or, } R_1=\frac{R}{2}=\frac{r}{2}\)

Now, current flow in the circuit, \(I=\frac{E}{R_1+r}=\frac{E}{\frac{r}{2}+r}=\frac{E}{\frac{3 r}{2}}=\frac{2 E}{3 r}\)

Question 31. Ordinary rubber is a bad conductor of electricity but the tyre of an aeroplane is made by a conductor of electricity to some extent. Why?

Answer: An aeroplane runs with high velocity at the time of take-off and landing. As a result, tyres are electrically charged due to friction of the runway and the tyres. There is a possibility of an accident due to this reason. As the tyres are made up of low conductors of electricity, charge produced by this friction goes to the earth and the possibility of an accident is averted.

Question 32. What is the function of an electrical source or electrical cell in an electrical circuit?

Answer: The function of an electrical cell is to create a permanent potential difference between the two ends of a conductor in an electrical circuit. The movement of charge takes place through the conductor as long as there is potential difference between the two ends, that is, the electrical cell is effective.

 

 

Question 33. What do you mean by short circuit?

Answer:

Short circuit:

1. If the two poles of any electrical source is connected by a conducting wire of negligible resistance, then that circuit is known as a short circuit.
2. As the resistance is low, flow of current becomes high causing the wire to get extremely heated. The electrical circuit may get damaged due to this.

Question 34. What is electric current?

Answer:

Electric current:

The flow of electrically charged particles through any conductor is called electric current. The magnitude of current is the amount of electrically charged particles flowing per second through any cross section of the conductor.

Question 35. What is the relationship between electric current and charge?

Answer: If q amount of charge passes through any cross section of a conductor in time t, then flow of charge per second = q/t.

∴ Electric current, I = q/t.

Question 36. Define the unit of electric current in SI.
Answer:

Unit of electric current in SI is A (ampere).

1 A: A current of 1 A is said to flow when a charge of 1 C passes through any cross section of a conductor in 1 second.

Question 37. Though electric current has a direction, why is it called a scalar quantity?

Answer: Electric current has both magnitude and direction but it is called a scalar quantity. This is because electric current does not follow the vector addition rule.

Question 38. Define the unit of resistance in SI.

Answer: The unit of resistance in SI is ohm (Ω) and it is given by \(1 \Omega=1 \frac{\mathrm{V}}{\mathrm{A}}\)

1Ω: If a current of 1 A flows through a conductor after the application of a potential difference of 1 V across its two ends, then the resistance of the conductor is called 1Ω.

Question 39. with the help of a graph, express Ohm’s law. Or, With the help of Ohm’s law, draw V-I graph.

Answer: According to Ohm’s law, V = IR.

Taking potential difference V as abscissa and current l through the conductor as ordinate, a graph is drawn. It will be a straight line passing through the origin.

 

 

Question 40. Define resistivity.

Answer:

Resistivity

The resistivity of a material is the resistance per unit length of a conductor having unit cross sectional area of the material at a definite temperature. In other words, it is defined as the resistance between the two opposite surfaces of a cube of unit length.

Question 41. What do you mean by the statement— ‘The resistivity of copper is 1.68 x 10^-6. cm (at 20°C temperature)’?

Answer:

‘The resistivity of copper is 1.68 x 10^-6. cm (at 20°C temperature)’

The statement, ‘The resistivity of copper is 1.68x 10^-6 Ω• cm (at 20°C temperature)’ means that the resistance between the two opposite surfaces of a cube of 1 cm side made of copper is 1.68 X 10^-6 Ωat 20°C.

Question 42. Determine the unit of resistivity In SI.

Answer:

Unit of resistivity In SI

If ρ is the resistivity of the material of a conductor of length l and cross sectional area A, then

\(R=\rho \cdot \frac{l}{A} \text { or, } \rho=\frac{R A}{l}\)

∴ The unit of resistivity in SI = \(=\frac{\text { unit of resistance in } \mathrm{SI} \times \text { unit of area in } \mathrm{SI}}{\text { unit of length is } \mathrm{SI}}\)

∴ \(=\frac{\Omega \times m^2}{m}=\Omega \cdot m\)

Question 43. How does pressure affect the resistance of a conductor?

Answer: In general, resistance of most of the metals decreases with the application of pressure. For example, resistance of carbon decreases with increase of pressure. But for Li, Ca and Bi, application of pressure increases the resistance instead of decreasing it.

Question 44. How does light affect the resistance of a conductor?

Answer: The resistances of some conductors depend on the intensity of incident light. The resistance of the metal selenium decreases when light is projected on it. With further increase of intensity, resistance keeps on decreasing.

Question 45. Current is passed through a wire With the help of an electrical cell. After sometime, it is observed that the wire gets heated and the amount of current decreases slightly. Explain this phenomenon.

Answer: When an electric current passes through a wire, it gets heated due to the production of heat in the wire. As the temperature of the wire increases, its resistance also increases. As a result, amount of current through it gets reduced. So, after sometime the amount of current flowing through the wire decreases.

Question 46. One silver wire and one iron wire of the same length and the same cross sectional area are taken. They are connected across the same electrical cell individually. The flow of electric current will be more in which case?

Answer: The resistance of a silver wire is less than that of a iron wire having the same length and the same cross section. Now if they are connected across the same electrical cell individually, then current through the silver wire will be more as its resistance is less.

Question 47. Draw- a graph which shows the change of resistivity of a semiconductor with the change of temperature.

Answer: The graph is shown below:

 

 

Question 48. There are two wires, one is thin and the other is thick. Both are made up of the same material and have the same length. Which wire will have more resistance and why?

Answer: The resistance of a conductor is inversely proportional to its cross sectional area when its length and material remain constant. Now as cross sectional area of a thin wire is less than that of a thick wire, so the resistance of a thin wire is more than that of a thick wire.

Question 49. What is equivalent resistance?

Answer:

Equivalent resistance

If a single resistance can be used in place of a combination of more than one resistance between the two points of an electrical circuit and when the same current flows through the circuit with the application of the same potential difference, then that single resistance is called an equivalent resistance of those resistances.

Question 50. How do you describe the emf in terms of work done inside a cell?

Answer: The magnitude of emf can be determined by the amount of work done to move a unit positive charge from the negative pole to the positive pole of a cell in an open circuit.

 

Current Electricity Topic B Ohm’s Law Very Short Answer Type Questions Choose The Correct Answer

 

Question 1. Which metal is the best conductor of electricity?

1. Gold
2. Silver
3. Aluminium
4. Copper

Answer: 2. Silver

Question 2. What is the equivalent resistance of a parallel combination of resistances 3Ω and 6Ω?

1. 2Ω
2. 4Ω
3. 9Ω
4. 3Ω

Answer: 1. 2Ω

Question 3. When the potential difference is 10 V and the amount of current is 5 A, then the resistance is

1. 5Ω
2. 4Ω
3. 3Ω
4. 2Ω

Answer: 4. 2Ω

Question 4. If R is the equivalent resistance of a parallel combination of three resistances R₁, R₂  and Rs (R₁> R₂  > R₃), then

1. R > R₁
2. R > R₂ 
3. R > R₃
4. R < R₃ < R₂  < R₁

Answer: 4. R < R₃ < R₂  < R₁

Question 5. The resistance of a superconductor at critical temperature is

1. Infinite
2. Zero
3. 10⁶ Ω
4. 10⁹ Ω

Answer: 2. Zero

Question 6. When temperature increases, the resistance of a semiconductor

1. Decreases
2. Increases
3. First increases then decreases
4. First decreases then increases

Answer: 1. Decreases

Question 7. What is the value of R at the time of a short circuit?

1. ∞
2. 0
3. 10⁶ Ω
4. 10¹⁰ Ω

Answer: 2. 0

Question 8. What is the value of R in an open circuit?

1. ∞
2. 0
3. 10 Ω
4. 1000 Ω

Answer: 1. ∞

Question 9. 1 A is equal to

1. 1 C²/s
2. 1 C/s²
3. 1 C/s
4. 1 s/C

Answer: 3. 1 C/s

Question 10. The carrier of electricity in a metal conductor is

1. Orbital electrons
2. Electrons and ions
3. Free electrons
4. Ions

Answer: 3. Free electrons

Question 11. When a charge of 120 C passes through a conductor for 2 minutes, what is the amount of electric current?

1. 1 A
2. 2 A
3. 0.5 A
4. 0.25 A

Answer: 2. 2 A

Question 12. 1 A = how many mA?

1. 10
2. 100
3. 1000
4. 10⁶

Answer: 3. 1000

Question 13. When  10¹⁹ electrons flow through any cross section of a conductor in 2 seconds, the amount of electric current

1. 0.8 A
2. 1.6 A
3. 2.4 A
4. 3.2 A

Answer: 1. 0.8 A

Question 14. 1 V/A is equal to

1. 1J
2. 1C
3. 1Ω
4. 1W

Answer: 3. 1Ω

Question 15. If temperature increases, resistance of a metal

1. Increases at first, then decreases
2. Decreases at first, then increases
3. Increases
4. Decreases

Answer: 3. Increases

Question 16. The unit of resistivity is

1. Ω-m²
2. Ω-m
3. Ω/m
4. Ω/m²

Answer: 2. Ω-m

Question 17. When the resistance of a conductor is 0.1 Ω, its conductance is

1. 0.1 S
2. 1 S
3. 10 S
4. 100 S

Answer: 3. 10 S

Question 18. When the resistivity of a conductor 2 x 10 8 n • m, then its conductivity is

1. 2 x 10⁷ S • m^-1
2. 2 x 10^-8 S • m^-1
3. 5 x 10⁷ S • m^-1
4. 5 x 10⁸ S • m^-1

Answer: 3. 5 x 10⁷ S • m^-1

Question 20. The value of resistivity is lowest in the case of

1. Metal
2. Insulator
3. Semiconductor
4. Superconductor

Answer: 4. Superconductor

Question 21. When n number of resistances, each of value R, are connected in series combination, its equivalent resistance is

1. (n + 1)R
2. (n – 1)R
3. nR
4. R/n

Answer: 3. nR

Question 22. When n number of resistances, each of value R are connected in parallel combination, its equivalent resistance is

1. (n + l)R
2. nR
3. R/(n+1)
4. R/n

Answer: 4. R/n

Question 23. What is the ratio of equivalent resistances of a combination of n number of resistances in series and in parallel, each of value R?

1. n²
2. n
3. 1/n
4. 1/n²

Answer: 1. n²

Question 24. In a series combination of several resistances, which of the following remains unchanged for each resistance?

1. Potential difference
2. Consumed power
3. Current
4. None of these

Answer: 3. Current

Question 25. In a parallel combination of several resistances, which of the following remains unchanged for each resistance?

1. Potential difference
2. Consumed power
3. Current
4. None of these

Answer: 1. Potential difference

Question 26. What is the equivalent resistance of two resistances R1 and R2 in Parallel combination?

1. \(\frac{R_1 R_2}{R_1-R_2}\)
2. \(\frac{R_1-R_2}{R_1 R_2}\)
3. \(\frac{R_1+R_2}{R_1 R_2}\)
4. \(\frac{R_1 R_2}{R_1+R_2}\)

Answer: 4. \(\frac{R_1 R_2}{R_1+R_2}\)

Question 27. Three identical resistances are connected in series. The equivalent resistance of the combination is 9 Ω. What is the value of each resistance?

1. 3 Ω
2. 4.5 Ω
3. 18 Ω
4. 27 Ω

Answer: 1. 3 Ω

Question 28. Four identical resistances are connected in parallel. The equivalent resistance of the combination is 2 Ω. What is the value of each resistance?

1. 4Ω
2. 16Ω
3. 8Ω
4. 32Ω

Answer: 3. 8Ω

Question 29. Two resistances are connected in parallel. If the potential difference is doubled, rate of heat production at a particular resistance becomes

1. Two times
2. Four times
3. Half
4. Eight times

Answer: 2. Four times

Question 30. Two resistances are connected in parallel. The ratio of these resistances is 1: 2. What is the ratio of the power consumed by the two resistances?

1. 1:2
2. 2:1
3. 4:1
4. 1:4

Answer: 2. 2:1

Question 31. Nichrome is

1. An alloy of Ni, Cr, Al
2. An alloy of Ni, Cr, Fe
3. An alloy of Al, Cr, Fe
4. An alloy of Ni, Cr, Fe

Answer: 2. An alloy of Ni, Cr, Fe

Question 32. Which physical quantity is compatible with electromotive force?

1. Force
2. Momentum
3. Acceleration
4. Power

Answer: 4. Power

Question 33. If the resistivity of a conductor with length l and cross sectional are a A is p, what is its conductance?

1. \(\rho \frac{l}{A}\)
2. \(\frac{\rho A}{l}\)
3. \(\frac{l}{\rho A}\)
4. \(\frac{A}{\rho l}\)

Answer: 4. \(\frac{A}{\rho l}\)

Question 34. If the resistance of a conductor with length l and cross sectional area A is R, its conductivity is

1. l/R
2. RA/l
3. l/RA
4. A/Rl

Answer: 3. l/RA

Question 35. The l-V curve of an ohmic conductor makes an angle θ with the positive side of the potential difference axis. What is the value of the resistance (R)?

1. R = sinθ
2. R = cosθ
3. R = tanθ
4. R = cotθ

Answer: 4. R = cotθ

Question 36. What is the equivalent resistance between A and B Shown In Fig?

1. 1Ω
2. 6Ω
3. 5Ω
4. 4Ω

Answer: 4. 4Ω

Question 37. What is the equivalent resistance between A and B shown in Fig. 16?

1. 2Ω
2. 3Ω
3. 1Ω
4. 4Ω

Answer: 1. 2Ω

Question 38. emf of the electric cell is 5 V and its internal resistance is 1Ω. What is the amount of current with a resistance of 4Ω?

1. 0.5 A
2. 0.75 A
3. 1 A
4. 1.25 A

Answer: 3. 1 A

Question 39. Amount of current is 0.5 A with a resistance of 9Ω. If the emf of the electric cell is 5V, what is the internal resistance?

1. 0.5A
2. 0.75Ω
3. 1Ω
4. 1.5Ω

Answer: 3. 1Ω

Question 40. Which of the following has the lowest resistivity?

1. Gold
2. Silver
3. Copper
4. Aluminium

Answer: 2. Silver

Question 41. A wire of resistance R is cut into two equal parts and these two parts are connected in parallel. What is the equivalent resistance?

1. R
2. R/2
3. R/8
4. R/4

Answer: 4. R/4

Current Electricity Topic B Ohm’s Law Answer In Brief

Question 1. What is the unit of resistance in SI?
Answer: Unit of resistance in SI is ohm (Ω).

Question 2. Give example of an ohmic conductor.
Answer: All metal conductors are ohmic conductors.

Question 3. Give examples of three non-ohmic devices.
Answer: Three non-ohmic devices are transistor, LED and filament lamp.

Question 4. What is the term used to describe the fall of potential inside an electric cell?
Answer: The fall of potential inside on electric cell is called lost volts.

Question 5. When an electric cell is connected with an external resistance, what is the direction of current flow in the external resistance?
Answer: The direction of current flow in the external resistance is from the positive pole towards the negative pole.

Question 6. When an electrical cell is connected with an external resistance, what is the direction of current flow inside the cell?
Answer: The direction of current flow inside the cell is from the negative pole towards the positive pole.

Question 7. What is the unit of resistivity in SI?
Answer: The unit of resistivity in SI is Ω• m.

Question 8. What is the unit of conductivity in SI?
Answer: The unit of conductivity in SI is S • m^-1.

Question 9. What is the unit of conductance in SI?
Answer: The unit of conductance in SI is siemens (S).

Question 10. When the resistance of the conductor is 100 Ω, what is the value of the conductance?
Answer: When the resistance of a conductor is 100 ft, the conductance of the conductor = 1/100 = 0.01 S 100.

Question 11. When the resistivity of a conductor is 4×10^-8 Ω • m, what is the value of its conductivity?
Answer: When the resistivity of a conductor is 4 x 10^-8 Ω • m, the value of its conductivity

= \(=\frac{1}{4 \times 10^{-8}}\) = 2.5 x 10⁷ S • m^-1

Question 12. What is the value of resistivity of a conductor at a temperature less than the critical temperature?
Answer: The value of resistivity of a conductor at a temperature less than the critical temperature is zero.

Question 13. How does the resistivity of a metal change if its temperature is increased?
Answer: The resistivity. of a metal increases if its temperature is increased.

Common Mistakes in Current Electricity Calculations

Question 14. How does the resistivity of a semiconductor change if its temperature is increased?
Answer: The resistivity of a semiconductor decreases if its temperature is increased.

Question 15. How would you connect some resistances, in series combination or in parallel combination, to get a resistance higher than the resistance of the individual constituents?
Answer: To get a resistance higher than the resistance of the individual constituents, the resistances have to be connected in a series combination.

Question 16. How would you connect some resistances, in series combination or in parallel combination, to get a resistance lower than the resistance of the individual constituents?
Answer: To get a resistance lower than the resistance of the individual constituents, the resistances have to be connected in a parallel combination.

Question 17. The household electrical instruments are connected in which combination?
The household electrical instruments are always connected in parallel combination.

Question 18. Which physical quantity, electric current or potential difference, remains constant for all the resistances connected in a series combination?
Answer: Electric current remains the same through each resistance connected in a series combination of resistances.

Question 19. Which physical quantity, electric current or potential difference, remains constant for all the resistances connected in a parallel combination?
Answer: Potential difference across the two ends of each resistance remains constant in a parallel combination of resistances.

Question 20. Two resistances R₁ and R₂(R₁> R₂) are connected in a parallel combination. Which resistance carries more current?
Answer: Between the two resistance R₁ and R₂, R₂ carries more current.

Question 21. Two resistances, each of value R, are connected in a parallel combination. What is the equivalent resistance?
Answer: If two resistances, each of value R, are connected in a parallel combination, its equivalent resistance becomes R/2.

Question 22. What are the values of two resistances such that the amount of current passing through them remains the same, when connected in series and in parallel combination?
Answer: The values of the two resistances should be equal.

Question 23. What is the value of the equivalent resistance, when three resistances 2Ω, 4Ω and 6Ω are connected in a series combination?
Answer: The equivalent resistance of the series combination = 2 + 4 + 6 = 12Ω.

Question 24. Which instrument is used to measure electric current?
Answer: Ammeter is used to measure electric current.

Question 25. Which instrument is used to measure potential difference?
Answer: Voltmeter is used to measure potential difference.

Queswtion 26. What is the condition for steady electric current through a conductor?
Answer: Steady electric current is obtained when the potential difference across the two ends of the conductor remains constant.

Question 27. How does the resistance of the metal selenium change when light rays fall on it?
Answer: When light rays fall on the metal selenium, its resistance decreases.

Question 28. How does the resistance of bismuth change when it is kept in a megnetic field?
Answer: When bismuth is kept in a magnetic field, its resistance increases.

Question 29. How does the resistance of carbon change when pressure on it is increased?
Answer: When pressure on carbon is increased, its resistance decreases.

Question 30. Write one use of superconductivity.
Answer: Superconductive magnet is a very powerful electromagnet. This type of magnet is used in a particle accelerator.

Current Electricity Topic B Ohm’s Law Fill In The Blanks

Question 1. Electric current is a _____ quantity.
Answer: Scalar

Question 2. .cm is the practical unit of ______
Answer: Resistivity

Question 3. The resistivity of a metal is _____ than that of a semiconductor.
Answer: Less

Question 4. If temperature increases, the resistance of germanium (Ge) ________
Answer: Decreases

Question 5. When a suitable impurity is doped inside a semiconductor, its resistivity ________
Answer: Decreases

Question 6. Electric current does not follow the law of _______ addition.
Answer: Vector

Question 7. When the potential difference across the two ends of a conductor is changed, the _______ passing through the conductor also changes.
Answer: Amount of current

Question 8. The nature of the l-V curve of a metallic conductor is a ______
Answer: Straight line

Question 9. If r is the internal resistance of a cell and l is the value of current, then rl is the _______
Answer: Lost volt

Question 10. The ______ of a conductor depends on its length, cross sectional area and its constituent material.
Answer: Resistance

Question 11. When temperature decrease, the resistivity of a metal also _______
Answer: Decreases

Question 12. The handle of an electrical instrument is made of an _______ material in order to avoid electric shock.
Answer: Insulating

Current Electricity Topic B Ohm’s Law State Whether True Or False

Question 1. The SI unit of electric potential is volt.
Answer: True

Question 2. Conductivity of a conductor is the reciprocal of the resistivity of the same conductor.
Answer: True

Question 3. Resistivity of a metal decreases as temperature increases.
Answer: False

Question 4. For a good conductor, resistivity is very low and conductivity is very high.
Answer: True

Question 5. If three resistances R₁,R₂ ,R₃  are connected in series, then the equivalent resistance R_S is given by \(R_S=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}\)
Answer: False

Question 6. In series combination of resistances, voltage remains the same through each resistance.
Answer: False

Question 7. In parallel combination of resistances, current remains the same through each resistance.
Answer: False

Question 8. If three resistances R₁,R₂ ,R₃  are connected in parallel, then the equivalent resistance R_P is given by \(R_p=\frac{R_1 R_2 R_3}{R_1 R_3+R_1 R_3+R_1 R_2}\)
Answer: True

Question 9. Out of a thin and a thick wire, both made up of same material and having same length, the thin wire has more resistance.
Answer: True

Current Electricity Topic B Ohm’s Law Numerical Examples

1. Electric current intensity I = q/t, where q = amount of charge flows through any cross section of the conductor in the time t
2. q = It
3. Mathematical expression of Ohm’s law is V=IR, where V – potential difference between two ends of the conductor I = electric current passing through the conductor, R = resistance of the conductor.

4. \(R=\rho \frac{l}{A}\), where l = length of the conductor, A = area of cross section of the conductor, ρ = specific resistance

5. Formula for the determination of equivalent resistance in series combination,  R_S = R₁ + R₂ + R₃ + …… + R_{n ,} if R1 = R2 = … = R_n= R then  R_S = nR.
6. Formula for the determination of equivalent resistance in parallel combination, \(\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2}+\cdots+\frac{1}{R_n}\)

For two resistances R₁ and ,R₂ \(\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2}=\frac{R_1+R_2}{R_1 R_2}\) or \(R_p=\frac{R_1 R_2}{R_1+R_2}\)

7. E = Ir+V, where E = emf of a cell, r = internal resistance of the cell and V = potential difference

8. Current through external circuit, \(I=\frac{E}{R+r}\)

9. Lost volt = Ir
10. Terminal potential difference of the cell, V = E – lr

Question 1. An electric current of 2 A is passing through a conductor. How much charge will flow in 5 seconds? When the carrier of charge in the conductor are free electrons, how many electrons flow through any cross section of the conductor?

Answer:
Electric current (l) = 2 A
Time (t) = 5 s
If q amount of charge flows, then l = q/t or, q= lt = 2×5 = 10C
Value of the charge of (e) = 1.6 x10^-19. C

Number of electrons flowing, through any cross section of the conductor \(=\frac{q}{e}=\frac{10}{1.6 \times 10^{-19}}=6.25 \times 10^{19}\).

Question 2. A current of 0.1 A flows when a potential difference of 10 V is applied across the two ends of a conductor. What is the resistance of the conductor?

Answer: Potential difference across the two ends of the conductor (V) = 10 V
Amount of current flowing (I) = 0.1 A
Now, if the resistance of the conductor = R, then according to Ohm’s law, V= IR or, \(R=\frac{V}{l}=\frac{10 \mathrm{~V}}{0.1 \mathrm{~A}}=100 \Omega\).

Question 3. There are two Conductors, the resistance of the first being three times that of the second. The amount of current flowing through the first is twice that of the second. What is the ratio of the potential difference of the two conductors?

Answer: Let us assume that the resistance and the amount of current passing through the second conductor are R and l respectively.
resistance of the first conductor =3R and current passing through the first conductor = 2I. Potential difference across the two ends of the first conductor,
V₁ = 3Rx2I =6RI….(1)
and potential difference across the two ends of the second conductor, V₂ = RI
Now dividing equation (1) by (2), we get \(\)or, V₁ : V₂ = 6 :1

Question 4. An electrical cell with internal resistance of 5 Ω and emf of 2 V is attached to a resistance of 15Ω. What is the potential difference across the two terminals of the cell?

Answer: Emf (E) of the electrical cell = 2 V
Internal resistance (r) = 5 Ω
Resistance of the external circuit (R) = 15 Ω
Let current in the circuit = I

 

So, \(I=\frac{E}{R+r}=\frac{2}{15+5}\)

∴ I + 0.1A

Hence, potential difference across the two terminals, V=IR = 0.1×15 = 1.5 V

Question 5. An electrical cell has an emf of 5 V. How much work has to be done in an open circuit by an external agency in moving a charge of 1C from cathode to anode inside the cell?

Answer: Emf (E) of the electrical cell = 5 V.
In an open circuit, charge inside the cell, q = 1C Now, work done by an external agency for moving the charge from cathod to anode is given by
W = qE= 1CX5V = 5J

Question 6. The emf and the internal resistance of an electrical cell are 10 V and 1 Ω respectively. The cell is connected to a resistance R = 9 Ω. How much work has to be done by the cell to move a positive charge of 1 C through the resistance R and also through the cell?

Answer: Emf of the cell (E) = 10V and internal resistance (r) = 1 Ω
Resistance in the external circuit (R) = 9 Ω

∴ Current in the circuit, \(I=\frac{E}{R+r}=\frac{10}{9+1}=1 \mathrm{~A}\)

Potential difference across the two ends of the resistance R, V = IR = 1A x 9 Ω = 9 V and lost voltage =Ir= 1 A x 1Ω = 1 V

∴ If the work done to move a positive charge of 1 C through the resistance R and the cell are W₁ and W₂ respectively, then
W₁ = 9V x lC = 9J and W₂ =1V x 1C = 1J

Question 7. The resistivity of a material is 9 x 10^-6 Ω • cm. What is the length of a wire made of the same material with cross sectional area 0.5 cm² to have a resistance of 0.5 Ω?

Answer: The cross sectional area of the wire (A) = 0.5cm²
Resistivity of the material (ρ) = 9 x 10^-6 Cl • cm
Resistance (ft) = 0.5 Ω
Let the length of the wire = l

So,\(R=\rho \frac{l}{A}\) or, \(l=\frac{R A}{\rho}\)

∴ \(\begin{aligned}
l & =\frac{0.5 \times 0.5}{9 \times 10^{-6}} \\
& =27777.7 \mathrm{~cm}
\end{aligned}\) = 27777.7cm(approx).

Question 8. The ratio of the lengths, radii and resistivities of two metallic wires is 1:2 each. What is the ratio of the resistances of these two wires?

Answer: Suppose the length, the radius and the resistivity, of the first wire are , l₁,r₁ and ρ respectively. For the second wire, these are I₂, r₂ and p respectively.

\(\frac{l_1}{l_2}=\frac{r_1}{r_2}=\frac{\rho_1}{\rho_2}=\frac{1}{2}\)

 

Now, if the areas of cross section and the resistances of the two wires are A₁, R₁ and A₂, R₂ respectively, then

 

\(\frac{R_1}{R_2}=\frac{\rho_1 \frac{l_1}{A_1}}{\rho_2 \frac{l_2}{A_2}}=\frac{\rho_1}{\rho_2} \times \frac{l_1}{l_2} \times \frac{A_2}{A_1}=\frac{1}{2} \times \frac{1}{2} \times \frac{\pi r_2^2}{\pi r_1^2}\) \(=\frac{1}{4} \times\left(\frac{r_2}{r_1}\right)^2=\frac{1}{4} \times 2^2=1\)

 

∴ Ratio of the resistances of the wires is 1:1.

Question 9. When an electric cell with emf E and internal resistance r is connected to a resistance 12Ω, a current of 0.5 A flows in the circuit. When it is connected to a resistance of 25 Ω, the current is 0.25 A. Calculate the values of E and r.

Answer: In the first case, current  l₁ = 0.5 A

∴ \(\frac{E}{R+r}=\frac{E}{12+r}=0.5\) or, E = 0.5(12 + r) •••(1)

In the second case, current I₂ = 0.25 A

\(\frac{E}{25+r}=0.25\) = 0.25 or, E= 0.25(25 + r) •••(2)

By comparing equations (1) and (2), we get 0.5(12 + r) = 0.25(25 + r) or, 2(12 + r) = 25 + r
r = 1 Cl
Now from equation (1), we get E = 0.5(12 + 1) = 6.5 V

WBBSE Class 10 Revision Notes on Current Electricity

Question 10. A wire of resistance R is melted and then a new wire is made from that material Whose length is half of the first one. What is the resistance of the new wire?

Answer: Let the length of the original wire =1 and its cross sectional area =A. If the resistivity of the material of the wire = ρ, the resistance of the wire, \(R=\rho \frac{l}{A}\).

Now the length of the wire that is made by melting the original wire, l₁  =1/2

Let the cross sectional area of the new wire =AX As the volume of the wire remains unchanged,
l₁ A₁= lA  or,1/2. A₁= l.A or, A₁ = 2A

∴ Resistance of the new wire, \(R_1=\rho \frac{l_1}{A_1}=\rho \frac{\frac{1}{2}}{2 A}=\frac{1}{4} \times \frac{\rho l}{A}\) or, R₁ = R/4

Question 11. A copper wire of diameter 5 mm is made from a piece of copper. Another wire of diameter 1 cm is made from another piece of copper wire of the same mass. What is the ratio of the resistances of the two wires?

Answer: Diameter of the first wire (d₁) = 5 mm = 0.5 cm

∴ Cross sectional area of the first wire, \(A_1=\frac{\pi d_1^2}{4}\)

Diameter of the second wire (d₂) = 1 cm

∴ Cross sectional area of the second wire, \(A_2=\frac{\pi d_2^2}{4}\)

Let the lengths of the wires be l₁ and l₂ respectively. As the masses of the wires are the same, their volumes are also the same.
∴ A₁l₁ = Al₂

or, \(\frac{\pi d_1^2}{4} \cdot l_1=\frac{\pi d_2^2}{4} \cdot l_2\)

or, \(\frac{1}{l_2}=\left(\frac{a_2}{d_1}\right)^2=\left(\frac{1}{0.5}\right)^2=4\)

Now let the resistivity of copper =ρ and the resistances of the two wires are R₁ and R₂ respectively.

Then,\(R_1=\rho \frac{l_1}{A_1}\) and \(R_2=\rho \frac{l_2}{A_2}\)

\(\frac{R_1}{R_2}=\frac{\rho \frac{l_1}{A_1}}{\rho \frac{l_2}{A_2}}=\frac{l_1}{l_2} \times \frac{A_2}{A_1}=4 \times\left(\frac{d_2}{d_1}\right)^2\left[because \frac{l_1}{l_2}=4\right]\) = \(\)

∴ Ratio of the resistances of the two wires is 16: 1.

Question 12. Three resistances of values 1Ω, 2Ω and 3 Ω are connected in parallel. Calculate the equivalent resistance.

Answer: Let the equivalent resistance be R.

So, \(\frac{1}{R}=1+\frac{1}{2}+\frac{1}{3}=\frac{6+3+2}{6}=\frac{11}{6}\)

R = 6/11Ω.

Question 13. The equivalent resistances of two resistances in series and in parallel are 9Ω and 2Ω respectively. Calculate the values of the two.

Answer: Suppose the values of the two resistances are R₁ and R₂. The equivalent resistance of the resistances connected in series combination is 9Ω.

∴ R₁ + R₂ = 9 or, R₂ = (9-R₁) ••(1)

Again the equivalent resistance of the resistances connected in parallel combination is 2Ω.

∴ \(\frac{R_1 R_2}{R_1+R_2}=2 \quad \text { or, } \frac{R_1\left(9-R_1\right)}{9}=2\) [from equation (1)]

or, \(9 R_1-R_1^2\) = 18 or, \(R_1^2-9 R_1\) + 18 = 0 or, (R₁-3)(R₁-6) = 0

Now when (R₁ -3) = 0, then R₁ = 3 Ω and R₂ = 9-3 = 6Ω

Again, when (R₁-6) = 0, then R₁ = 6Ω and R₂ = 9-6 = 3Ω

∴ Value of these two resistances are 3Ωand 6Ω.

Question 14. A wire of resistance 10 Ω is divided into two equal parts and these two parts are put in a parallel combination. What is the resistance of the combination?

Answer: Resistance of the wire (R) = 10 Ω. As it is divided into two equal parts, resistance of each part, R₁= 10/2 = 5 Ω.

Now two resistances, each of 5Ω, are connected in a parallel combination. So the equivalent resistance R_P is given by

\(\frac{1}{R_p}=\frac{1}{5}+\frac{1}{5}=\frac{2}{5}\)

∴ R_p = 5/2 =2.5

Question 15. Three resistances; each of value R, are connected in series and parallel combination one after another. If the values of the equivalent resistances in the two cases are R_S and respectively, what is the value of \(\frac{R_S}{R_P}\)?

Answer: Equivalent resistance of the series combination of the three resistances, R_S = R + R + R = 3R and in case of parallel combination,

\(\frac{1}{R_p}=\frac{1}{R}+\frac{1}{R}+\frac{1}{R}=\frac{3}{R} \quad \text { or, } R_p=\frac{R}{3}\)

 

So,the required ratio, \(\frac{R_S}{R_P}=\frac{3 R}{\frac{R}{3}}=9\)

Question 16. Calculate the equivalent resistance between the points A and B in the circuit.

 

 

Answer: Equivalent resistance of the parallel combination of two resistances 6Ω and 4Ω,

\(R_1=\frac{6 \times 4}{6+4}=\frac{24}{10}=2.4 \Omega\)

 

Again, equivalent resistance of the parallel combination of two 8Ω and 3Ω,

\(R_2=\frac{8 \times 2}{8+2}=\frac{16}{10}=1.6 \Omega\)

 

Now, resistances R₁ and R₂ have formed a series combination.

∴ Equivalent resistance of these two resistance R₁ and R₂ in series id given by

R = R₁+ R₂ = 2.4 Ω + 1.6 Ω= 4Ω

∴ Equivalent resistance between the points A and B is 4 Ω.

Question 17. Calculate the value of I in the circuit.

 

 

Answer: Equivalent resistance R₁ of the parallel combination of two resistances 6 Ω and 4 Ω,

\(\frac{1}{R_1}=\frac{1}{6}+\frac{1}{4}=\frac{2+3}{12}=\frac{5}{12}\)

∴ R1 = 12/5 = 2.4

Now equivalent resistance of two resistances R₁ and 1.6 Ω connected in series combination is R = (2.4 + 1.6)Ω = 4Ω
Emf of the cell (E) = 5 V
Internal resistance (r) = 1Ω

∴ \(I=\frac{E}{R+r}=\frac{5}{4+1}=\frac{5}{5}=1 \mathrm{~A}\)

Current Electricity Topic C Heating Effect Of Electric Current, Electrical Power Synopsis

1. Joule’s law:
(1)First law: The amount of heat (H) produced in a conductor is directly proportional to the square of the current (l) passed, when the resistance (R) of the conductor and the time (t) of flow of current remain constant, i.e., H ∝ I² [when R and t remain constant].

(2)SecondLaw: The amount of heat(H) produced in a conductor is directly proportional to the resistance (R) of the conductor, when the amount of current (I) and the time (t) of flow of current remain constant, i.e.; H ∝ R [when I and t are constants].

(3)Third Law: The amount of heat (H) produced in a conductor is directly proportional to the time (t) for which the current passes, when the amount of current (I) and resistance (R) of the conductor remain constant, i.e., H ∝ t [when R and l are constants].

2. If a current l is sent through a resistance R for a time t, an amount of heat H is produced. Then according to Joule’s law, \(H=\frac{I^2 R t}{4.2} \mathrm{cal}\)

3. Electric Fuse: Electric fuse is a safety device which is used to limit the current in an electric circuit Fuse protects the circuit and the appliances connected in that circuit from being damaged. Generally an alloy of lead and tin (Pb 75%, Sn 25%) is used to make a fuse wire.

4. Electric energy: The capacity to do work by an electrical instrument is called its electric energy.
5. SI unit of electric energy is joule (J).
6. Electric power: Electrical power (P) of any electrically driven machine is defined as its rate of consumption of electrical energy with respect to time.

\(P=V I=I^2 R=\frac{V^2}{R}\)

7. Unit of electric power in SI is watt (W). 1W is defined as the rate of consumption of electrical energy in an electrical appliance when a current of 1A passes through the appliance at a potential difference of 1V.
1 kW = 10³ watt, 1 MW = 10⁶ watt

8. kW • h: The amount of electrical energy consumed by an electrical appliance of 1 kW power in Ih is called lkW • h or BOT unit.
1 kilowatt • hour -1000 x 3600 j = 3.6 X 10⁶ J

9. The rating of an electric bulb is 220 V -100 W. This means, that if the potential difference across the two ends of a iarnp is 220 V, it has the brightest glow and the lamp spends 100 j of electrical energy per second.
10. LED (Light Emitting Diode) lamp saves more electricity than CFL- (Compact Fluorescent Lamp). CFL produces around 7% to 9% of expended energy into visible light whereas LED produces nearly 4% to 18% of expended energy into visible light.

 

Current Electricity Topic C Heating Effect Of Electric Current, Electrical Power Short And Long Answer Type Questions

 

Question 1. Write down Joule’s laws of heating effect of electric current.

Answer:

Joule’s laws of heating effect of electric current:

In the year 1841, British physicist James Prescott Joule published three laws with respect to heating effect of electric current. These are:

1. Law of electric current: The amount of heat produced in a conductor (H) is directly proportional to the square of the current passed (I), when the resistance (R) of the conductor and the time of flow of current (t) remain constant, i.e., H ∝ I² [when R and t remain constant].

2. Law of resistance: The amount of heat produced in a conductor (H) is directly proportional to the resistance of the conductor (R), when the amount of current (l) and the time of flow of current (t) remain constant, i.e., H oc R [when / and t are constants].

3. Law of time: The amount of heat produced in a conductor (H) is directly proportional to the time for which the current passes (t), when the amount of current (I) and resistance of the conductor (R) remain constant, i.e. H ∝t [when R and I are constants].

Question 2. A steady current l is flowing through a resistance 8 connected in a circuit for time (t). Potential difference across its two ends is V. Answer the following questions.
1. If e is the charge of a single electron, then how many electrons do flow across any cross section of the resistor during that interval of time?
2. What is the work done in moving +Q charge potential difference across the potential difference V and what is the power supplied to circuit by the source?
3. What happens to the energy expended by the source? If the work done is totally converted into heat, then how much heat is produced In the resistor?

Answer:
1. Let n numbers of electron flow across any cross section of the resistor in time t.
So net charge flow, q=ne
Hence from the equation, l = q/t We get, q = It or, ne = It or, n = lt/e

2. Work done in moving +Q charge through a potential difference V is W = VQ ….(1)
Hence the power input to the circuit by the source is P = W/t = V .Q/t

3. Energy expended by the source gets dissipated in the resistor as heat.
Now, if the amount of heat produced is H, then from the law of equivalence of heat and work, we may write
W = JH or, H = W/J •••(2)

Hence from equations (1) and (2), we get

\(H=\frac{V Q}{J}=\frac{V I t}{J}=\frac{I^2 R t}{J}\)

where J = 4.2 J/cal is the mechanical equivalent of heat.

 

∴ \(H=\frac{I^2 R t}{4.2} \mathrm{cal}\)

Question 3. Electric current is passing through a metallic wire. How does the amount of heat that is produced according to Joule’s law, change for the following cases?
1. Value of electric current is tripled, keeping resistance and time of flow of current unchanged.
2. Potential difference across the two ends of the wire is doubled, keeping resistance and time of flow of current unchanged.

Answer: 1. According to Joule’s law, the amount of heat produced in a metallic wire is directly proportional to the square of the current passed, when the resistance of the conductor and time of flow of current remain constant. In this case, as the value of current is tripled, heat produced becomes 32 or 9 times.

2. Amount of heat produced is given by \(H=I^2 R t=\left(\frac{V}{R}\right)^2 R t=\frac{V^2 t}{R} \quad\left[because I=\frac{V}{R}\right]\)

So, amount of heat produced in a metallic wire is directly proportional to the square of the potential difference across the two ends of the wire, when the resistance of the conductor and time of flow of current remain constant. In this case, as the value of potential difference is doubled, heat produced becomes 2² or 4 times.

Question 4. What is the change in the lieat produced jp a conductor due to flow of current in the flowing two cases?
1. Current is allowed to flow in the opposite direction
2. ac is applied instead of dc.

Answer:
1. Heat produced in a conductor due to flow of current does not depend on.the direction of the current. If the magnitude of current and time of its flow through the conductor remain constant for a fixed resistance, then amount of heat produced does not change even if the direction of current is changed.

2. When ac is sent through a conductor instead of dc, then also heat is produced. If the magnitude of current and time of its flow through the conductor remain unchanged, then amount of heat produced in the conductor remains unchanged even if ac is applied instead of dc.

Question 5. Two resistances R₁ and R₂ are connected In parallel. This combination is connected to a circuit having a definite potential difference. and H₂ are the heat produced in them in-a time t. Prove that H₁ : H₂= R₂ : R₁.

Answer: Let us assume, thar l₁ and l₂ are the respective currents passing resistances R₁ and R₂ combination.

 

∴ ratio of heat produced in these two resistances in time t,

\(H_1: H_2=I_1^2 R_1 t: I_2^2 R_2 t=I_1^2 R_1: I_2^2 R_2\) \(\begin{aligned}
& =\frac{V^2}{R_1^2} \cdot R_1: \frac{V^2}{R_2^2} \cdot R_2 \cdot\left[because I=\frac{V}{R}\right] \\
& =\frac{1}{R_1}: \frac{1}{R_2}=R_2: R_1 \text { (proved) }
\end{aligned}\)

Question 6. What is electrical power? How is it measured?

Answer:

Electrical power:

1. Electrical power of any electrically driven machine is defined as the rate of consumption of electrical energy with respect to time.
2. When an electric current l is passed through an electrically driven machine for a time period t, then electrical energy consumed, W = VIt

where V is the potential difference between the two ends of the resistance of the instrument. Therefore, electrical power is given by

\(P=\frac{W}{t}=\frac{V I t}{t}=V I\) ….(1)

Again, if R is the resistance of the instrument, then according to the Ohm’s law, we get V=IR

So from equation (1), P =V1 = IR.I = I²R …(2)

Further, l =V/R

∴ \(P=\left(\frac{V}{R}\right)^2 R=\frac{V^2}{R^2} \cdot R=\frac{V^2}{R}\) ….(3)

Therefore from equations (1), (2) and (3), the electrical power is given by P = Vl + I²R +V²/R

Question 7. How is the rating of an electrical lamp done? Or, What do you mean by voltage rating and power rating of an electric lamp?

Answer: Any electrical appliance is manufactured in such a way that at a particular potential difference, it would be most effective without getting damaged. This value of potential difference is mentioned on the body of the appliance. This is called voltage rating.

If 220 V is written on the body of an electrical lamp, it indicates that the lamp, if connected to a 220 V supply line, would be most effective without getting damaged. If the potential difference is less than 220 V, it glows with less brightness and if the potential difference is more than 220 V, this lamp may get damaged or burnt.

In addition to voltage rating, there is another rating which is called power rating. This is also known as watt rating.
Power rating or watt rating is the electrical energy that is consumed per unit time by the electric lamp when a potential difference mentioned in the voltage rating is applied to it.

Question 8. Caiculate the resistance and the maximum current passing through a 220 V- 100 W lamp.

Answer: Rating of the lamp is 220 V-100 W. This means that when a potential difference V= 220V is applied across the two ends of the lamp, power consumed, P = 100 W.

If R is the resistance of the lamp, then \(P=\frac{V^2}{R}\) or \(R=\frac{V^2}{P}=\frac{220^2}{100}=484 \Omega\)

Again if l is the maximum current passing through the lamp, then
P=VI = or, I = P/V = 100/220 = 0.454A

Question 9. Two electric lamps of 240V-60W and 240 V-100 W are connected in series combination. Which one glows brighter?

Answer: If p electrical energy is consumed when a potential difference V is applied across the two ends of a lamp of resistance R, then

\(P=\frac{V^2}{R} \quad \text { or, } R=\frac{V^2}{P}\) ….(1)

So, resistance of the first lamp, \(R_1=\frac{240^2}{60}=960 \Omega\) and resistance of the second \(R_2=\frac{240^2}{100}=576 \Omega\)

Now, if the two lamps are connected in a series combination, the same current (I) flows through each lamp.
From Joule’s law, H ∝ I²Rt

Now as the resistance of first lamp is greater than that of the second lamp, more heat is produced in this case and so the first lamp glows brighter.

Question 10. Two filament bulbs of ratings 3 V-1 W and 3 V-2 W are connected in series and in parallel combination. In each case, which bulb does glow brighter?

Answer:
Resistance of 3V-1W bulb is given by \(R_1=\frac{3^2}{1}=9 \Omega\)

Resistance of 3V-2W bulb is given by \(R_2=\frac{3^2}{2}=\frac{9}{2}=4.5 \Omega\)

Case 1: When the bulbs are connected in series, current passing through them is the same. Here, the bulb which has greater resistance produces more heat and thus glows brighter. So, 3V-1W bulb glows brighter.

Case 2: When the bulbs are connected in parallel, potential difference across the two ends is the same. Here, the bulb which has less resistance produces more heat and thus glows brighter. So, the 3 V-2 W bulb glows brighter.

Question 11. There are two lamps of ratings 240 V- 500 W and 240 V -1000 W. Which one has got a thicker filament?

Answre: If P is the energy consumed when a potential difference V is applied across the two ends of a lamp of resistance R, then \(P=\frac{V^2}{R} \quad \text { or, } R=\frac{V^2}{P}\)  ……(1)

So, resistance of the first lamp, \(R_1=\frac{240^2}{500}\) = 115.2Ω  and resistance of the second lamp, \(R_2=\frac{240^2}{1000}=57.6 \Omega\) = 57.6Ω

Now, if the length (l) of conductor remains unchanged, A ∝ 1/R, where A is the cross sectional area of the conductor.

As the resistance of the second lamp is less, the cross sectional area of the filament of the second lamp is more, i.e., this filament is thicker than the filament of the first one.

Question 12. What happens if a 220 V-100 W lamp is connected to a 440V line? Further, what happens if it is connected to a 160 V line?

Answer:
1. When a 220 V-100 W lamp is connected to a 440V line, current greater than the highest admissible amount of current passes through it and as a result, huge amount of heat is produced and the coil of the lamp is burnt or damaged. So, the lamp glows brightly for a very short interval of time and then gets fused.
2. If the lamp is connected to a 160 V line, current lower than the highest admissible amount of current passes through it and as a result, the lamp glows less brightly.

Question 13. Describe an electric lamp and its working principle.

Answer:

An electric lamp

The practical application of the heating effect of electric current is best demonstrated in the case of an electric lamp. Two thick conducting wires are inserted in a sealed glass bulb. A long filament made of tungsten is attached to the two ends of the wires.

 

 

Now if current is passed through it, the filament gets extremely heated and emits light due to incandescence. As the melting point of tungsten is high (3380°C), it does not melt at high temperature. Again, to prevent it from corrosion, the bulb is filled with some inert gas like argon and in some cases, also with nitrogen gas. Nowadays, the filament is made up of wolframite (an alloy of iron, manganese and tungsten) instead of tungsten.

Question 14. Why Is an electric bulb filled with an inert gas or nitrogen instead of making It free from air or filling it up with air?

Answer: When an electric bulb is made free from air, its filament vaporises at high temperature. After a few days, the filament decays, disintegrates and then finally vaporises to form a coating inside the bulb.

As a result, the transparency of the glass is reduced and brightness of the bulb is decreased. On the other hand, if the bulb is filled with air, the filament will be corroded by oxygen of air to produce a metallic oxide at high temperature and the working power of the bulb is slowly reduced.

For all these reasons, an electric bulb is filled with an inert gas or nitrogen. Only then there is no possibility of corrosion and as vaporisation is very low, the bulb works for a longer period of time.

Question 15. Describe an electric lamp and its working principle.

Answer:

An electric lamp and its working principle:

In an electric heater, there is a notched roundshaped disc made of a bad conductor of electricity, like mica or fire clay, inside a metallic container. A long wire made of nichrome (an alloy of Ni, Cr and Fe) is set inside by twisting it like a spring. If the two ends of the nichrome wire are connected to an electric line with the help of a plug, the coil becomes hot and red.

 

 

As the resistivity of nichrome is high, it can be heated more and it is not corroded easily. Further, melting point of nichrome is high. For these reasons a nichrome wire is used in a heater. There is a base of porcelain on the mica or fire clay disc on which the cooking utensils are kept so that there is no possibility of connection between the cooking utensils and electricity.

Question 16. Though heat is generated continuously in an electric heater, its temperature becomes stable after sometime. What is the reason behind this?

Answer: When electrical current is passed through a heater, heat is produced in the coil of the heater according to Joule’s law and the temperature of the coil increases. As a result, difference of temperature between the coil and the surrounding goes on increasing.

More the difference of temperature, more is the rate of radiation of heat by the coil. In this way, the temperature of the coil increases and at a particular temperature, rate of production of heat in the coil is equal to the rate of radiation of heat by the coil, in this state, the temperature of the coil stops increasing further and becomes stable.

Question 17. What happens when a small length” of the coll of the nichrorne wire of a heater is cutoff?

Answer: When the length of the nichrorne wire is reduced, resistance of the coil also gets reduced. We know that different electrical appliances in our houses remain in parallel combination and due to this parallel combination, potential difference at the two ends of different electrical appliances always remain constant.

In this case, heat produced is inversely proportional to the resistance \(\).

Now as the resistance gets reduced in this case, so more heat is produced. Therefore, when the length of the coil made of nichrorne wire is reduced, more heat is produced.

Question 18. Describe an electric Iron and its working principle.

Answer:

Electric Iron

A nichrorne wire coil is fitted within two trianguler shaped mica sheets in an electric iron. This is kept securely in an iron covering. When current is passed through the coil, it gets heated and as a result, the iron covering also gets heated.

 

 

Question 19. What is a fuse? Write down the working principle of an electric fuse. Why is It used?

Answer:

Fuse:

1. Electric fuse is an arrangement that protects a circuit from excess flow of electric current. This is a type of wire with low melting point and is made of an alloy of tin and lead (tin 75%, lead 25%). The wire is joined with a holder made of porcelain and then connected to an electric line.

2. Electric fuse is connected in a series combination with the live wire of an electric line. The melting point of a fuse wire is low and it cannot carry current of a value more than that of a fixed value. Due to any reason, when value of current in that electric line increases suddenly such that its crosses that fixed value, the wire melts to disconnect the circuit. Thus, electric fuse saves electrical appliances from getting burnt or damaged.

3. Due to joining of a fuse wire in a line, costly electrical appliances in the house (for example, refrigerator, washing machine, TV etc.) are protected against damage in case of excess flow of electric current. Above all, possibility of a fire due to burning of a line by short circuit in the house is also considerably reduced.

Question 20. Make a comparative discussion on incandescent lamp, CFL and LED with respect to saving of energy.

Answer: In an incandescent lamp, nearly 98% of consumed electrical energy is converted to heat energy and only 2% produces visible light.

 

CFL (Compact Fluorescent Lamp) converts 7% to 9% of consumed energy into visible light whereas LED (Light Emilting Diode) converts nearly 4% to 18% of consumed energy into visible light. So, incandescent lamp does not save energy. CFL and LED save more energy than the incandescent lamp. Though CFL and LED are costlier than incandescent lamps, these reduce electric bill by saving a good deal of electrical energy in the long run.

Question 21. What are the main advantages of LED bulb in comparison to CFL?

Answer:

LED bulb is an energy-saver compared to CFL in many ways. Some of the main advantages of LED bulb are as follows:

1. LED bulb produces very low green house gas.
2. Consumption of energy is comparatively lower in LED bulb.
[For example, whereas a CFL of 12-15 W consumes 55 kW-h of energy in a particular time interval, an LED bulb consumes only 28 kW-h of energy in the same time interval.]
3. The light of an LED bulb goes out immediately when it is switched off but the same does not happen in case of a CFL.
4. The life of an LED bulb is many times more than that of a CFL. [For example, whereas one CFL can glow easily for 10000 hours, an LED bulb gives light for nearly 50000 hours.]
5. Light energy received from an LED bulb is much more than the same from one CFL of the same wattage.

Question 22. The coil of a heater does not radiate light whereas the filament of an electric lamp radiates light. Why?

Answre: The filament of an electric lamp is made of tungsten and is very thin. Again, the coil of a heater is made of nichrome whose area of cross section is more than the filament. As a result, the resistance of the filament of lamp is comparatively greater than the coil.

Due to its high resistance, the filament is heated more and after becoming white hot, it starts radiating light. But as the resistance of the coil of the heater is less, it is not heated to that extent and does not become white hot to radiate light.

Question 23. How is the energy rating mark of an electrical machine done? There are two washing machines manufactured by two different companies. Four stars are marked on one machine and five stars are marked on another. Which one is more economical in terms of consumption of electrical energy?

Answer:
1. The same machine of different models consume different amounts of electrical energy. To show this difference in consumption of electrical energy, some stars are marked on the machines. Amount of energy consumed by the machine can be compared by the number of stars.

More the number of these stars on the body of a machine, less is the amount of energy spent by that machine as compared to other models. Therefore more stars signify more savings. This is how energy rating mark of an electrical machine is done.

 

 

2. Five stars marked washing machines is more economical in terms of consumption of electrical energy.

Question 24. When we received the electric bill, we found that 24 units were consumed last month. What is the meaning of this unit? What is its name?

Answer:
1. The meaning of consumption of 24 units in the last month is that 24 BOT units of electrical energy were spent in that house last month. That is the unit of consumed electrical power.
2. The name of the unit is Board of Trade Unit (BOT unit) or kilowatt-hour (kW-h).

Question 25. What do you mean by a short circuit?

Answer:

Short circuit

When two electrical lines of opposite nature or two opposite poles of an electrical cell are connected through very low resistance, excessive amount of current flows in the circuit. This is called short circuit. As excessive amount of heat is produced in a short circuit, sometimes leading to a fire in the circuit or a damage to the circuit components.

Question 26. Define the unit of electrical power in SI.

Answer: The unit of electrical power in SI is watt (W).
1 W power: 1W is defined as the rate of consumption °f electrical energy in an electrical appliance When a current of 1 A passes through the appliance at a potential difference of 1V.

Question 27. What is W • h and kW • h or BOT unit? These are the units of which physical quantity?

Answer:
(1)1 W-h: The amount of electrical energy consumed by an electrical appliance of 1W power in 1 h is called 1W • h.

1 kW-h or BOT unit: The amount of electrical energy consumed by an electrical appliance of lkW power in lh is called lkW• h or BOT unit.

(2)W•h and kW• h or BOT unit are the unit of electrical energy.

Question 28. Express 1W • h and1 kW • h in J unit.

Answer: 1 W•h = \(1 \frac{\mathrm{J}}{\mathrm{s}}\) = 3600 J and 1 kW • h = 1000 W.h = \(1000 \frac{\mathrm{J}}{\mathrm{s}} \times 3600 \mathrm{~s}=3.6 \times 10^6 \mathrm{~J}\)

Question 29. MW and kW are the units of which physical quantity? Express MW in terms of kW.

Answer:
1. MW and kW are the practical units of electrical power.
2. 1 MW = 10⁶ W = 10³ • 10³ W = 1000 kW

Question 30. 220 V-100 W is written on the body of an electric lamp. What information does it convey?

Answer: If 200 V – 100 W is written on the body of an electric lamp, we can infer that if a potential difference of 220 V is applied across the two ends of the lamp, it will glow with maximum brightness and 100 J of electrical energy is consumed by the lamp every second.

Question 31. Why is the filament of an electric lamp made of tungsten?

Answer: Tungsten does not melt even at high temperatures as its melting point is 3380°C. In addition to this, as the resistivity of tungsten is high, the resistance of the wire is also high and thus it becomes very hot due to current flow to radiate light. Also, thin and long wire can be drawn from tungsten. For all these reasons, the filament of an electric lamp is made of tungsten.

Question 32. There are two thick conducting wires in an electric bulb at the ends of which the filament is attached. Why as light not emitted from them, even though the same amount of current passes through these wires?

Answer: As these two wires are short and their cross sectional area is large, the resistance is Sow. As the resistance is low, the heat produced is less in spite of passing the same amount of current. That is why no light is emitted.

Question 33. Why is a nichrome wire used in an electric heater?

Answer: Nichrome is an alloy of nickel, chromium and iron. As the resistivity of nichrome is high, so it can be heated more and as its melting point is also high (1400°C approx.), it will not melt so easily. Further, it does not corrode easily at high temperature. For all these reasons, a nichrome wire is used in a heater.

Question 34. What do you mean by a 10A fuse?

Answer:

10A fuse

A 10A fuse means that if an electric current of more than 10A passes through that fuse wire, the wire will become extremely hot and will melt immediately to disconnect the circuit. As a result, electric current through the circuit will stop flowing.

Word Problems on Current Electricity with Solutions

Question 35. The same amount of current is passed through one thin and another thick wire of the same material and of the same length for the same period of time. Heating of which wire will be more?

Answer: The resistance of a thin wire is more than that of a thick wire of the same material and of the same length. Now we know that, H = Therefore, the thin wire will become hotter than the thick wire when the same current is passed through it for the same period of time.

Question 36. Two wired of the same material and of the same cross sectional area are taken. The length of the first one is greater than that of the second. When the same amount of current is passed through both the wires for the same period of time, heating of which wire will be more?

Answer: Out of the two wires made of the same material and having the same cross sectional area, the one with greater length has higher resistance. Therefore the resistance of the first wire is more than that of the second wire. So, when the same amount of current is passed through both the wires for the same period of time, the first wire gets more heated.

Question 37. If same amount of electric current is passed for the same time duration through two copper wires-one thick and one thinheating of which wire will be more? Explain with reasons.

Answer: Between the two copper wire, the resistance of the thin wire is more. We know that if electric current and time of flow of current remain unchanged, then heat produced in the conductor is directly proportional to the resistance of the wire. Therefore, heat produced will be more in the case of the thin copper wife.

Question 38. Through two copper wires, one long and the other short, the same amount of current passed for the same duration of time. why the longer wire gets heated more? Explain with reasons.

Answer: The resistance of wires of the same cross section and made of the same materia! is directly proportional to the length of the wires. So, the resistance of the longer wire is more than the resistance of the shorter wire.

Now we know that the amount of heat produced in a conductor is directly proportional to the resistance of the conductor, when the amount of current and time of flow remain constant. Therefore, as the same amount of current is sent through both the wires for the same time duration, more heat is produced in the longer wire as its resistance is more. As a result, longer wire gets heated more.

Question 39. The same amount of current is passed through two wires of the same type for 1 minute and 5 minutes respectively. The heat produced in the second wire is how many times the heat produced in the first wire?

Answer: We know that the amount of heat produced in a conductor is directly proportional to the time of flow of current through the conductor when the amount of current and the resistance of the conductor remain constant.

As the same amount of current passes through these two wires of the same type and the time of flow in the second wire is 5 times the time of flow in the first wire, heat produced in the second wire is 5 times the heat produced in the first wire.

Question 40. Two wires of the same length but of different cross section and made of the same material are connected separately with a battery for a certain time. In which case is more heat produced?

Answer: We know that heat produced in a conductor,

\(H=\frac{V^\tau t}{4.2 \times R}\)

As V and t are constant, so, H ∝ 1/R

As the resistance of the thick wire is less than that of the thin wire, so more heat is produced when the thick wire is connected for the same time with the battery.

Question 41. Electricity is passing through a wire from east to west and it Is passing through another wire of the same resistance from west to east, is the amount of heat produced in these two wires during the same time duration equal?

Answer: The amount of heat produced in these two wires will be equal. This is because the heat produced in a conductor due to passing of electricity does not depend on the direction of current. Since both the wires have the same resistance and current flows through them for the same time duration, the amount of heat produced is also the same.

 

Current Electricity Topic C Heating Effect Of Electric Current, Electrical Power Very Short Answer Type Questions Choose The Correct Answer

 

Question 1. Keeping the resistance and time constant, if the amount of current is doubled, heat produced becomes

1. Two times
2. Four times
3. Six times
4. Eight times

Answer: 2. Four times

Question 2. When a number of resistances are kept in a parallel combination and the amount of current (l) and time of flow of current (t) remain constant, then the relation between the produced heat (H) and resistance (R) is

1. H ∝ R
2. H ∝ 1/R
3. H ∝ R²
   
4. H ∝ 1/R²

Answer: 2. H ∝ 1/R

Question 3. When the resistance (R) of a conductor and the time of flow of current (t) remain constant, then the relation between the heat produced (H) and the amount of current (l) is

1. H ∝ R
2. H ∝ 1/R
3. H ∝ R²
   
4. H ∝ 1/R²

Answer: 3. H ∝ R²

Wbbse Class 10 Physical Science Solutions

Question 4. When the resistance (R) of the conductor and the amount of current (I) remain constant, then the relation between the heat produced (H) and time (t) is

1. H ∝  t²
2. H ∝ t
3. H ∝ 1/t
4. H ∝ 1/t²

Answer: 2. H ∝ t

Question 5. When some resistances are kept in a series combination and the amount of current (I) and the time of flow of current (t) remain constant, the relation between the heat produced (H) and the resistance (R) is

1. H ∝ R
2. H ∝ R²
3. H ∝1/t
4. H ∝ 1/t²

Answer: 1. H ∝ R

Question 6. A fuse wire is made of

1. Tin
2. Lead
3. An alloy of tin and lead
4. An alloy of aluminium and copper

Answer: 3. An alloy of tin and lead

Question 7. Which of the following does not indicate 1 W (watt)?

1. 1 V x 1A
2. 1 A² x 1Ω
3. 1 V²/1Ω
4. 10V x 1Ω

Answer: 4. 10V x 1 Ω

Question 8. The resistance of a 240 V – 60 W lamp is

1. 480 Ω
2. 960 Ω
3. 240 Ω
4. 720 Ω

Answer: 2. 960 Ω

Question 9. What is the emf of the cell, if 10 J of work is done in moving 2 C of charge once around an electric circuit?

1. 10 V
2. 5 V
3. 2.5 V
4. 1 V

Answer: 2. 5 V

Question 10. Star sign on an electric machine indicates

1. Voltage rating
2. Watt rating
3. Energy rating
4. Ampere rating

Answer: 3. Energy rating

Question 11. Power consumed to send a current of 2 A through a potential difference of 5 V is

1. 20 W
2. 5 W
3. 10W
4. 15 W

Answer: 3. 10W

Question 12. Power consumed to send a current of 4 A through a resistance of 2 ft is

1. 64 W
2. 16 W
3. 24 W
4. 32 W

Answer: 4. 32 W

Question 13. Power consumed to maintain a potential difference of 10 V at the two ends of a resistance of 10 ft is

1. 10 W
2. 100 W
3. 1 W
4. 1000 w

Answer: 1. 10 W

Question 14. 0.2 W • h = how many joules?

1. 360
2. 720
3. 1080
4. 1440

Answer: 2. 720

Question 15. Which of the following bulbs has the highest resistance?

1. 220 V-25 W
2. 220 W-60 W
3. 220 V-100 W
4. 220 V-40 W

Answer: 3. 220 V-100 W

Question 16. Which of the following bulbs has the lowest resistance?

1. 220 V-25 W
2. 220 V-60 W
3. 220 V-100 W
4. 220 V-40 W

Answer: 3. 220 V-100 W

Question 17. When the following four bulbs are connected in series, which one will glow brightest?

1. 220 V-25 W
2. 220 V-60 W
3. 220 V-100 W
4. 220 V-40 W

Answer: 1. 220 V-25 W

Question 18. Among the following light emitters of equal watts, which one saves maximum power?

1. CFL
2. LED bulb
3. Incandescent bulb
4. Tube light

Answer: 2. LED bulb

Question 19. Electric iron works on the principle of

1. Action of magnet on electric current
2. Action of electric current on magnet
3. Action of electromagnetic induction
4. Production of heat due to flow of current

Answer: 4. Production of heat due to flow of current

Wbbse Class 10 Physical Science Solutions

Question 20. A constant potential difference is applied at the two sides of a uniform wire. Heat produced is doubled if

1. Radius of the wire is doubled
2. Both length and radius are doubled
3. Both length and radius are halved
4. Length is doubled but radius is halved

Answer: 3. Both length and radius are halved

Question 21. The resistance of a 220 V-100 W lamp is

1. 968 Ω
2. 1936 Ω
3. 484 Ω
4. 242 Ω

Answer: 3. 484 Ω

Question 22. A current of 1 A is passed through a resistance of 10 ft for 4.2 minutes. What is the amount of heat produced?

1. 500 cal
2. 600 cal
3. 700 cal
4. 800 cal

Answer: 2. 600 cal

Question 23. 1 kW = how many W?

1. 100
2. 1000
3. 500
4. 5000

Answer:

Question 24. 1 MW = how many W?

1. 10²
2. 10⁶
3. 10³
4. 10⁴

Answer: 2. 10⁶

Question 25. 1W • h = how many J?

1. 36
2. 360
3. 3600
4. 36000

Answer: 3. 3600

Question 26. Which one is the unit of power?

1. A • s
2. W • h
3. A²/ ohm
4. A² • ohm

Answer: 4. A² • ohm

Question 27. The amount of heat produced in a resistor when a current is passed through it can be found using

1. Faraday’s law
2. Ampere’s law
3. Joule’s law
4. Ohm’s law

Answer: 3. Joule’s law

 

Current Electricity Topic C Heating Effect Of Electric Current, Electrical Power Answer In Brief

 

Question 1. If H calories of heat is produced when a current of I A passes through a resistance of R Ω  for time t, then write the expression for H.
Answer: \(H=\frac{I^2 R t}{4.2} \mathrm{cal}\)

Question 2. If H joules of heat is produced when a current of I A passes through a resistance of R Ω for time t, then write the expression for H.
Answer: H = I²Rt J

Question 3. What is the step taken to prevent the corrosion of the filament of an electric bulb?
Answre: To protect the filament from oxygen in the air, the air in the bulb is either removed or replaced with an inert gas like neon or argon.

Question 4. What is a gas-filled bulb?
Answer: A bulb filled with an inert gas or nitrogen (N2) is called a gas-filled bulb.

Question 5. Between the filament and the fuse wire of an electric bulb, which one has greater cross section?
Answer: The cross section of a fuse wire is more than that of a filament of an electric bulb.

Question 6. What is the material used for making the heating coil of a heater?
Answer: The heating coil of a heater is made of an t alloy of Ni, Cr and Fe known as nichrome.

Question 7. What happens when there is a hole in the mica sheet of an electric iron?
Answer: There is possibility of getting an electric shock if there is a hole in the mica sheet of an electric iron.

Question 8. Which material is used for the manufacturing of an electric fuse?
Answer: An alloy of tin and lead (tin 25%, lead 75%) is used for the manufacturing of an electric fuse.

Question 9. What is the nature of the resistivity and the melting point of a fuse wire?
Answer: Both the resistivity and the melting point of a fuse wire are very low.

Question 10. What is the unit of electric power in SI?
Answer: The unit of electric power in SI is watt (W).

Question 11. What is the voltage at which a 220 V-100 W lamp glows with maximum brightness?
Answer: A lamp of 220 V-100 W glows with maximum brightness when the potential difference across it is 220 V.

Question 12. While purchasing an electrical appliance, which of the following factors should be given maximum importance? Voltage rating, watt rating, energy rating.
Answer: While purchasing an electrical appliance, the utmost importance should be given to energy rating.

Question 13. What is the amount of current passing through a 220 V- 100 W bulb connected across a potential difference of 200 V?
Answer: Amount of current passing through the lamp = 100/220 = 0.45A

Question 14. What is the commercial unit of electrical energy?
Answer: BOT unit is the commercial unit of electrical energy.

Wbbse Class 10 Physical Science Chapter 6 Question and Answers

Question 15. There are two bulbs of 220 V-100 W and 220 V-50 W respectively. Which one has more resistance?
Answer: The 220V-50W bulb has more resistance than the 220 V-100 W bulb.

Question 16. Write full form of CFL.
Answer: CFL stands for Compact Fluorescent Lamp.

Question 17. Which harmful element is used in CFL?
Answer: Mercury is used in CFL.

Question 18. What is the full form of LED?
Answer: The full form of LED is Light Emitting Diode.

Question 19. Between CFL and LED which have long lifespan?
Answer: Between CFL and LED, LED have long lifespan.

Current Electricity Topic C Heating Effect Of Electric Current, Electrical Power Fill In The Blanks

 

Question 1. The unit of electrical energy in SI is ______
Answer: Joule

Question 2. The value of the mechanical equivalent, of heat is _______
Answer: 4.2 J/cal

Question 3. An electric fuse saves us from accidents and short-circuits by ____ when an excess current flows through it.
Answer: Melting

Question 4. The filament of an electric bulb is made of ______
Answer: Tungsten

Question 5. The coil of the nichrome wire in an electric iron is covered with a _____ foil.
Answer: Mica

Question 6. 1 MW = _____ kW
Answer: 1000

Question 7. The unit of electrical power is multiplied by the unit of ____ to get an unit of electrical energy.
Answer: Time

Question 8. W • h is the unit ______
Answer: Electric Energy

Question 9. In a plant producing thermal electricity, plenty of ______ gas is emitted which pollutes the environment.
Answer: CO₂

Question 10. 1BOT unit = _______ W • h
Answer: 1000

Question 11. 1 W/A = 1 _____
Answer: V(volt)

Current Electricity Topic C Heating Effect Of Electric Current, Electrical Power State Whether True Or False

 

Question 1. In an electric cell, electrical energy gets converted into chemical energy.
Answer: False

Question 2. If the potential difference across the two ends of a wire is halved, keeping resistance and time of flow of current same, then the amount of heat produced will become 4 times.
Answer: False

Question 3. The filament of an electric bulb is made of tungsten.
Answer: True

Question 4. Lamps, electric fans and refrigerators used in our house are connected in series combination.
Answer: False

Question 5. CFL, LED lamps are more efficient than incandescent lamps.
Answer: True

Question 6. A fuse is used to avoid short circuit damage.
Answer: True

Question 7. If ac is passed through a conductor istead of dc, heat is not produced.
Answer: False

Question 8. 1 watt = 1 V x 1 A
Answer: True

Question 9. Maximum current that can passes through a 200V-25 W lamp is 1/8 A.
Answer: True

Question 10. Resistance of a 220 V-100 W lamp is 484Ω.
Answer: True

Question 11. Poisonous mercury vapour used in CFL.
Answer: True

Current Electricity Topic C Heating Effect Of Electric Current, Electrical Power Numerical Examples

 

1. If Q charge flows through a section under potential difference V, then the amount of electrical work done, W = QV
2. Heat evolved in a conductor of resistance R due to current flowing through it for time t, H =I²Rt (in J unit)

=\(\frac{I^2 R t}{4.2} \text { (in cal unit) }\)

3. If I be the current through resistance R and potential difference between its two ends is V then, electrical power

P = VI = I²R = \(=\frac{V^2}{R}\)

3. 1 BOT unit = 1kW • h = 3.6 x 10⁶ J
4. If rating of a electric lamp be xV-yW, then resistance of the filament of the lamp, R = \(\frac{x^2}{y}\) unit and current through the filament, I=y/x unit.

 

Question 1. How much heat Is produced if a current of 0.8 A passes through a resistance of 10 Ω for 1 minute?

Answer: Resistance of the conductor (R) = 10 Ω
Electric current (I) = 0.8 A
Time of flow of current (t) = 1 minute = 60 seconds

∴ Amount of heat produced in the conductor, H =  I²Rt = 0.8² X 10 X 60 = 384 J

∴ \(H=\frac{384}{4.2}\) cal = 91.42 cal 4.2

Question 2. There are two bulbs with ratings 220 V-40 W and 220V-60W.
1. Which one has greater resistance?
2. When the two bulbs are connected in series, which one glows more brightly?
3. When the two bulbs are connected in parallel, which one glows more brightly?

Answer:
1. We know, power (P) = \(\frac{V^2}{R} \text { or, } R=\frac{V^2}{P}\)
∴ Resistance of the 220 V-40 W bulb \(\left(R_1\right)=\frac{220^2}{40} \Omega\)

And resistance of the 220 V-60 W bulb 2202 \(\left(R_2\right)=\frac{22 U^2}{60} \Omega\)

2. When the two bulbs are connected in series, equal amount of current passes through each of them.

Therefore, power spent by the bulb of resistance R₁( P₁) = I² R₁ and power spent by the bulb of resistance R₂(P₂) = I² R₂
As R₁ >R₂, therefore P₁ > P₂. Again since heat produced, H α P, so the first bulb glows more brightly.

3. When the two bulbs are connected in parallel, the potential difference across the two ends of each of them is equal.

In that case, power consumed by the bulb of resistance \(R_1\left(P_1\right)=\frac{V^2}{R_1}\) and power consumed by the bulb of resistance \(R_2\left(P_2\right)=\frac{V^2}{R_2}\).

As R₁  > R₂, therefore, P₂ > P₁  and consequently, H₂ > H₁ [∴ H ∝ P]. Hence the second bulb glows more brightly.

Wbbse Class 10 Physical Science Chapter 6 Question and Answers

Question 3. The emf of an electric cell is 6 V and its internal resistance is 1Ω. The cell is connected to a resistance of 9Ω. How much heat is generated in the resistance in 21 seconds?

Answer: The emf of an electrical cell (E) = 6 V and its internal resistance (r) = 1Ω
Resistance in the external circuit (R) = 9 Ω
∴ Electric current in the circuit,

\(I=\frac{E}{R+r}=\frac{6}{9+1}=0.6 \mathrm{~A}[latex]

Heat produced in resistance R in t = 21 seconds is given by
[latex]H=\frac{l^2 R t}{4.2}=\frac{0.6^2 \times 9 \times 21}{4.2}=16.2 \mathrm{cal}\)

Question 4.6 bulbs of 40 W each, 4 fans of 80 W each, one TV of 100 W run daily for 5 hours in a house. What is the monthly (30 days) energy consumption of that house in BOT unit?

Answer: 1 kW • h = 1 BOT unit = 1 unit Light, fan and TV run daily for 5 hours.
∴ Power consumed = 40 x 6 + 80 x 4 + 100 = 660 W
∴ Electricity consumed in one day = 660 W x 5 h = 3300 W • h 3300

=\(\frac{3300}{1000}\) kW.h = 3.3 BOT unit.

∴ Electricity consumed in a month containing 30 days = 3.3 X 30 = 99 BOT unit.

Question 5. There are 1 light of 60 W, 2 lights of 100 W, 1 fan of 80 W and 1 heater of 1000 W in a house. If in the month of May, all lights burn for 6 h, fan runs for 12 h and heater burns for 4 h, what is the electric bill for that month? Cost of 1Bot Unit =  ₹ 5

Answer: The month of May contains 31 days.
Electricity consumption per day for electric lights, fan and heater = (1 X 60 X 6 + 2 X 100 X 6 + 1 X 80 X 12
+ 1 x 1000 x 4) W – h = 6520 W • h = 6.52 kW • h = 6.52 BOT unit
∴ Electricity consumption in the month of May = 6.52 x 31 = 202.12 BOT unit
Hence electricity bill for the month of May
= 202.12 x 5 =  ₹ 1010.60

Question 6. A 220 V-60 W lamp is connected to an electrical line with a potential difference of 220 V. What is the amount of current passing through the lamp? What is the resistance of the filament?

Answer: We know, watt = volt x ampere Suppose, a current l is passing through the lamp. So, 60 = 220 X I or, I = 60/220 = 0.27A

Now if the resistance of the filament of the lamp is R, we get V = IR or, 220 = 60/220 x R
\(R=\frac{220 \times 220}{60}=806.67 \Omega \text { (approx.) }\)

Question 7. What is the change of rate of production of heat, if the length and radius are both doubled by keeping the same potential difference across the two ends of a conducting wire?

Answer: Let the length of the wire = l and radius = r in the first case
∴ Cross sectional area, A = πr²

When the resistivity of the material of the wire is ρ, then resistance of the wire,  \(R=\rho \frac{l}{A}\)

Let V be the potential difference across the two ends of the wire, then rate of heat production,

\(H=\frac{V^2}{4.2 R} \mathrm{cal} / \mathrm{s}\) …..(1)

Now in the second case, the length of the wire, (l₁) = 2l and radius, (r₁) = 2r

∴ Cross sectional area, \(A_1=\pi r_1^2=4 \pi r^2=4 \mathrm{~A}\)

Now, resistance of the wire, \(R_1=\rho \frac{l_1}{A_1}=\rho \cdot \frac{2 l}{4 A}=\frac{1}{2} \times \frac{\rho l}{A}=\frac{R}{2}\)

Hence the change of rate of production of heat,

\(H_1=\frac{V^2}{4.2 R_1}=\frac{2 V^2}{4.2 \times R}=2 \mathrm{H}\)…(2)

∴ Rate of production of heat in the second case is double of that in the first case.

Wbbse Class 10 Physical Science Chapter 6 Question and Answers

Question 8. What Is the total electric bill for 30 days if an electric lamp of 220 V-100 W is lighted everydayfor 6 hours? Cost of lBQT unit = ₹5

Answer: Electrical energy consumed in one day = 100 x 6 = 600 W • h

∴ Electrical energy consumed in 30 days = 600 X 30 = 18000 W- h = 18 kW • h = 18 BOTunit
∴ Amount of electric bill = 5 x 18 = ₹90

Question 9. Two bulbs have ratings 240 V-500 W and 240V-1000W. Filament of which bulb is thicker?

Answer: Rating of the first bulb is 240 V-500 W.
∴ Resistance of the first bulb,

\(R_1=\frac{V_1^2}{P_1}=\frac{240 \times 240}{500}=115.2 \Omega\)

Rating of the second bulb is 240 V-1000 W.
∴ Resistance of the second bulb,

\(R_2=\frac{V_2^2}{P_2}=\frac{240 \times 240}{1000}=57.6 \Omega\)

Since R ∝1/A, when other parameters are kept A constant. A is area of cross section.

Hence resistance of the second bulb is less than that of the first.

∴ Area of cross section of the second bulb is greater than that of the first i.e., the filament of th second bulb is thicker than that of the first.

Question 10. An electric cell of emf 10 V and internal resistance 1 Ω is connected with a 3Ω resistor. What is the rate of production of heat by the cell?

Answer: emf of the cell (E) = 10 V
Internal resistance, r=1Ω
Resistance in the external circuit R = 3Ω

∴ Current through the circuit, \(I=\frac{E}{R+r}=\frac{10}{3+1}=2.5 \mathrm{~A}\)

Rate of production of heat by the cell =I²(R+r) = 2.5²(3+1) = 25J/s = 25/4.2 cal/s = 5.95 cal/s

Question 11. A lamp of resistance 440 Ω is used for 10 h in 220 V supply line. Find the amount of energy consume by the lamp in BOT unit.

Answer: Resistance of the lamp (R) = 440
potential difference, V = 220 V

∴ The amount of energy consumed  \(=\frac{V^2}{R} \cdot t=\frac{220^2 \times 10}{440 \times 1000} \mathrm{~kW} \cdot \mathrm{h}=1.1 \mathrm{~kW} \cdot \mathrm{h}\) =1.1Bot unit

 

Current Electricity Topic D Electromagnetism Synopsis

 

1. Ampere’s swimming rule: When a man swims along a current-carrying wire in the direction of the flow of current with his face turned towards the compass needle, then the north pole of the compass needle gets deflected towards his left hand.

2. Right hand grip rule: If a current carrying wire is held in the right hand such that the thumb points towards the direction of the flow of current, then the other fingers holding the wire indicate the direction of the magnetic lines of force.

3. Fleming’s left hand rule: If the thumb, forefinger and the middle finger of the left hand is held mutually perpendicular to each other in such a way that the forefinger points Electromagnetism to the direction of the magnetic field and the middle finger to the direction of the electric current, then the thumb indicates the direction of motion of the conductor or the direction of operative force on the conductor.

4. Barlow’s wheel: Barlow’s wheel is an arrangement to demonstrate action of magnet on current. Rotation of Barlow’s wheel can be explained using Fleming’s left hand rule.Electrical energy is converted into mechanical energy in Barlow’s wheel. Barlow’s wheel rotates only when direct current (dc) is pass.

5. If the direction of either the magnetic field or the electric current is reversed, the rotation of the wheel also gets reversed.
6. Speed of rotation of the wheel increases with the increase of
(1)Flow of current through the circuit,
(2)Intensity of the magnetic field. induction is the phenomenon in which an emf is induced in a coil if there is a change in the magnetic flux linked with the coil.

7. Faraday’s laws of electromagnetic induction:
(1)First law: When there is a change in the magnetic fiux linked with a dosed coil,fan electromotive force is induced In the coil, thereby producing electric current.

(2)Second law: in case of electromagnetic induction, the magnitude of the induced emf (electromotive force) is directly proportional to the time rate of change of magnetic flux linked with the coil.

(3)Lens’s law: in case of electromagnetic induction, the direction of the induced current (or emf) is such that the current opposes the very cause which produces it.

8. Fleming’s right hand rule: Stretch the thumb, middle finger and forefinger of your right hand In a mutually perpendicular way. If the forefinger of indicates the direction of magnetic field and the thumb indicates the direction of motion of conductor, then the middle finger will indicate the direction of induced current.

9. An electric motor is an electrical instrument where an electric-carrying coil rotates around a fixed axis under the influence of a fixed magnetic field and transforms electrical energy into mechanical energy.

10. Direct current and alternating current: If an electric current is always unidirectional then it Is called dc (direct current). if the direction of an electric current reverses at regular intervals, it is called ac (alternating current).

11. Advantages of ac over dc:
(1)The voltage of ac can be steped up or steped down as required by using step up or step down transformer respectively. But dc voltage can not be steped up or steped down.
(2)Production and distribution cost of ac is lower than that of dc.

12. Dynamo: Dynamo is an instrument by which mechanical energy is converted into electrical energy by utilising the principal of electromagnetic induction.

13. For domestic supply of electricity, two wires are drawn from the overhead or underground cable of the electric supply company. One is live wire and the other is neutral wire. In general, the live wire is covered with red plastic and the neutral wire is covered with black plastic. According to recent international guidelines, live wire is now covered with brown plastic and neutral wire is covered with light blue (sky blue) plastic.

 

Current Electricity Topic D Electromagnetism Short And Long Answer Type Questions

 

Question 1. Describe Oersted’s experiment to demonstrate the magnetic effect of electric current. Or, Show the magnetic effect of electric current with the help of a simple experiment.

Answer: Scientist Hans Christian Oersted performed an experiment in 1820 to demonstrate the magnetic effect of electric current. The following experiment is done on the basis of the same.

Required instruments: Two batteries of 1.5 V each, a thick copper wire, connecting wires, battery holder, switch, magnetic needle, resistor. Experiment: Two batteries are put in the battery holder and then connection is made as shown in Fig 30 with thick copper wire, resistor (R) and v switch through connecting wires.

The entire setup is kept by the side of a table. AB is the thick copper wire. Now wire AB is placed outside the table so that wire AB does not fall off or slide. Further, wire AB is kept such that A remains in the south and B in the north.

The magnetic needle is kept below the wire AB with the switch remaining off. In this state, magnetic needle remains along the direction of north-south. Now, when the switch is flipped on, it can be seen that the north pole of the magnetic needle is deflected towards the west.

 

 

Now, the poles of the batteries are interchanged. As a result, flow of current is from B to A in the wire AB or from north to south direction. As done previously, if the magnetic needle is kept below the wire AB, it is observed that the deflection of the north pole of the magnetic needle is towards east.

Conclusion: From this experiment of Oersted, we can conclude that a magnetic field is produced around a current carrying wire and if the direction of current is reversed, the direction of magnetic field is also reversed.

Question 2. In which direction does the deflection of the north pole of a magnetic needle take place when it has been kept below a current carrying wire in Oersted’s experiment, when the direction of current flow is from:
1. South to north
2. North to south

Answer:
1. When the direction of current flow through the wire is from south to north, then the north pole of the magnetic needle gets deflected towards west.
2. When the direction of current flow through the wire is from north to south, then the north pole of the magnetic needle gets deflected towards east.

 

 

Question 3. Explain the similarity between the magnetic fields created by a bar magnet and by the flow of current in a circular conductor.

Answer: The lines of force obtained in case of a bar magnet and in case of a circular current carrying conductorshow that a circular current carrying conductor is equivalent to a bar magnet since their lines of force are similar.

 

 

 

If the current flows in a clockwise direction in the circular conductor, the front face of the circular conductor acts like the south pole of a bar magnet.

 

 

If seen from the opposite side, the direction of flow is anticlockwise and that side acts like the north pole.

Question 4. If a current carrying circular coll is kept in a hanging position, what is the final alignment of the coil? Why?

Answer: When a current carrying circular coil is kept hanging, it settles such that its axis is along north-south direction. If we look at the coil from the south, flow of current is clockwise and if it is seen from the north, flow of current is anticlockwise. This is because a current carrying circular coil acts like a bar magnet.

 

 

The side from which the flow of current is found to be clockwise acts as the south pole and the side from which the flow of current is found to be anticlockwise acts as the north pole.

Question 5. Write down Fleming’s left hand rule.

Answer: According to Fleming’s left hand rule, if the thumb, the forefinger and the middle finger of the left hand is held mutually perpendicular to each other in such a way that the forefinger points to the direction of the magnetic field and the middle finger points to the direction of the electric current, then the thumb indicates the direction of motion of the conductor or the direction of the force acting on the conductor.

 

 

Question 6. Explain the working principle, construction and working of a Barlow’s wheel with a diagram.

Answer:
Working principle: A force acts on an electrical conductor due to the effect of magnetic field. In Barlow’s wheel, a star-shaped metal wheel with several spokes rotates continuously due to this force. Here, electrical energy is converted into mechanical energy.

Construction: A star-shaped copper wheel with several sharp teeth is mounted on a metal rod (B) in such a way that the wheel rotates along a horizontal axis in a perpendicular plane. The metal rod is attached with the wooden base by the help of a stand (T).

Just below the wheel and above the wooden base, a container filled with mercury (M) is placed in such a way that each tip of the tooth just dips into the container while rotating. The container (M) is placed in between the two poles of a horse-shoe magnet (NS). Now the axis of the wheel and mercury are connected to a battery and switch with the help of two binding screws (S₁ and S₂) and conducting wires.

Working: If the switch is flipped on, electric current passes along the path shown by arrows. Now, as the direction of the magnetic field and the direction of current through the wheel are mutually perpendicular to each other, so, according to Fleming’s left hand rule, a force is applied on the tooth of the wheel which touches mercury.

 

 

Due to this force, the wheel rotates towards right. Now as the wheel starts rotating, the tip of the tooth which is in contact with mercury rotates and the circuit gets disconnected. But due to the inertia of motion, the next tooth comes in contact with mercury and again the whole process continues and the wheel of Barlow’s wheel keeps rotating continuously.

Question 7. What happens to the rotation of Barlow’s wheel If:
1. The current flow is in opposite direction?
2. The two poles of the magnet are reversed?
3. The current flow is in opposite direction and the poles of the magnet are reversed simultaneously?
4. ac is applied instead of dc?

Answer:
1. If the current flows in the opposite direction- in a Barlow’s wheel, then by keeping the direction of magnetic field the same, the wheel starts rotating in the opposite direction.
2. If the current flows in the same direction but the two poles of the magnet are reversed, the Barlow’s wheel starts rotating in the opposite direction.
3. If the current flows in the Barlow’s wheel in the opposite direction and the two poles are reversed simultaneously, the Barlow’s wheel keeps rotating in the same direction.
4. If ac is applied instead of dc, the rotation of the Barlow’s wheel stops.

Question 8. Describe the construction and working of an electric motor.

Answer:
Construction: The main parts of an electric motor are:
1. Field magnet,
2. Armature,
3. Commutator and
4. Brush.

Answer:
1. Field magnet: This is a powerful horseshoe electromagnet. The strength of the magnet may be increased as required by increasing the amount of current or the number of wounds per unit length.

 

 

2. Armature: This is a rectangular coil ABCD made of insulated copper wire. The coil is wound on a soft iron bar. The coil is kept in such a way that the two arms of the coil; AB and CD are at right angles to the magnetic field.

3. Commutator: The two ends of the armature are joined with two half-rings E and F. (This is also called split-ring device.) This is called a commutator. When the armature rotates, these two half-rings also rotate.

4. Brush: The outer surfaces of the two half-rings touch two carbon brushes B₁ and B2. A battery and a switch are connected to these two brushes through conducting wires.

Working: When current is passed, it goes from A to B in the arm AB and from C to D in the arm CD. According to Fleming’s left hand rule, it is observed that the force acting on AB acts downwards and the force acting on CD acts upwards. Hence, the coil rotates anticlockwise. When the coil ABCD is vertical, then two brushes B₁ and B₂ come in the gap between the two halfrings E and F and connection is broken.

But due to inertia of motion, half-ring F touches brush B₁ and half-ring E touches brush B₂. As a result, direction of current in the arm AB is from B to A and in the arm CD, it is from D to C. In this state, according to Fleming’s left hand rule, the arm AB is deflected upwards and the arm CD is deflected downwards. In this way, current continues to flow in the circuit and the armature rotates in the same direction.

Question 9. What is the direction of magnetic field? How would you determine the direction of a magnetic field?

Answer:
1. The direction towards which a magnetic field exerts force on a small isolated north pole placed in it gives the direction of the magnetic field.
2. As it is not possible to get an isolated magnetic pole, so the deflection of the north pole of a magnetic needle is used to determine the direction of a magnetic field.

Question 10. When an electric current is passed through a conducting wire, does the wire get magnetised?

Answer: No, the wire does not get magnetised in this case. If we keep some iron filings on a piece of paper which is in contact with a conducting wire, we would find that the iron filings are not attracted by the wire.

Visual Representation of Electric Circuits

Question 11. Write down Ampere’s swimming rule.

Answer: According to Ampere’s swimming rule, if a man swims along the current carrying wire in the direction of the flow of current with his face always towards the compass needle, then the north pole of the compass needle gets deflected towards his left hand.

 

 

Question 12. Write down the right hand grip rule.

Answer: According to right hand grip rule, if a current carrying wire is held in right hand such that the thumb points towards the direction of flow of current, then the other fingers holding the wire indicate the direction of magnetic field lines.

 

 

Question 13. Can Barlow’s wheel he called a motor?

Answer: In an electric motor, electrical energy is transformed into kinetic energy. In Barlow’s wheel, electrical energy is transformed into rotational kinetic energy. Hence, Barlow’s wheel can be called an electric motor.

Question 14. How would you increase the speed of rotation of a Barlow’s wheel?

Answer: When the pole strength of the magnet or the amount of electric current increases, then the speed of rotation of Barlow’s wheel also increases.

Wbbse Class 10 Physical Science Chapter 6 Question and Answers

Question 15. When current is passed through a conducting circular coil, which magnetic pole is formed in which face?

Answer: South pole is formed on that face of the coil through which current flows in a clockwise direction, whereas north pole is formed on that surface of the coil through which current flows in an anticlockwise direction.

 

 

Question 16. What is an electric motor?

Answer:

Electric motor:

Electric motor is an electrical appliance where a current carrying coil rotates around a fixed axis under the influence of a uniform magnetic field and transforms electrical energy into mechanical energy.

Question 17. A dc motor is rotating clockwise. How is it possible to change this direction?

Answer: When the poie of the magnet is reversed or the direction of current is reversed, then the direction of rotation of a motor is also reversed, i.e., it rotaties in an anticiockwise direction.

Question 18. Write the uses of an electric motor. How would you increase the speed of rotation of the armature of an electric motor?

Answer:
1. Electric motor is used in electric fans, MP3 players, pumps, trains, rolling mills etc.
2. The speed of rotation of the armature can be increased by increasing the number of windings or increasing the current or increasing the strength of the magnetic field.

Question 19. The north Pole and the south pole of a magnetic needle are not indicated. How would you identifythe poles ofa magnetwith the help of a conducting wire and a battery?

Answer: The conducting wire is connected to the battery. Now, the wire is kept in such a way that the electric current in the wire flows from south to north. If the magnetic needle is then kept below the wire, the pole that gets deflected towards the west is the north pole. The remaining one is the south pole.

Question 20. The positive terminal and the negative terminal of a battery are not indicated How would you identify the terminals of the battery with the help of a conducting wire and a magnetic needle?

Answer: Generally the magnetic needle aligns itself in the north-south direction. The conducting wire is connected with the battery and is placed along
the north-south direction. Now, the magnetic needle is kept below the wire. If the north pole is deflected towards west, then the wire at the south end has been connected with the positive terminal and if the north pole is deflected towards east, then the wire at the, south end has been connected with the negative terminal.

Question 21. What is the function of caron in dc motor?

Answer:

The function of caron in dc motor:

Carbon brushes make contact with the commutator to supply current to the armature in on brushes motor.

 

Current Electricity Topic D Electromagnetism Very Short Answer Type Questions Choose The Correct Answer

Question 1. Electrical energy is produced from mechanical energy in

1. Barlow’s wheel
2. Electric motor
3. Electric generator
4. Transformer

Answer: 3. Electric generator

Question 2. Barlow’s wheel rotates when

1. dc is passed
2. ac is passed
3. ac or dc is passed
4. No current is passed

Answer: 1. dc is passed

Question 3. Barlow’s wheei is a

1. Simple dc motor
2. Simple ac motor
3. dc generator
4. ac generator

Answer: 1. Simple dc motor

Question 4. The liquid used in the arrangement of Barlow’s wheel is

1. Glycerin
2. Alcohol
3. Mercury
4. Kerosene

Answer: 3. Mercury

Question 5. Which of the following converts electrical energy into mechanical energy?

1. Dynamo
2. Transformer
3. Electric motor
4. Inductor

Answer: 3. Electric motor

Question 6. Rotation speed of the armature of a motor can be increased by

1. Increasing current intensity
2. Increasing number of turns of the coil
3. Increasing the strength of the magnetic field
4. All of these

Answer: 4. All of these

Question 7. According to Fleming’s left hand rule, the middle finger indicates the direction of

1. Magnetic field
2. Current
3. Motion
4. Force

Answer: 2. Current

Question 8. Rotation of Barlow’s wheel occurs according to

1. Fleming’s left hand rule
2. Ampere’s swimming rule
3. Right hand grip rule
4. Fleming’s right hand rule

Answer: 1. Fleming’s left hand rule

 

Current Electricity Topic D Electromagnetism Answer In Brief

 

Question 1. What can be determined with the help of Ampere’s swimming rule?
Answer: The direction of the magnetic field around a long wire carrying electric current can be determined with the help of Ampere’s swimming rule.

Question 2. When a man swims towards east, what is the direction of deflection of the north pole of the magnetic needle according to the Ampere’s swimming rule? [Suppose the current flows from west to east.]
Answer: There is no deflection of the north pole of the magnetic needle.

Question 3. According to Ampere’s swimming rule, in which direction a man should swim for the deflection of the north pole of a magnetic needle to be towards west. [Suppose the current flows from south to north.]
Answer: The man should swim from south towards north.

Question 4. In a magnetic field, when a force acts on the south poje of a magnet towards the east direction, then what is the direction of the magnetic field?
Answer: The direction of the magnetic field is towards the west.

Question 5. Would two magnetic lines of force intersect each other?
Answer: No, two magnetic lines of force wouuld never intersect each other.

Question 6. Can ac (alternating current) rotate a Barlow’s wheel?
Answer: No, an ac cannot rotate a Barlow’s wheel.

Question 7. What is magnetic flux?
Answer: The number of magnetic lines of force passing perpendicularly through a plane placed in a magnetic field is called magnetic flux.

Question 8. What type of electric current can rotate a Barlow’s wheel?
Answer: dc (direct current) can rotate a Barlow’s wheel.

Wbbse Class 10 Physical Science Chapter 6 Question and Answers

Question 9. What type of energy transformation does take place in an electric motor?
Answer: Electrical energy is transformed into mechanical energy in an electric motor.

Question 10. What type of energy transformation does take place in a dynamo?
Answer: Mechanical energy is transformed into electrical energy in a dynamo.

Question 11. Between thermal energy and hydroelectric energy which one is renewable?
Answer: Hydroelectric energy is renewable energy

Question 12. How do you determine the direction of rotation of Barlow’s wheel?
Answer: The direction of rotation of Barlow’s wheel is determined by Fleming’s left hand rule.

Question 13. When the south pole of a bar magnet is brought towards a closed coil along its axis, what is the direction of current in the front face of the coil?
Answer: The direction of current in the front face of the coil is clockwise.

Question 14. Name the device which is used to reverse the direction of current in the coil of a motor after every half rotation.
Answer: Commutator.

Question 15. State the function of a split ring in a dc motor.
Answer: Function of split ring in a dc motor is to reverse the direction of current in the coil of a motor after every half rotation.

 

Current Electricity Topic D Electromagnetism Fill In The Blanks

 

Question 1. In Fleming’s left hand rule, the forefinger indicates the direction of ______
Answer: Magnetic Field

Question 2. Magnetic lines of force emerge from the ______ pole of a magnet.
Answer: North

Question 3. When an electric current is passed through a conducting wire, a _________ field is produced around it.
Answer: Magnetic

Question 4. When current is flowing through a conductor, the conductor is not ______
Answer: Magnetised

Question 5. For a circular current carrying loop, the face of the coil in which current appears clockwise develops ______ pole.
Answer: North

Question 6. If ac is passed through a dc motor, its armature does not ______
Answer: Rotate

Question 7. Magnetic lines of forces may be _____ curve.
Answer: Closed

Current Electricity Topic D Electromagnetism State Whether True Or False

 

Question 1. Direaction of rotation of Barlow’s wheel is determined by right hand grip rule.
Answer: False

Question 2. A static charge may produce mgnetic field.
Answer: False

Question 3. The direction of magnetic field at any point on a magnetic line of force is along the tangent drawn on that point.
Answer: True

Question 4. In right hand thumb rule the thumb indicates the direction of flow of urrent.
Answer: True

Question 5. A circular wire carrycing current acts as a bar magnet.
Answer: True

Question 6. Magnetic field intensity inside a spiral current carrying conductor increases when an iron rod is placed inside the coil.
Answer: True

Question 7. Strength of an electromagnet can be increased as much as desired.
Answer: False

Question 8. Galvanometer is an electrical device which is based on the principle of magnetic effect of electric current.
Answer: True

Question 9. The magnitude of force applied on a long straight current carrying wire is maximum when it is placed perpendicular to the direction of magnetic field.
Answer: True

Question 10. Direction of the magnetic field around a long wire carrying current is determined by right hand thumb rule.
Answer: True

 

Current Electricity Topic E Electromagnetic Induction And Domestic Electrical Circuit Synopsis

 

1. Electromagnetic induction is the phenomenon in which an emf is induced in a coil if there is a change in the magnetic flux linked with the coil.

2. Faraday’s laws of electromagnetic induction:

3. First law: When there is a change in the magnetic fiux linked with a dosed coil, an electromotive force is induced in the coil, thereby producing electric current

Wbbse Class 10 Physical Science Chapter 6 Question and Answers

Second law: In case of electromagnetic induction, the magnitude of the induced emf (electromotive force) is directly proportional to the time rate of change of magnetic flux linked with the coil.

4. Lenz’s law: In case of electromagnetic induction, the direction of the induced current (or emf) is such that the current opposes the very cause which produces it.

5. Fleming’s right hand rule: Stretch the thumb, middle finger and forefinger of your right hand in a mutually perpendicular way. If the forefinger of indicates the direction of magnetic field and the thumb indicates the direction of motion of conductor, then the middle finger will indicate the direction of induced current.

6. Direct current and alternating current: If an electric current is always unidirectional then it is called dc (direct current). If the direction of an electric current reverses at regular intervals, it is called ac (alternating current).

7. Advantages of ac over dc:
(1)The voltage of ac can be steped up or steped down as required by using step up or step down transformer respectively. But dc voltage can not be steped up or steped down.
(2) Production and distribution cost of ac is lower than that of dc.

8. Dynamo: Dynamo is an instrument by which mechanical energy is converted into electrical energy by utilising the principal of electromagnetic induction.

9. For domestic supply of electricity, two wires are drawn from the overhead or underground cable of the electric supply company. One is live wire and the other is neutrai wire. In general, the live wire is covered with red plastic and the neutral wire is covered with black plastic. According to recent international guidelines, live wire is now covered with brown plastic and the neutral wire is covered with light blue (sky blue) plastic.

 

Current Electricity Topic E Electromagnetic Induction And Domestic Electrical Circuit Short And Long Answer Type Questions

 

Question 1. Write down Faraday’s electromagnetic induction. Or, Write down the two laws of Faraday regarding electromagnetic induction.

Answer:
First law: Whenever there is a change in the magnetic flux linked with a closed coil, an electromotive force is induced in the coil. The induced emf lasts as long as the magnetic flux continues to change.

Second law: In case of electromagnetic induction, the magnitude of the induced emf (electromotive force) is directly proportional to the rate of change of magnetic flux linked with the coil.

Question 2. State Lenz’s law. Explain Lenz’s law with tHe help of the law of conservation of energy.

Answer:
1. According to Lenz’s law, the direction of any magnetic induction effect is such as to oppose the cause of the effect.
2. Let us assume that the N pole of a bar magnet is brought near a closed coil along its axis and due to this, the direction of induced current in the coil is clockwise. That means, S pole is formed in the front face of the coil.

This S pole attracts the N pole of the bar magnet. As a result, the bar magnet accelerates towards the coil. In this case, it is found that without the supply of any external energy, kinetic energy of the magnet and also electrical energy are obtained which go against the principles of law of conservation of energy.

Therefore, when the N pole of the bar magnet proceeds along the axis of the coil, then flow of current in the coil is anticlockwise. As a result, N pole is created in the front face of the coil instead of S pole and it repulses the N pole of the bar magnet.

To move the bar magnet towards the coil along its axis, some mechanical work has to be done. This mechanical work is converted into electrical energy. Therefore, the direction of the induced emf is such that it opposes the very cause responsible for its production—this is Lenz’s law.

Question 3. Show that Lenz’s law supports the law of conservation of energy

Answer: It is known from the phenomenon of electromagnetic induction that if there is a relative motion between a magnet and a coil, a current is induced in the coil. It has been found by experiment that if the magnet is brought near or taken away from the coil, some resistance acts always.

As a result, in order to maintain a relative motion between the magnet and the coil, positive work has to be done against this resistance. This work is manifested as electrical energy in the coil. In other words, the law of conservation of energy is valid in this case.

Lenz’s law states that the direction of induced emf is such that it opposes the cause responsible for its production. Hence, Lenz’s law supports the law of conservation of energy.

Question 4. By keeping a copper ring horizontal, a bar magnet is dropped freely from a steep height through the centre of the ring, is the acceleration of the failing ring equal to or more than the acceleration due to gravity?

Answer: When the bar magnet is dropped from a steep height towards the centre of the copper ring, then magnetic flux linked to the copper ring increases, that is, there is a change of magnetic flux linked to the copper ring. As a result, an electromotive force is induced in the ring and electric current starts to flow.

The direction of induced current is such that it opposes the very cause which produces it. In this case, the fall of the bar magnet is opposed. Therefore, a repulsive force acts upward on the bar magnet so that it falls downwards with lesser acceleration than the acceleration due to gravity.

Question 5. What do you mean by direct current and alternating current?

Answer:
Direct current (dc): When the direction of an electric current is always the same, it is called dc.

Alternating current (ac): When the direction of an electric current reverses at regular intervals, it is called ac.

Change of electric current (I) is shown with change of time (t) with the help of a graph.
The direction of current does not change but in the direction of current reverses at regular intervals. So current is dc and it is ac.

 

 

Question 6. What are the advantages of ac over dc?

Answer:

The advantages of ac over dc are as follows:

1. With the help of a transformer, ac may be transformed from low voltage to high voltage (step-up transformer) and from high voitage to low voltage (step-down transformer). This advantage is not available in case of dc. i The cost of generation of ac by a generator is less than that of dc.
2. Loss of energy while transmission comparatively less in ac

Question 7. Discuss the working principle of an ac dynamo in brief.

Answer:

The working principle of an ac dynamo in brief:

The main parts of an ac dynamo are shown. The main parts are field magnet, armature, slip ring and brush. N and S are the two poles of a horse-shoe magnet, which is called a field magnet. But, generally, an electromagnet is used in place of a field magnet as a permanent magnet.

This field magnet creates a nearly constant magnetic field between the two poles, directed from north pole to south pole. ABCD is a rectangular coil made by winding insulated copper wires on a rectangular bar made of soft iron. This is called an armature.

The open ends of the armature coil are connected with two perfectly smooth round-shaped rings made of with two perfectly smooth round-shaped rings made of result, electromotive force is induced in the coil and current flows in the circuit.

 

 

When the arm AB of the coil ABCD comes down, then the direction of current in the resistance R becomes opposite to the direction of the current when the arm AB goes up. Hence, during one full rotation of the coil ABCD, the direction of current in the resistance R changes twice.

In this way, as the coil ABCD rotates with a uniform angular velocity, the direction of current in the resistance changes direction periodically at a fixed interval of time and the generated current is ac in nature.

Question 8. Discuss the working principle of a dc dynamo in brief.

Answer:

The working principle of a dc dynamo in brief:

The main parts of a dc dynamo are shown. The main parts are field magnet, armature, commutator and brush. N and S are two poles of a horseshoe magnet, which is called a field magnet. But, in general, an electromagnet is used in place of a field magnet as a permanent magnet. This field magnet creates a nearly constant magnetic field between the two poles, directed from north pole to south pole.

ABCD is a rectangular coil made by winding insulated copper wires on a soft iron cylindrical bar. This is called an armature. The open ends of the armature coil are connected with two semi-circular sheets R₁  and R₂ made of brass. R₁  and R₂ together form a commutator. When the coil rotates, the commutator also rotates. B₁ and B2 are two carbon brushes.

When the coil AB rotates with the commutator, then the brushes touch the two sheets of the commutator lightly. A resistance R is connected with the brushes B₁ and  B₂ in the external circuit. Now when the coil rotates, magnetic flux linked with the coil changes. As a result, electromotive force is induced in the coil and current flows in the circuit.

When current is passed through the coil in the direction of ABCD, then applying Fleming’s left hand rule we can say that the arm AB experiences a downward force while arm CD experiences an upward force. After crossing the vertical position, the arm AB tries to move upwards and the arm CD tries to come downwards due to inertia of motion. At that time, sheet R₁ comes in contact with brush  B₂ and sheet R₂ comes in contact with brush Br.

As a result, the current is unidirectional instead of rotating in the opposite direction. Thus, it flows through the armature. The open ends of the armature coil are connected with two semi-circular sheets R₁ and R₂ made of brass. R₁  and R₂ together form a commutator. When the coil rotates, the commutator also rotates. B₁ and B₂ are two carbon brushes.

When the coil AB rotates with the commutator, then the brushes touch the two sheets of the commutator lightly. A resistance R is connected with the brushes B₁ and B₂  in the external circuit. Now when the coil rotates, magnetic flux linked with the coil changes. As a result, electromotive force is induced in the coil and current flows in the circuit.

When current is passed through the coil in the direction of ABCD, then applying Fleming’s left hand rule we can say that the arm AB experiences a downward force while arm CD experiences an upward force. After crossing the vertical position, the arm AB tries to move upwards and the arm CD tries to come downwards due to inertia of motion.

At that time, sheet R₁ comes in contact with brush  B₂ and sheet R₂ comes in contact with brush Br. As a result, the current is unidirectional instead of rotating in the opposite direction. Thus, it flows through the resistance R in the same direction in the external circuit and dc is generate.

 

 

Question 9. Write down the difference between a dynamo and an electric motor.

Answer:

The diffrence between a dynamo and an electric motot as follows:

Dynamo	Electric motor
1. Mechanical energy is converted into electrical energy in a dynamo	1. Electrical energy is converted into mechanical energy in an electric motor.
2. Dynamo is constructed on the basis of the principle of electromagnetic induction.	2. Electric motor is constructed on the basis of the magnetic action of electric current.

 

Question 10. Describe, in brief, the principle generation of thermal electricity.

Answer:

Principle generation of thermal electricity

In a simple turbine, some blades are attached to the end of a rod which is connected to the coil of a dynamo. If the turbine is rotated, the coil also rotates and electrical energy is generated

In a thermal power station, water is boiled by burning coal or any other fuel and transformed into steam. This steam rotates the blades of a turbine and consequently, the armature coil of the dynamo rotates.

 

 

As a result, there is a change in the magnetic flux linked with the coil and an electromotive force is induced. Thermal electricity is generated in this way.This steam is again condensed in a condenser and is sent back by Rankine cycle to the place where it is heated.

Question 11. Briefly describe the principle of generation of hydroelectricity

Answer:

The principle of generation of hydroelectricity:

In a hydroelectric power plant, water is stored in reservoirs. Now this water stored at a great height is allowed to fall downwards. As the mass of water falls down, its potential energy decreases and kinetic energy increases.

If a blade of a turbine is kept in this falling water, it rotates and the armature coil of the dynamo also rotates with it. As a result, there is a change in the magnetic flux linked with the coil causing an electromotive force to be induced and thus hydroelectricity is generated.

Huge amount of CO₂ is generated in a thermal power plant which pollutes the environment. For this reason, many countries of the world are now giving importance to hydroelectricity. At present, 16% of the total generated electricity is hydroelectricity.

Question 12. Explain the arrangement of electric fine in a house with diagram.

Answer:

The arrangement of electric fine in a house with diagram:

For domestic supply of electricity, two wires are drawn from the overhead or underground cable of the electric supply company. One is live wire and the other is neutral wire. In general, live wire is covered with red plastic and neutral wire is covered with black plastic. According to international guidelines, live wire is now covered with brown plastic and neutral wire is covered with light blue (sky coloured) plastic.

Live wire and neutral wire are first connected with the meter. Now, the live wire is passed through the main fuse and neutral wire is taken directly from the meter and connected with the main switch. The line of the house can be switched ‘on’ and ‘off’ as per requirement with the help of the main switch.

As the potential difference between the earth and the neutral line is not always zero, an iron rod is inserted inside the ground and that rod is connected with the conducting wire. This arrangement is called earthing and the wire used for this is called the earth wire. The earth wire is green or yellow in colour.

The earth wire is taken to the switch board meant for electrical appliance (iron, refrigerator, table fan etc.) through the main switch. Live wire goes to different switch boards from the main switch through several branch lines. Points are made, according to requirement,in the switch board for use of fan, tv, lamp etc.

Live wire is connected to each switch board through, a fuse. Next, the wiring of the house is done from switch board through live wire and neutral wire. Lamp, refrigerator, electric fan etc., in the house remain in a parallel combination.

 

 

Question 13. What is earthing? Why is it done? How earthing is done?

Answer:

Earthing:

1. Connecting an electrical circuit or an electrical appliance to the earth through a conducting wire is known as earthing.
2. Due to any defect in the electrical connection, the metal coating of the appliance may get electrified. There is a possibility of danger due to that. If anybody standing on the ground touches that appliance, the person may get an electric shock. Earthing is done to avoid that possibility.

3. For earthing, a conducting rod made of metal is driven into the ground. In the household circuit, there is an extra wire (earthing wire) connected to this rod. In case of a three-pin socket, the comparatively thicker hole is connected to this wire.

The resistance of this wire is very low There is a connection between the metal coating of the electrical appliance and the earthing wire. The potential of the earth is zero. So, if anyhow the coating of the instrument is electrified, that electricity goes to the earth directly. Therefore the possibility of getting a shock is minimised.

Question 14. Explain the functioning of a switch and a main switch.

Answer:

The functioning of a switch and a main switch:

Switch is an arrangement in an electrical circuit by which the flow of electric current can be made ‘off’ and ‘on’. Switch is generally made of ebonite and is fixed on the respective board attached on the surface of the wall. Generally, a 5A switch is used in the circuit of electric fan, bulb, tubelight and a 10A or 15A switch is used in the circuit of pump, refrigerator, heater.

 

 

Main switch is an arrangement which may be made ‘off’ and ‘on’ according to necessity to disconnect or connect the electric line of the house from the main electric supply line. As a result, the flow of electric current in homes can be stopped or started according to one’s will.

 

 

Question 15. What are electromagnetic induction and induced current?

Answer:

Electromagnetic induction and induced current

If there is change of magnetic flux associated with a closed coil, an electric current originates in the coil. This phenomenon is called electromagnetic induction and the current flowing in the coil is called induced current.

Question 16. What is induced electromotive force?

Answer:

Induced electromotive force

If there is a relative motion between a magnetic field and a conductor, then an electromotive force originates in the conductor which is called induced electromotive force.

Question 17. The north poles of two identical bar magnets are kept at the same height from the centres and at right angles to the planes of two identical closed circular conducting coils. Now both the bar magnets are brought near the coils to the same height, first one rapidly and the second one slowly. In which case is the induced current more

Answer: Induction of current is more in the first coil because the first magnet was brought rapidly and thus, the rate of change of magnetic flux linked with the first coil is more than the second one. As result, the amount of induced electromotive force is also more. Hence, induction of current is more in the first case.

Question 18. Along the axis of a circular coil made of wire, a cylindrical bar magnet Is kept. The fragment rotates about the axis. Is there any induction of current in that coil?

Answer: When the magnet rotates about the common axis of the magnet and the circular coil, there is no change in the flux linked to the coil. So, no electromotive force is induced in the coil. As a result, no current is induced in the coil.

Question 19. A bar magnet is kept along the axis of a circular conducting coil. Now both the coil and the bar magnet are moved in the same direction with the same velocity. Is there any induction of current in the coil?

Answer: When both the coil and the bar magnet are moved in the same direction with the same velocity, there is no relative velocity between them. As a result, there is no change in the magnetic flux linked to the coil. Therefore, no electromotive force is induced and thus, no current is induced in the coil.

Question 20. What is a dynamo? How many types of dynamo are there? Name them.

Answer:

Dynamo

1. Dynamo is a device in which mechanical energy is converted into electrical energy by utilising the principle of electromagnetic induction.
2. It is of two types: (1) ac dynamo and (2) dc dynamo.

Question 21. What is the combination in which electric lamp, electric fan, refrigerator etc. are connected with the electric line of house? Why?

Answer: Electric lamp, electric fan, refrigerator etc. are connected in a parallel combination with the electric line of a house because any one of them can be switched on or off as per requirement and the potential difference across the two ends of every electrical appliance remains constant.

Question 22. Write down the formation of a three-pin plug in brief.

Answer:

Formation of a three-pin plug in brief

In a three-pin plug, there are three metal pins. The top one is longer and thicker than the other two which are of equal size. The two lower pins are connected with the live wire and the neutral wire respectively. Earthing is done with the thicker and longer one.

Question 23. Why do electrical appliances like electric bulb, heater, iron etc. work both with ac and dc?

Answer: The electrical appliances like electric bulb, heater, iron etc. work on the principle that heat is produced when electric current passes through a conductor. Heat produced in a conductor due to the flow of electric current depends on the resistance, amount of current and time of flow of current, which are independent of direction. Hence, produced heat does not depend on ac or dc.

Question 24. Why is the earth pin of a three-pin plug made longer and thicker?

Answer: The earth pin of a three-pin plug is made thicker so that this pin can not be inserted in the other two holes by mistake. Also, the earth pin is made longer so that the end of this pin gets connected with the socket before the other two pins and thereby reducing the chance of the user getting electric shock.

Question 25. Write down the construction of a socket in brief.

Answer:

Construction of a socket in brief

A socket is an important component of an electric circuit in which a plug is inserted. There are three holes in a socket. The lower two holes are connected with live wire and neutral wire whereas the upper, bigger hole is connected with earth wire. This socket is connected with the respective board.

Question 26. Why is the front portion of every pin of a three-pin plug split?

Answer: The front portion of every pin of a three-pin plug is split length-wise so that proper connection can be made with the socket. Without proper connection between the pin and the socket, sparks may fly due to loose connection which can be very dangerous.

 

 

 

Current Electricity Topic E Electromagnetic Induction And Domestic Electrical Circuit Very Short Answer Type Questions Choose The Correct Answer

 

Question 1. The colour of a live wire is

1. Brown
2. Black
3. Green
4. Sky blue

Answer: 1. Brown

Question 2. The colour of a neutral wire is

1. Brown
2. Black
3. Green
4. Skyblue

Answer: 2. Black

Question 3. Which of the following helps in the conversion of low voltage ac into high voltage ac?

1. Converter
2. Rectifier
3. Step-up transformer
4. Step-down transformer

Answer: 3. Step-up transformer

Question 5. Electromotive force (emf) is induced in a closed coil, when magnetic flux linked with the coil

1. Purely increases
2. Remains constant
3. Purely decreases
4. Either increases or decreases

Answer: 4. Either increases or decreases

Question 6. The direction of the induced emf in a circuit is determined by which law?

1. Lenz’s law
2. Faraday’s first law of electromagnetic induction
3. Faraday’s second law
4. Ampere’s swimming rule

Answer: 1. Lenz’s law

Question 7. No emf is induced in a closed coil when magnetic flux linked with the coil

1. Decreases
2. Is constant
3. Increases
4. Changes

Answer: 2. Is constant

Question 8. In electromagnetic induction, the induced emf in a coil is independent of

1. Change in the flux
2. Time
3. Resistance of the coil
4. All of these

Answer: 3. Resistance of the coil

Question 9. Lenz’s law is a consequence of the law of conservation of

1. Charge
2. Momentum
3. Energy
4. Mass

Answer: 3. Energy

Question 10. The instrument which converts mechanical energy into electrical energy is

1. Dynamo
2. Motor
3. Galvanometer
4. Barlow’s wheel

Answer: 1. Dynamo

Question 11. The basic principle in which dc generator works is

1. Magnetic effect of electricity
2. Electromagnetic induction
3. Chemical effect of electricity
4. Heating effect of electricity

Answer: 2. Electromagnetic induction

Question 13. In domestic circuit switch is connected in the

1. Live wire
2. Neutral wire
3. Earth wire
4. Fuse wire

Answer: 1. Live wire

Question 14. The thicker and longer pin of the three-pin plug is connected to

1. Live wire
2. Neutral wire
3. Live or neutral wire
4. Earth wire

Answer: 4. Earth wire

Question 15. The main fuse is connected in

1. Live wire
2. Neutral wire
3. Both the live and earth wire
4. Earth wire

Answer: 1. Live wire

 

Current Electricity Topic E Electromagnetic Induction And Domestic Electrical Circuit Answer In Brief

 

Question 1. When the north pole of a bar magnet is brought towards a closed coil along its axis, what is the direction of current in the front face of the coil?
Answer: The direction of current in the front face of the coil is anticlockwise.

Question 2. When the north pole of a bar magnet is taken away from a closed coil along its axis, what is the direction of current in the front face of the coil?
Answer: The direction of current in the front face of the coil is clockwise.

Question 3. When the south pole of a bar magnet is taken away from a closed coil along its axis, what is the direction of current in the front face of the coil?
Answer: The direction of current in the front face of the coil is anticlockwise.

Question 4. With the help of which instrument, alternating current (ac) of high voltage can be transformed into ac of low voltage and vice versa?
Answer: With the help of a transformer, alternating current (ac) of high voltage can be transformed into ac of low voltage and vice versa.

Question 5. In which direction does current pass through a live wire?
Answer: Current through a live wire passes from the direction of electricity supply station to the direction of electrical appliances.

Question 6. In which direction does current pass through a neutral wire?
Answer: Current through a neutral wire passes from the direction of electrical appliances to the direction of electricity supply station.

Question 7. What is the colour of live wire used in electric line in our homes?
Answer: The colour of live wire used in electric line in our homes is brown.

Question 8. What is the colour of neutral wire used in electri c line in our homes?
Answer: The colour of neutral wire used in electric line in our homes is sky blue.

Question 9. By means of which gadget, the electric line in our homes can be switched on and off?
Answer: With the help of the main switch, the electric line in our homes can be switched on and off.

Question 10. What is the colour of earthing wire?
Answer: The colour of earthing wire is either green or green with yellow stripe.

Question 11. Which wire is connected with the top big hole of a three pin plug?
Answer: Earthing wire is connected with the top big hole of a three pin plug.

Question 12. Which type of wire is generally used in house wiring?
Answer: Copper wire is generally used in house wiring.

Question 13. Which metal wire is generally used for the transmission of electricity to a distant place?
Answer: Aluminium wire is generally used for the transmission of electricity to a distant place.

Question 14. What is electromagnetic induction?
Answer: Electromagnetic induction is the phenomenon in which an emf is induced in a coil if there is a change in the magnetic flux linked with the coil.

 

Current Electricity Topic E Electromagnetic Induction And Domestic Electrical Circuit Fill In The Blanks

 

Question 1.If there is change of _____ linked with a closed coil, an emf is induced in the coil.
Answer: Magnetic Flux

Question 2. The cost of production generator is _____ than that of ac.
Answer: More

Question 3. When ac with high voltage is sent from a power station, loss of energy due to transmission of electricity is _____
Answer: Less

Question 4. When magnetic flux in a closed coil remains _____ no emf is induced in the coil
Answer: Stationary

Question 5. In ______ mechanical energy converted into electrical energy.
Answer: Generator

Question 6. Frequency of dc current is ______
Answer: Zero

Question 7. ac can be converted into dc by ______
Answer: Rectifier

Question 8. Lenz’s law actually follows the principle of conservation of _______
Answer: Energy

Question 9. In our domestic supply line frequency of ac is ______ Hz.
Answer: 50

Question 10. According to international convention, colour of the insulation of the neutral wire is ______
Answer: Blue

 

Current Electricity Topic E Electromagnetic Induction And Domestic Electrical Circuit State Whether True Or False

 

Question 1. Lenz’s law supports the law of conservation of energy.
Answer: True

Question 2. Induced emf is produced in a closed coil when it is placed in a magnetic field.
Answer: False

Question 3. If the north pole of a bar magnet moves towards a closed coil, the direction of induced current is anticlockwise in the front side of the coil.
Answer: False

Question 4. Magnitude of induced emf can be calculated from Faraday’s first law.
Answer: False

Question 5. In electroplating ac is used.
Answer: False

Question 6. Production cost of ac is less than that of dc.
Answer: True

Question 7. dc can be converted to ac by using converter.
Answer: True

Question 8. EMF produced by a generator is directly proportional to its number of turns
Answer: True

Question 9. Switches are connected in neutral wire.
Answer: False

Question 10. Fuse is always connected in the beginning of the circuit in live wire.
Answer: True

Question 11. According to colours of insulation are brown for live, light blue of neutral and green for earth
Answer: False

 

Current Electricity Miscellaneous Type Questions Match The Column

Question 1. 

Column A	Column B
Equivalent resistance in Ω	1. 48
Current flowing through the circuit in A	2. 3
Heat produced in the circuit for 2 seconds in J	3. 96
Power consumed in W	4. 4

 

Answer:

Equivalent resistance in Ω: 2. 3
Current flowing through the circuit in A: 4. 4
Heat produced in the circuit for 2 seconds in J: 3. 96
Power consumed in W: 1. 48

Question 2. 

Column A	Column B
6 x 108 esu of charge is equal to	1. 0.1 W • h
360 joule is equal to	2. 4 x 10-8  Ω • m
2.5 x 107 S • m-1 is equal to	3. 107 W
10 MW is equal to	4. 0.2 C

 

Answer:

6 x 10⁸ esu of charge is equal to: 4. 0.2 C
360 joule is equal to: 1. 0.1 W • h
2.5 x 10⁷ S • m^-1 is equal to:  2. 4 x 10^-8  Ω • m
10 MW is equal to: 3. 10⁷ W

WBBSE Solutions for Class 10 Physical Science and Environment

Chapter 2 Behaviour Of Gases Topic A Boyle’s Law And Charle’s Law Synopsis

WBBSE Class 10 Behaviour of Gases Overview

1. Pressure of a gas is defined as the normal force exerted by the gas molecules on the unit area of the wall of the container (in which the gas is kept).

2. Units of pressure in the CGS system and SI are Dyn/cm² and N/m², respectively. N/m² is also called Pa (pascal). 1 Pa = 10 Dyn/cm²

3. Dimensional formula of pressure is ML^–1T^-2.

4. The volume of a gaseous substance means the volume of the container in which it is kept.

5. Unit of volume in SI is m³ and in the CGS system is cm³. One practical unit of volume is liter (L).
1 m³ = 1000 L , 1L = 1000 cm³,
1 m³ = 106cm³

6. Dimensional formula of volume is L³.

Read and Learn Also WBBSE Solutions for Class 10 Physical Science and Environment

7. Manometer is used to measure the pressure of a gas or air. This is also called a pressure gauge.

8. The pressure exerted by a 76 cm long column of mercury at 0°C at sea level at the latitude of 45° is called the standard atmospheric pressure or normal atmospheric pressure (atm).

1 atm=1.013 x 10⁶ Dyn/cm²   Two other units of pressure is the bar and torr.
1 bar =10⁶ Dyn/cm² and 1 torr= pressure exerted by 1 mm long mercury column = 1332.8 Dyn/cm²

9. Boyle’s law: At constant temperature, the volume of a fixed mass of a gas is inversely proportional to the pressure of the gas. If a certain mass of a gas occupies a volume V at a pressure p at a constant temperature, then according to Boyle’s law, \(V \propto \frac{1}{p}\) or, pV=K, where K is a constant.

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∴ At a constant temperature, if  V₁, V₂, V_3……are volumes of a fixed mass of gas at pressure p₁,p₂, p₃ ….., respectively, then according to this law, p₁V₁=p₂V₂=p₃V₃=…. = constant.

10. Graphical representation of Boyle’s law:
(1)p-V graph: Plotting volume of a fixed mass of gas at a constant temperature, along) the horizontal axis and the corresponding pressure along the vertical axis, the obtained graph is a rectangular hyperbola.

(2)pV-p graph: Plotting p along the horizontal axis and corresponding pV along the vertical axis, the obtained graph is a straight line parallel to the p axis.

11. Charles’ law: At constant pressure, the volume of a given mass of a gas increases or decreases by  \(\frac{1}{273}\) the part of its volume at 0°C for every 1°C rise or fall in temperature.

Let, at constant pressure volume of a fixed mass of gas at 0°C is V_0.

According to Charles’ law, an increase in volume for 1°C rise in temperature= \( \frac{V_0}{273}\).

∴increase in volume for t°C rise in temperature=\(\frac{V_0 t}{273}\).

volume of the gas at t°C is V_t= \(V_0+\frac{V_0 t}{273}\) = \(V_0\left(1+\frac{t}{273}\right)\)

Similarly the volume of the gas at -t°C is  V_-t = \(V_0\left(1-\frac{t}{273}\right)\)

12. At constant pressure, the volume of a certain mass of gas becomes zero at -273°C. This temperature is called absolute zero. If measured accurately, the value of absolute zero temperature is -273.150C. This does not happen in reality because gas is converted into liquid much before it reaches this temperature and Charles’ law is not applicable to liquid.

13. Physicist Lord Kelvin introduced a new scale of measurement of temperature, whose zero point is taken as -273°C and the value of each degree is taken to be equal to one degree of Celsius scale. This scale is called the absolute scale or Kelvin scale of temperature.
If the temperature of a body is t°C on the Celsius scale and T K in the Kelvin scale, then T = t + 273.

14. Alternative form of Charles’ law: At constant pressure, the volume of a given mass of gas is directly proportional to its absolute temperature.

15. Charles’ law using absolute temperature: If a certain mass of a gas occupies a volume V at absolute temperature T at constant pressure, then according to Charles’ law,

V ∝ T or, V=KT, K = constant.

∴ if at a constant pressureV₁, V₂, V₃… be the volume of a fixed mass of gas at – temperature T₁K, T₂K, T₃K… respectively,
then, \(\frac{V_1}{T_1}=\frac{V_2}{T_2}=\frac{V_3}{T_3}\)=….= constant

16. Graphical representation of Charles’ law: For a certain mass of a gas at constant pressure, plotting temperature t (in°C) along the horizontal axis and volume V along the vertical axis, the graph obtained is a straight line, The straight line touches the horizontal axis at -273°C.

For a certain mass of a gas at constant pressure, plotting absolute temperature T (in K) along the horizontal axis and volume V along the vertical axis the graph obtained is a straight line passing through the origin.

Chapter 2 Behaviour Of Gases Topic A Boyle’s Law And Charle’s Law Short And Long Answer Type Questions

Understanding Gas Laws in Physics

Question 1. Explain the pressure of a gas on the pressure of the gas basis of molecular motion and the collision of gas molecules with the walls of the vessel.
Answer:

The pressure of a gas on the pressure of the gas basis of molecular motion and the collision of gas molecules with the walls of the vessel.

The force of attraction amongst the molecules of gaseous material is negligible. So the gas molecules are always moving randomly. The molecules always collide amongst themselves and also with the walls of the vessel and undergo a change of momentum.

The rate of change of momentum is force, i.e., the wall exerts force on the molecules. In reaction to the force exerted by the walls, gas molecules also exert force on the walls. This force per unit area acting perpendicularly on the wall of the vessel is the gas.

Wbbse Class 10 Physical Science Solutions

Question 2. Define the pressure of a gas. What are the units of pressure in the CGS system and SI? Establish a relationship between these two units.
Answer:

Pressure of a gas:

1. Pressure of a gas is the force per unit area exerted by the gas molecules on the walls of the vessel.

2. Units of pressure in CGS system and SI are Dyn/cm² and N/m², respectively.

3. The relation between the units is \(1 \mathrm{~N} / \mathrm{m}^2=\frac{10^5 \mathrm{dyn}}{10^4 \mathrm{~cm}^2}=10 \mathrm{dyn} / \mathrm{cm}^2\)

Question 3. What is the volume of the gas? What are the units of volume in CGS system and SI?
Answer:

The volume of the gas:

1. The volume of a gas is the volume of the container in which it is kept.
2. The units of volume in CGS system is cm³ or ml and in SI is m³.

Question 4. The height of the mercury column is h₁ in the open-end arm of the manometer U -tube and it is h₂ in the other arm of the U-tube. Compare the pressure of enclosed gas in the manometer with the atmospheric pressure: (1) when h₁>h₂, (2) when h₁<h₂, (3) when h₁= h₂.
Answer:

Given

The height of the mercury column is h₁ in the open-end arm of the manometer U -tube and it is h₂ in the other arm of the U-tube.

1. When h₁>h₂, it is understood that the pressure of the enclosed gas is more than the atmospheric pressure. If the pressure of the enclosed gas is p₁ and the atmospheric pressure of that place is p₀, then p₁ = p₀ + Pressure of a mercury column of height (h₁ – h₂)
∴p₁± = p₀ + (h₁ – h₂)dg where the density of mercury is d and acceleration due to gravity at that place is g.

2. If h₁<h₂, it is understood that the pressure of the enclosed gas is less than atmospheric pressure. If the pressure of the enclosed gas is p₂, then p₂= p₀ – (h₂ – h₁)dg.

3. If h₁ = h₂, it is understood that the pressure of the enclosed gas inside the manometer is equal to the atmospheric pressure. In this case, if the pressure of the enclosed gas is p₃, then p₃= p₀.

Question 5. By taking some amount of air on the top of the mercury column in a defective barometer, determine the pressure of the atmosphere.
Answer:

Let us assume, the height of mercury in this defective barometer is H₁ cm and the height of air column above the mercury column is x₁ cm. If the area of cross-section inside the tube is A cm², then the volume of air, V₁ = x₁ A cm³. If the atmospheric pressure is equal to the height of a mercury column of H cm, the pressure of this V₁ volume of air.

p₁ = pressure of (H — H₁) cm of mercury column. Now the open end of the barometer immersed in mercury is raised a little upward. If the height of mercury in the tube is H₂ and the height of air column above the mercury column is x₂ cm then the volume of enclosed air, V₂= x₂A cm³. Hence, the pressure of air, p₂= pressure of a mercury column of height (H – H₂)cm

Since the mass of enclosed air and temperature remain constant, we get from Boyle’s law,

p₁V₁=p₂V₂

or, (H- H₁).x₁A = (H-H₂). x₂A

or, Hx₁– H₁x₁ = Hx₂– H₂x₂

or, H(x₁-x₂) =H₁x₁ – H₂x₂

∴\(H=\frac{H_1 x_1-H_2 x_2}{x_1-x_2}\)

Boyle’s Law Explained with Examples

Question 6. Write down Boyle’s law and explain it. Or, State the law which establishes the relation p₁V₁=p₂V₂. Or, Write down the law from which the relation between the volume and the pressure of an ideal gas is known.

Answer:

1. Boyle’s law: At constant temperature, the volume of a fixed mass of a gas is inversely proportional to the pressure of the gas.

Explanation: If V and p are the volumes and the pressure of the gas respectively, then according to Boyle’s law

\(V \propto \frac{1}{p}\) (at constant temperature)
or \(V=\frac{K_1}{p}\) or, pV =K₁

where K₁ is a constant whose value depends on the mass and the temperature of the gas. Therefore, with the temperature of a fixed mass of gas remaining constant, the product of the pressure and the volume of the gas is constant. Now, if the temperature of a fixed mass of a gas remains constant and V₁, V₂, and V₃ are the volumes of the gas at pressures p₁, p_2, and p₃ respectively, then according to Boyle’s law,

Charles’s Law and Its Applications

Question 7. Write down Charles’ law and explain it.
Answer:

Charles’ law: At constant pressure, the volume of a given mass of a gas increases or decreases by \(\frac{1}{273}\) of its volume at 0°C for every 1°C rise or fall in temperature

Explanation: Let the volume of a given mass of a gas at constant pressure be V₀ at 0°C. By keeping the pressure constant, if the temperature of the gas is changed, then according to Charles’ law at 1°C the volume of the gas becomes

\(V_1=V_0+\frac{V_0}{273}=V_0\left(1+\frac{1}{273}\right)\)

At 2°C, the volume of the gas becomes

\(V_2=V_0+\frac{2 V_0}{273}=V_0\left(1+\frac{2}{173}\right)\)

In a similar way, at f°C the volume of the gas becomes

\(V_t=V_0\left(1+\frac{t}{273}\right)\)

Similarly, keeping the pressure constant, if the temperature is decreased by t°C, the volume of the gas becomes

\(V_t^{\prime}=V_0\left(1-\frac{t}{273}\right)\)

Question 8. Draw the graph of V-t of Charles’ law and give an idea of absolute zero temperature from it.
Answer:

At constant pressure, if a graph of a given mass of gas is drawn by taking a temperature (t) as abscissa and volume ( V) at that temperature as ordinate, then the curve obtained is a straight line.

If the straight line is extended backward, it cuts! the temperature axis at -273°C. This means that at constant pressure, the volume of a gas ’ becomes zero at -273°C. This temperature is called the absolute zero temperature.

Question 9. Write Charles’ law according to the absolute scale of temperature.
Answer:

Charles’ law according to the absolute scale of temperature:

If the volume of any gas of a given mass is V₀ at 0°C temperature, then according to Charles law, the volume of the gas at constant pressure and t₁°C becomes

Wbbse Class 10 Physical Science Solutions

\(V_1=V_0\left(1+\frac{t_1}{273}\right)\) or, \(V_1=V_0 \cdot \frac{273+t_1}{273}\) or, \(V_1=\frac{T_1}{273} V_0\) ……..(1)

where T1 is the reading of t1°C temperature in absolute scale. Similarly, volume of the same gas at constant pressure and t2°C becomes

\(V_2=V_0\left(1+\frac{t_2}{273}\right)\) or, \(V_2=V_0\left(\frac{273+t_2}{273}\right)\) or, \(V_2=\frac{T_2}{273} \cdot V_0\) ………(2)

where T2 is the reading of t2°C temperature in absolute scale. Now, adding equations (1) and (2), we get

\(\frac{V_1}{V_2}=\frac{T_1}{T_2}\) or, \(\frac{V_1}{T_1}=\frac{V_2}{T_2}\) or, \(\frac{V}{T}\) = constant
∴ V∞T

So, at constant pressure, the volume of a given mass of gas is directly proportional to the absolute temperature of the gas. This is an alternative form of Charles’ law.

Question 10. Why is the term ‘fixed mass of a gas’ mentioned while stating Boyle’s law?
Answer:

‘fixed mass of a gas’:

The term ‘fixed mass of gas is always mentioned at the time of stating Boyle’s law because the pressure and volume of the gas depend on mass. If the mass is changed, pressure and volume also get changed.

Question 11. Establish a relation between m³ and L
Answer:

Relation between m³ and L

1L = 10³ cm³
1m³ =10⁶ cm³= 10³• 10³cm³= 10³ L

Question 12. Draw the p-V curve according to Boyle’s law.
Answer:

p-V curve according to Boyle’s law:

At constant temperature, the volume (V) and the pressure (p) of a fixed mass of gas are plotted. Here, V/is plotted along the abscissa, and p is plotted along the ordinate. This is the p-V graph of Boyle’s law. The nature of the curve in the graph is a rectangular hyperbola.

Gay-Lussac’s Law in Everyday Life

Question 13. Draw the pV-p curve according to Boyle’s law.
Answer:

pV-p curve according to Boyle’s law:

we find a curve where the pressure p of a gas of fixed mass under constant temperature is plotted along the abscissa and the product (pV) of the pressure and the volume is plotted along the ordinate. This is the (pV-p) curve of Boyle’s law. Its nature is a straight line and it is parallel to the pressure axis.

Question 14. In the case of a real gas, how does the total volume of the molecules of the gas influence Boyle’s law?
Answer:

In the case of real gases, we cannot neglect the volume of the gas molecules and hence, pressure can be increased only up to a definite level at a certain temperature. For this reason, Boyle’s law cannot be accurately applied at any temperature.

Wbbse Class 10 Physical Science Solutions

Question 15. When a balloon is inflated, both its pressure and volume increase. Is Boyle’s law violated here?
Answer:

When the balloon is inflated, the mass of air inside the balloon does not remain constant. When air is pumped into the balloon, the mass of air inside it increases. We know that there are two constants in Boyle’s law—mass of the gas and its temperature. As the mass of air does not remain constant, so Boyle’s law is not applicable here. Hence, there is no question of its violation.

Question 16. Why does the volume of an air bubble increase when it goes up from deep inside a water body?
Answer:

Pressure of water increases as one goes deeper inside a water body. So, when air bubble comes upward from the depth of a water body, the pressure of water on it decreases gradually. Now suppose the temperature of water is uniform everywhere. Thus, according to Boyle’s law, when an air bubble comes upward from the depth, its volume is inversely proportional to the pressure of water, i.e., volume increases as pressure decreases.

Question 17. What is absolute scale of temperature?
Answer:

Absolute scale of temperature:

Physicist Lord Kelvin introduced a new scale for measurement of temperature whose zero point is taken as -273°C and the value of each degree is taken to be equal to one degree of Celsius scale. In SI, a temperature of 0.01°C is considered as 273.16 K in this scale. This scale is called the absolute scale of temperature.

Wbbse Class 10 Physical Science Solutions

Question 18.Calculate the value of absolute zero temperature from Charles’ law.
Answer:

If the volume of a given mass of gas at 0°C be V₀ , then according to Charles’ law, the volume of the gas at t°C and at constant pressure becomes

\(V_t=V_0\left(1+\frac{t}{273}\right)\)

Hence at -273°C, the volume of the gas becomes

\(V_{-273}=V_0\left(1+\frac{-273}{273}\right)=0\)

Therefore, according to Charles’ law, the volume of a gas becomes zero at -273°C and at constant pressure. This temperature is called ‘absolute zero temperature’.

Question 19. Draw the V’T graph of Charles’ law. Write the concept of absolute zero temperature from the graph.
Answer:

If a curve is drawn by taking the absolute temperature T of this gas as abscissa and the volume of the gas V on the ordinate, then this curve is a straight line. If the straight line is extended backward, it touches the origin. So, according to Charles’ law, the volume of a given mass of gas becomes zero at 0 K temperature, which is not possible in reality.

Question 20. Does the volume of gas become zero in reality at an absolute zero temperature?
Answer:

According to Charles’ law, the volume of any gas becomes zero at -273°C. But this does not occur in reality because long before reaching that temperature, the gas is converted into liquid and Charles’ law is not applicable to liquid.

Question 21. Calculate the value of absolute zero temperature in Fahrenheit scale
Answer:

Absolute zero temperature in Celcius scale (C) is at -273°C. Let us assume that the reading of absolute zero temperature in Fahrenheit scale is F.

Now from the eqaution, \(\frac{C}{5}=\frac{F-32}{9}\) ,

we get \(\frac{-273}{5}=\frac{F-32}{9}\)

∴F=-459.4°F

Question 22. The manufacturing company of a tube gives information regarding the pressure at which air has to be pumped in the tube of a rubber wheel of a car. But in reality, air is pumped in at a lower pressure. Why?
Answer:

Due to friction of the wheel with the road, rubber gets heated enormously. According to Charles’ law, air inside the tube increases in volume due to this. But the tyre does not increase in volume to that extent. So, air is pumped in at lower pressure so that there is no unnecessary extra pressure on the tube.

Chapter 2 Behaviour Of Gases Topic A Boyle’s Law And Charle’s Law Very Short Answer Type Questions Choose The Correct Answer

Question 1. The volume of a definite mass of gas at 0°C is V₀. What will be its volume if its temperature is raised to 100°C, keeping the pressure constant?

1. 293/273 V₀
2. 283/273 V₀
3. 303/273 V₀
4. 373/273 V₀

Answer: 4. 373/273 V₀

Question 2. In Boyle’s law,

1. Only mass of the gas remains constant
2. Only temperature of the gas remains constant
3. Mass and pressure of the gas remain constant
4. Mass and temperature of the gas remain constant

Answer: 4. Mass and temperature of the gas remain constant

Question 3. The volume (V) of a definite mass of an ideal gas is plotted against its temperature (f°C) at a constant pressure. What is the temperature at which the curve intersects the temperature axis?

1. 0°C
2. -136.5°C
3. -273°C
4. 273°C

Answer: 3. -273°C

Question 4. In which scale of temperature, it is not possible for the value of temperature to be negative?

1. Celsius scale
2. Fahrenheit scale
3. Absolute scale
4. All of these

Answer: 3. Absolute scale

Question 5. The pressure and volume of a definite mass of gas are given by p and V, respectively. If pressure is increased by 25% while keeping the temperature constant, what is the new volume?

1. 0.6V
2. 0.751V
3. 0.81V
4. 0.851V

Answer: 3. 0.81V

Question 6. 1 Pa = how many Dyn/cm²?

1. 1
2. 10
3. 100
4. 1000

Answer: 2. 10

Question 7. The nature of the p-V curve according to Boyle’s law Is

1. Straight line,
2. Circle
3. Parabola
4. Rectangular hyperbola

Answer: 4. Rectangular hyperbola

Wbbse Class 10 Physical Science Solutions

Question 8. The nature of pV-p curve according to Boyle’s law is

1. Straight line
2. Circle
3. Rectangular hyperbola
4. None of the above

Answer: 1. Straight line

Question 9. The value of absolute zero in the Fahrenheit scale is

1. -452.4°F
2. -462.4°F
3. -459.4°F
4. -463.4°F

Answer: 3. -459.4°F

Question 10. If force F acts perpendicular to the plane of a closed vessel of surface area A, then the pressure of the gas is

1. p = F-A
2. \(p=\frac{A}{F}\)
3. \(p=\frac{F}{A}\)
4. \(p=\sqrt{\frac{F}{A}}\)

Answer: 3. \(p=\frac{F}{A}\)

Question 11. Unit of pressure in SI is

1. N/m²
2. Bar
3. Torr
4. Dyn/cm²

Answer: 1. N/m²

Question 12. 1m³ = how many cm³ ?

1. 10³ 
2. 10⁴
3. 10⁵
4. 10⁶

Answer: 4. 10⁶

Question 13. 1m³ = how many L?

1. 1
2. 10
3. 100
4. 1000

Answer: 4. 1000

Question 14. The temperature of a fixed mass of gas is changed from 0°C to 30°C at constant pressure. What is the ratio of its initial and final volume?

1. 91:101
2. 91:100
3. 91:111
4. 91:121

Answer: 1. 91:101

Question 15. The temperature of a fixed mass changed from 0°C to 30°C by heating at constant pressure. How many times is the final volume of the initial volume?

1. 1.2 times
2. 1.5 times
3. 2 times
4. 3 times

Answer: 3. 2 times

Question 16. The volume of a definite mass of gas at room temperature and a pressure of 76 cm of mercury is 1 L. What is its volume at a pressure of 38 cm of mercury if the temperature remains constant?

1. 1.5L
2. 2L
3. 3L
4. 4L

Answer: 2. 2L

Wbbse Class 10 Physical Science Solutions

Question 17. At constant temperature, if the pressure on a definite mass of gas becomes 1/4 of its initial value then the volume increases by

1. 2 times
2. 3 times
3. 4 times
4. 5 times

Answer: 2. 3 times

Question 18. Two gases of equal mass are in thermal equilibrium. If p_a,p_b, and V_a, V_bare their respective pressure and volumes, which of the following relation is true?

1. \(p_a \neq p_b ; V_a=V_b\)
2. \(p_a=p_b ; V_a=V_b\)
3. \(\frac{p_a}{V_a}=\frac{p_b}{V_b}\)
4. \(p_a V_a=p_b V_b\)

Answer: 4. \(p_a V_a=p_b V_b\)

Question 19. An idle gas at 27°C is heated at constant pressure so as to triple its volume. The temperature of the gas will be

1. 600 K
2. 900°C
3. 627°C
4. 900°F

Answer: 3. 627°C

Chapter 2 Behaviour Of Gases Topic A Boyle’s Law And Charle’s Law Answer In Brief

Question 1. Which instrument is used to measure the pressure of air enclosed in a container?
Answer: Manometer is used to measure the pressure of air enclosed in a container.

Question 2. Pa (pascal) is a unit of which physical quantity?
Answer: Pa is the unit of pressure.

Question 3. What is the relationship between Pa and \(\frac{\mathrm{N}}{\mathrm{m}^2}\) ?
Answer: \(1 \mathrm{~Pa}=1 \mathrm{~N} / \mathrm{m}^2\)

Question 4. While measuring pressure of a gas in a closed container by a manometer, level of mercury is lower in the open-end arm than the other arm. What does it signify?
Answer: It signifies that pressure inside the closed container is lesser than the atmospheric pressure.

Question 5. While measuring pressure of a gas in a closed container with a manometer, level of mercury is lower in the open-end arm than the other arm. What does it signify?
Answer: It signifies that pressure inside the closed container is lesser than the atmospheric pressure

Question 6. Pressure of a gas depends on which factors?
Answer: The pressure of a gas depends on its mass, volume, and temperature.

Wbbse Class 10 Physical Science Solutions

Question 7. At constant pressure, the volume of a certain quantity of a gas depends on which factor?
Answer: The volume of a certain quantity of a gas at constant pressure depends on the temperature of the gas

Question 8. Mention the constants in Boyle’s law.
Answer:

Constants in Boyle’s law are:

1. Mass of gas and
2. Temperature

Question 9. Mention constants in Charles’ law.
Answer:

Constants in Charles’ law are:

1. Mass of gas and
2. Pressure of gas.

Question 10. What is the relationship between the Celsius scale and the absolute scale of temperature?
Answer: If the temperature of a body is t°C in the Celsius scale and T K in the absolute scale, then T=t+ 273.

Question 11. What is absolute temperature?
Answer:

Absolute temperature

Absolute temperature is the temperature of a body according to a scale where zero is taken as absolute zero.

Question 12. What is the value of freezing point of water in absolute scale?
Answer: Freezing point of water in absolute scale is 273 K.

Wb Class 10 Physical Science

Question 13. What is the boiling point of water in absolute scale?
Answer: The boiling point of water in absolute scale is 373 K.

Question 14. What is the nature of the V-t graph according to Charles’ law?
Answer: The V-t graph according to Charles’ law is a straight line intersecting the x-axis at -273 K.

Question 15. What is the nature of V-T graph according to Charles’ law?
Answer: The nature of the V-Tgraph according to Charles’ law is a straight line passing through the origin.

Question 16. At which temperature, the V-T curve of Charles’ law intersects the temperature axis?
Answer: The V-T curve of Charles’ law intersects the temperature axis at 0 K.

Question 17. Is it possible to have a temperature lower than the absolute temperature?
Answer: No, it is not possible to have a temperature lower than the absolute temperature.

Question 18. What would be the volume of an ideal gas at absolute zero temperature?
Answer: The volume of an ideal gas at absolute zero temperature is zero.

Question 19. What is the value of 400 K in Celsius scale?
Answer: The value of 400 K in Celsius scale = (400- 273)°C = 127°C

Wb Class 10 Physical Science

Question 20. If there is a 273 K change in temperature of a body, what is the corresponding value of this change in Celsius scale?
Answer: A change of 273 K in the temperature of the body results in a change of 273°C in Celsius scale.

Question 21. If the temperature of a body changes from 270 K to 273 K, what is its corresponding increase in Celsius scale?
Answer: Increase in temperature of the body = (273- 270)K = 3 K = 3°C (ncrease of temperature in Celsius scale).

Question 22. If the temperature of a body changes from 270 K to 273 K, what is the present temperature of the body in Celsius scale?
Answer: The present temperature of the body = 273 K =0°C.

Question 23. Does the absolute zero temperature of a gas depend on its nature, mass, volume or pressure?
Answer: No, absolute zero temperature of a gas does not depend on its nature, mass, volume or pressure.

Question 24. At low pressure or high pressure do the real gases roughly follow the equation PV=KT?
Answer: Real gases follow roughly the equation pV = KT at low pressure.

Chapter 2 Behaviour Of Gases Topic A Boyle’s Law And Charle’s Law Fill In The Blanks

Question 1. The volume of a gas increases if its temperature is increased or pressure is ______.
Answer: Decreased

Question 2. The volume of a gas decreases if its temperature is decreased or pressure is ______.
Answer: Increased.

Question 3. _________ developed an air pump to experimentally verify Boyle’s law.
Answer: Robert Hooke

Wb Class 10 Physical Science

Question 4. When air bubbles rise up from the bottom surface of deep water, the volume ______.
Answer: Increases

Question 5. If the volume of a fixed temperature is V₀, then its volume at t°C temperature and at constant pressure is _______.
Answer: V₀(1+t/273)

Question 6. In reality, we get _________  a temperature less than the absolute zero temperature.
Answer: Do not

Question 7. _______, a scientist introduced the concept of the absolute scale of temperature.
Answer: Kelvin

Question 8. Among solid, liquid, and gaseous materials, force of attraction between the molecules is highest in ________.
Answer: Solids

Question 9. _______  law is the law relating the pressure and volume of a gas of fixed mass at a constant temperature.
Answer: Boyle’s

Question 10. _______ law is the law relating the volume and temperature of a fixed mass of gas at constant pressure.
Answer: Charles’

Question 11. Due to a lack of experimental proof, the complete idea of atoms and molecules during Avogadro’s time was _______.
Answer: Hypothetical.

Wb Class 10 Physical Science

Question 12. If pressure of an enclosed air is more than the atmospheric pressure, the level of mercury in the open-end arm of a manometer is ______ than the other arm.
Answer: Higher

Question 13. If pressure of an enclosed air is less than the atmospheric pressure, the level of mercury in the open-end arm of a manometer is _______ than the other arm.
Answer: lower

Chapter 2 Behaviour Of Gases Topic A Boyle’s Law And Charle’s Law State Whether True Or False

Question 1. A pressure gauge is a device that is used to measure the pressure of the gas.
Answer: True

Question 2. According to Boyle’s law at a constant temperature, the volume of a given mass of gas is directly proportional to the pressure exerted by the gas.
Answer: True

Question 3. The volume of a certain mass of gas becomes zero at 0°C.
Answer: False

Question 4. A change of 1°C- is equal to 1 K on the Kelvin scale.
Answer: True

Question 5. Ideal gas does not obey Boyle’s law, Charles’ law, and equation of state.
Answer: True

Wb Class 10 Physical Science

Question 6. If V₁ and V₂ are the volumes of a fixed mass of gas at temperatures T₁ and T₂  respectively, then \(\frac{V_2}{V_1}=\frac{273+t_2}{273+t_1}\).
Answer: True

Question 7. A temperature of 0°C is considered as the lowest hypothetical value of temperature.
Answer: True

Question 8. The product of pressure and the volume of a fixed mass of gas at a fixed temperature remains constant.
Answer: True

Chapter 2 Behaviour Of Gases Topic A Boyle’s Law And Charle’s Law Numerical Examples Useful Relations

1. Mathematical expression of Boyle’s law: p₁V₁=p₂V₂ where, V₁ and V₂ are volumes of a fixed mass of a gas at pressures p₁ and p₂ at constant temperature.

2. Mathematical Expression of Charles’ law: \(V_t=V_0\left(1+\frac{t}{273}\right)\)

where V₀  is the volume of a fixed mass of a gas at temperature 0°C and Vt is the volume of the gas at t°C at constant pressure.

3. An alternative expression of Charles’ law ‘: \(\frac{V_1}{T_1}=\frac{V_2}{T_2}\)

where V₁ and V₂ are the volumes of a fixed mass of gas at constant pressure at a temperature T₁K, and T₂K respectively.

Avogadro’s Law and Molar Volume

Question 1. The volume and the pressure of a fixed mass of gas at constant temperature is 750 ml and 80 cm Hg, respectively. What should be the pressure of the gas at the same temperature to make the volume 1000 mL?

Answer: Initial pressure of the gas (p₁) = 80 cm Hg

Initial volume of the gas (V₁) = 750 mL

Final volume of the gas (V₂) = 1000 mL

Suppose, final pressure of the gas is p₂.

Since the temperature of the gas is constant, according to Boyle’s law,

p₁V₁=p₂V₂ or, \(p_2=\frac{p_1 V_1}{V_2}\)

∴  \(p_2=\frac{80 \times 750}{1000}=60 \mathrm{~cm} \mathrm{Hg}\)

Therefore, at the same temperature, the volume of the gas becomes 1000 mL at 60 cm Hg.

Question 2. The temperature of a gas of fixed mass is 27°C. At what degree Celsius temperature, the volume of this gas becomes double, if the pressure on the gas remains unchanged?
Answer: Initial temperature of the gas (T₁) = 27 + 273 = 300 K and initial volume (V₁)= V.

Suppose, volume is doubled at a temperature T₂ and V₂ = 2V.

As the pressure of the gas is constant, according to Charles’ law,

\(\frac{V_1}{V_2}=\frac{T_1}{T_2}\) or, \(V_1 T_2=V_2 T_1\) or, \(T_2=\frac{V_2 T_1}{V_1}\).

∴ \(T_2=\frac{2 V \times 300}{V}=600 \mathrm{~K}\)

Hence, final temperature of the gas in Celsius scale = (600 — 273) = 327°C

Wb Class 10 Physical Science

Question 3. Air is present inside a glass vessel at 67°C. Keeping its pressure unchanged, the temperature of the vessel is increased. At what temperature, of air will escape?
Answer: Initial temperature of air, T₁= 67 + 273 = 340 K

Suppose, initial volume = V₁ and  1/3 portion escapes at temperature T₂

If the final volume of air is V2, then

\(V_2=\left(1+\frac{1}{3}\right) V_1 \equiv \frac{4}{3} V_1\)

As the pressure remains constant, according to Charles’ law,

\(\frac{V_1}{T_1}=\frac{V_2}{T_2}\) or, \(V_1 T_2=V_2 T_1\) or,

\(V_1 T_2=\frac{4}{3} V_1 \times 340\) or, T₂=443.33K

Therefore, final temperature in Celsius scale = 453.33-273 = 180.33°C

Question 4. A balloon of volume 100 cm3 is taken at depth of 103.3 m inside a lake. What is its new volume? Atmospheric pressure is equal to the pressure of 10,33 m of water column.
Answer: Atmospheric pressure is equal to the pressure of a water column of 10.33 m. Volume (V₁) of balloon on the top surface of the lake = 100 cm³_.

Initial pressure (p₁) = p_a, where p_a is the atmospheric pressure.

Thus, pressure at the bottom of the lake, p₂ =p_a+ Pressure a 103.3 m water column

= \(p_1+\frac{103.3}{10.33}=11 p_a\)

Suppose, the volume of air in the balloon at the bottom of the lake = V₂

Now as the temperature is uniform throughout the lake, so according to Boyle’s law,

p₁V₁=p₂V₂

pa × 100

∴ \(V_2=\frac{p_1 V_1}{p_2}=\frac{p_a \times 100}{11 p_a}\)= 9.09 cm³

Hence, the volume at the bottom of the lake becomes 9.09 cm3.

Physical Science Class 10 West Bengal Board

Question 5. Some amount of air has been put into a barometer tube of length lm and as a result, its reading has come down from 76 cm to 70 cm. What is the volume of the air at standard atmospheric pressure? Standard atmospheric pressure = 76 cm Hg and the cross sectional area of the tube = 1 cm²
Answer: Cross-sectional area of the barometer tube (A) = 1 cm²
The reading of the barometer comes down from 76 cm to 70 cm when some amount of air is put inside it.

Thus, pressure of air in the barometer tube ( p₂) = 76 – 70 = 6 cm Hg and its volume (V₁) = (100 – 70) x 1 = 30 cm³

If the volume of the air is V₂ at standard atmospheric pressure or p₂ = 76cm Hg, then according to Boyle’s law,

p₁V₁=p₂V₂ or, \(V_2=\frac{p_1 V_1}{p_2}\)

∴ V₂= \(\frac{6 \times 30}{76}\) =  2.368 cm³

Question 6. The volume of a gas is 3 L at 27°C. By keeping the pressure constant, if the temperature is increased to 127 °C, its volume becomes 4 L. Calculate the value of absolute zero temperature.
Answer: Suppose, absolute zero temperature = T₀ °C

Therefore, initial temperature (T₁) of the gas = (27 – T₀) K and its volume (V₁) = 3 L and final temperature (T₂) = (127 – T₀) K and its volume (V₂) = 4L

As the pressure is constant, so according to Charles’ law,

\(\frac{V_1}{T_1}=\frac{V_2}{T_2}\) or, \(\frac{3}{27-T_0}=\frac{4}{127-T_0}\)

Question 7. At 95 cm of Hg pressure a balloon is filled with 0.8 L air. Find the volume of the balloon if pressure is decreased to 76 cm of Hg keeping the temperature constant.
Answer: According to the question, initial pressure (p₁) = 95 cm of Hg, initial volume (V₁) = 0.8 L, and final pressure (p₂ ) = 76 cm of Hg.
Suppose the final volume of the balloon is V₂ L.
As temperature and mass of the air inside the balloon are constant, according to Boyle’s law,
p₁V₁=p₂V₂ or, \(V_2=\frac{p_1 V_1}{p_2}\)

∴  \(V_2=\frac{95 \times 0.8}{76}=1.0\)

Ideal Gas Law: Formula and Applications

Question 8. Two vessels of volume V and V’ contain air at the same temperature and their pressures are p₁ and p₂  respectively. They are joined by a tube of negligible volume. Find the final pressure of the system (at equilibrium).
Answer: Total volume of the system V=V’ +V” Final pressure of the system (p) = pressure due to the fist gas for the entire volume V + pressure due to the second gas for the entire volume V
∴ P=p’₁+p’₂

As the temperature is constant, according to Boyle’s law.
p’₁V= p₁V’   or,  \( p_1^{\prime}=\frac{p_1 V^{\prime}}{V}\)
and p’₂V= p₂V”  or, \(p_2^{\prime}=\frac{p_2 V^{\prime \prime}}{V}\)
∴ \(p=p_1^{\prime}+p_2^{\prime}=\frac{p_1 V^{\prime}}{V}+\frac{p_2 V^{\prime \prime}}{V}\)
= \(\frac{p_1^{\prime} V^{\prime}+p_2^{\prime} V^{\prime \prime}}{V}\)
= \(\frac{\dot{p}_1^{\prime} V^{\prime}+p_2^{\prime} V^{\prime \prime}}{V^{\prime}+V^{\prime \prime}}\)

Chapter 2 Behaviour Of Gases Topic B Combination Of Boyle’s Law And Charles’ Law, Ideal Gas Equation, Avogadro’s Law Synopsis

1. Combined form of Boyle’s law and Charles’ law: If the volume and pressure of a given mass of gas at absolute temperature T are V and p respectively, then the combined form of Boyle’s law and Charles’ law is
\(V \propto \frac{T}{p}\) or, \(V=\frac{K T}{p}\) or, pV=KT or, \(\frac{p V}{T}=K\)
where K is a constant,-whose value depends on the mass of the gas and also on units of volume, temperature, and pressure.

2. Avogadro’s law: At same temperature and pressure, equal volumes of all gases contain the same number of molecules. Volume in Avogadro’s law refers to the volume of the space occupied by the gas and not the volume of the molecules present inside the gas.

3. Gay-Lussac’s Law: When gasses combine to form gaseous chemical compounds or compounds, the volumes of the reacting gases and that of the product (or those of the products) are in the ratio of small whole numbers, measured under the same conditions of pressure and temperature.

4. Avogadro number: Number of molecules present in 1 mole of substances. It is denoted by n_A and n_A = 6.022 X 10²³

5. Mathematical form of Avogadro’s law: If at a particular temperature and pressure, n moles of a gas occupies volume V, then according to Avogadro’s law,
V ∞ n or, V = kn, k = constant or, V/n = constant or,  \(\frac{V_1}{n_1}=\frac{V_2}{n_2}\)

6. Combination of Boyle’s law, Charles’ law, and Avogadro’s law: Let, at temperature T K and pressure p, n moles of a gas occupies volume V.
Now, according to Boyle’s law, \(\vee \propto \frac{1}{p}\) when n, T are constant.
According to Charles’ law, V ∝ T, when n and p are constant.
According to Avogadro’s law, V ∝ {where  n, when p and T are constant.
From the above relations, we get,
[layex]V \propto \frac{n T}{p}[/latex], when p, T and n all vary.
or, \(V=\frac{R n T}{p}\) R is a constant or, pV = nRT
This equation is known as the ideal gas equation for n-gram moles of an ideal gas.

7. R is called the molar gas constant or universal gas constant. The value of R is independent of the nature of the gas.
8. Units and value of R: In the CGS system, R = 8.314 x 10⁷ erg • mol^-1 • K^-1 in SI, R = 8.314 J • mol^-1 • K^-1
9. Dimensional formula of R: dimensional formula of R is \(M L^2 T^{-2} N^{-1} \Theta^{-1}\) [dimension of temperature =Θ and amount of substance (mole) =N]

10. Ideal gas and real gas: A gas that obeys equation of state pV = nRT under all conditions is called an ideal gas. The gases which does not obey Boyle’s law or Charles’ law or Avogadro’s law or equation of state pV = nRT are called an ideal gases. But in reality, no known gas obeys the equation pV = KT except at high temperature and low pressure, hence they are called real gas.

Physical Science Class 10 West Bengal Board

11. Basic assumptions of the kinetic theory of gases:

(1)Gases are composed of a large numbers of molecules. For a particular gas the molecules are identical but they are different for different gases.
(2)Gas molecules are assumed as point masses, sum of their volumes is negligible compared to the volume of the container.
(3)Within the container the molecules are in ceaseless, random motion in all possible directions. .
(4)During motion, the molecules collide with each other and with the walls of the container. There collisions are perfectly elastic i.e., no loss in energy during collision.
(5)There is no force of attraction or repulsion between the gas molecules. Hence the potential energy of a gas molecule is zero, the total energy is its kinetic energy.
(6)The value of molecular velocities varies from zero to infinity.
(7)If temperature of the container remain unchanged, number of molecules of unit volume anywhere inside the container is always same.

12. Reasons of deviation from ideal behavior:

1. Ideal gas molecules are point masses. But real gas molecules have finite volumes.
2. There is no force of attraction or repulsion between ideal gas molecules. But weak intermoiecular force acts between real gas molecules.

Chapter 2 Behaviour Of Gases Topic B Combination Of Boyle’s Law And Charles’ Law, Ideal Gas Equation, Avogadro’s Law Short And Long Answer Type Questions

Question 1. Establish the combined form of Boyle’s and Charles’ law.
Answer:

The combined form of Boyle’s and Charles’ law

Suppose, pressure and volume of a fixed mass of any gas at absolute temperature T are p and V, respectively.

According to Boyle’s law, \(V \propto \frac{1}{p}\) (when mass of gas p and T are fixed).

According to Charles’ law, V ∞ T (when mass of gas and p are fixed).

Thus, according to the law of combined variation, \(V \propto \frac{T}{p}\) (when mass of a gas is fixed but both T  and p are variables)

or V=KT/P or, pV=KT

∴ \(\frac{p V}{T}=K\) ……..(1) where K is a proportional constant.

Let the initial pressure, volume and absolute temperature of a fixed mass of gas be p_1, V₁, T₁, and the final pressure, volume, and absolute temperature be p₂, V_2, and T₂ respectively. Then from equation (1), we get

\(\frac{p_1 V_1}{T_1}=K\) and \(\frac{p_2 V_2}{T_2}=K\)

∴ \(\frac{p_1 V_1}{T_1}=\frac{p_2 V_2}{T_2}\)

This is the combined form of Boyle’s law and Charles’ law.

Question 2. Under what circumstances, a real gas may behave like an ideal gas? Or, Give the arguments in favour of considering a real gas as an Ideal gas.
Answer: The volume of a definite mass of a real gas increases steadily when the pressure on it is reduced under constant temperature. Again, the volume of a definite mass of a real gas increases steadily when the temperature of it is increased under constant pressure. As the volume of the gas increases, the mutual distance between its molecules also increases.

As a result, the value of mutual attractive force between the molecules is also reduced. For an ideal gas, it is assumed that there is no mutual attractive force between the molecules. With these arguments, a real gas behaves like an ideal gas under the lowest possible pressure or the highest possible temperature.

Physical Science Class 10 West Bengal Board

Question 3. What are the contributions of Avogadro’s hypothesis?
Answer:

Contributions of Avogadro’s hypothesis:

1. Atoms and molecules are differentiated for the first time, in Avogadro’s hypothesis.
2. Gay- Lussac’s law of gaseous volume can be explained satisfactorily with the help of Avogadro’s hypothesis.
3. With this hypothesis correlation can be established between Dalton’s atomic theory and Gay-Lussac’s law of gaseous volume.

Question 4. The molar volumes of real gases at any given temperature and pressure are more or less equal and its limiting value at STP is 22.4 L • mol^-1. From the above experimental facts, deduce Avogadro’s hypothesis.
Answer:

The molar volumes of real gases at any given temperature and pressure are more or less equal and its limiting value at STP is 22.4 L • mol^-1.

The value of molar volume does not depend on the nature of the gaseous material. If the temperature and the pressure remain constant, then the values of molar volumes of different real gases remain nearly equal. If the volume of nmol of gas is V, then the molar volume becomes \(\frac{V}{n}\).

As the volume of a gas changes due to change” in its temperature and pressure, so the molar volume also changes due to change of temperature and pressure. It has been experimentally proved that at standard temperature and pressure, i.e., at STP, the value of the molar volume of any gaseous material is more or less the same and its limiting value is 22.4 L or 22400 mL.

This volume is called the molar volume of a gas at STP. So, at STP, 22.4 liters of every gas contain an equal number of molecules. From this experimental result, scientist Avogadro postulated his famous theory regarding the volume and molecules of any gaseous material. This theory is known as Avogadro’s hypothesis.

Question 5. Explain how Avogadro’s law combines Gay-Lussac’s law and Dalton’s atomic theory.
Answer: It is known that hydrogen chloride (HCI) gas is formed when hydrogen (H) gas and chlorine (Cl) gas react with each other. The reaction is given by H₂ + CI₂ = 2HCI.

According to Gay-Lussacs’s law of gaseous volume, 1 unit volume of H has to react with 1 unit volume of Cl to produce 2 units volume of HCI.

Now, according to Avogadro’s hypothesis, 1 elementary particle of H +1 elementary particle of Cl = 2 elementary particles of HCI Meanwhile according to Dalton’s atomic theory, the smallest elementary particle of matter is atom which is indivisible.

Therefore for hydrogen or chlorine, the elementary particle is molecule rather than an atom. Atoms and molecules were first differentiated while explaining Gay-Lussac’s gaseous volume from Avogadro’s hypothesis. Hence, Avogadro’s law combined Dalton’s atomic theory and Gay-Lussac’s law of gaseous volume

Wbbse Class 10 Physical Science Chapter 6 Question Answer

Question 6. Show that wet air is lighter than dry air by using the molar masses of water, nitrogen, and oxygen. Or, Give the reason for air to be lighter in rainy season than in winter.
Answer: We know, \(\text { density }=\frac{\text { mass }}{\text { volume }}\). By any means, if P volume the amount of water vapor increases in air, the mass of air decreases, and as a result, the density of air decreases. The amount of nitrogen and oxygen is high in dry air.

Molar mass of nitrogen is 28 g and the molar mass of oxygen is 32 g. Again, molar mass of water (H₂0) = 1×2 + 16 = 18 g
Now, suppose, some amount of dry air is taken in a closed vessel. Then, by keeping temperature and volume unchanged, 4 molecules of N₂ and 1 molecule of O₂ are taken out of the vessel and 5 molecules of H₂0 are introduced.

In this case, mass (M₁) of (4 molecules of N₂ + 1 molecule of O₂).
=\(\left(\frac{4 \times 28}{N_A}+\frac{1 \times 32}{N_A}\right)=\frac{144}{N_A} g\)

But mass of 5 molecules of H₂0
M₂= \(\frac{5 \times 18}{N_{\mathrm{A}}}=\frac{90}{N_{\mathrm{A}}} \mathrm{g}\)

Hence, M₂<M₁. Clearly, total mass of wet air inside the vessel is also reduced in this process. As a result, the density of wet air inside the vessel is also reduced. Thus, the wet air of the rainy season is lighter than dry air of winter

Question 7. Establish the ideal gas equation formed by combining Boyle’s law, Charles’ law, and Avogadro’s hypothesis.
Answer: According to Boyle’s law, \(V \propto \frac{1}{p}\) [when T and n are constant] ……..(1)

According to Charles’ law, V∝T [when p and n are constant]……(2)
According to Avogadro’s hypothesis, V∝n [when p and T are constant]…(3)

where, p = pressure of gas, V = volume of gas, T = temperature (in kelvin), n = number of moles. By combined variation, we get from equations (1],(2),(3).

 

\(V \propto \frac{n T}{p}\) [where p and T are variables.
or, \(V=\frac{n R T}{p}\) or, pV = nRT

Where R is the molar gas constant or universal gas constant. This equation is the ideal gas For n mole of gas.

Wbbse Class 10 Physical Science Chapter 6 Question Answer

Question 8. Calculate the unit of R by the dimensional analysis of ideal gas equation.
Answer:

We get \(R=\frac{p V}{n T}\) from the ideal gas equation, pV = nRT for n mol of gases.

∴ dimensional formula of R.

= dimensional formula of pressure X dimensional formula of volume/ dimensional formula of mole number X dimensional formula of temperature
= dimensional formula of force /(dimensional formula of length)² X (dimensional formula of length)³ / dimensional formula of mole number X  dimensional formula of temperature
= dimensional formula of work/ dimensional formula of mole number X dimensional formula of temperature

So, unit of universal gas constant \(R=\frac{\text { unit of work }}{\text { unit of mole number } \times \text { unit of temperature }}\)

Therefore, unit of R in SI is j • mol^-1 • K^-1 and unit of R in CGS system is erg •mol^-1 • K^-1. Here, the temperature is absolute temperature. So, its unit is expressed in K (kelvin).

Question 9. Calculate the value of universal of constant R.
Answer:

Ideal gas equation for 1 mol of any gas at STP is p₀V₀ = RT₀
where p₀ = standard pressure, T₀ = standard temperature = 273 K and V₀ = volume of,1 mole of gas at STP = 22400 cm³
∴p₀ = pressure of 76 cm of mercury column = 76 x 13.6 X 980 Dyn/cm² 
Now, we get R=\frac{p_0 V_0}{T_0}= from p₀V₀ = RT₀ gas or, \(R=\frac{76 \times 13.6 \times 980 \times 22400}{273}\)
∴ R = 8.31 X 10⁷ erg mol^-1 • K^-1 = 8.31 J. mol^-1 K^-1

Question 10. Write down the basic assumptions of kinetic theory of an ideal gas.
Answer: The basic assumptions of the kinetic theory of an ideal gas are as follows:
1. All the gases are composed of many molecules. Molecules of the same gas are of same nature but molecules of different gases are of different nature.

2. Gas molecules behave like point masses. So, volume of the molecules is negligible compared to the volume of the vessel.

3. Until the molecules collide amongst themselves and with the walls of the vessel, they move in straight lines with uniform speed. As a result of the collision, the motion of the molecules become disorderly.

4. The total linear momentum and the total kinetic energy of the molecules before and after the coliision remain unchanged.

5. No attractive or repulsive force acts within the gas molecules, i.e., there is no potential energy of the molecules and the entire energy is kinetic energy.

Wbbse Class 10 Physical Science Chapter 6 Question Answer

Question 11. Give two arguments in favour of the mobility of gas molecules.
Answer:
1. Pressure and diffusion are the two properties of gases which prove that the gas molecules are mobile. Gas molecules always collide amongst themselves and also with the walls of the vessel.

2. A force is exerted on the wall when the molecules collide against it. Pressure of a gas is equal to this force per unit area acting perpendicular to the wall of the vessel.
Further, two or more gases mix amongst themselves on their own. This is called diffusion. Therefore, both pressure of a gas and diffusion arise due to movement of the gas molecules.

Question 12. Discuss the influence of pressure on the volume of a gas.
Answer:
1. If the pressure on an enclosed gas is increased, distance between the molecules decreases. As a result, volume of the gas decreases. Due to decrease in the volume, number of collisions per second on unit area of the wall increases.

2. As a result, pressure of the gas increases and the external pressure and the internal pressure become equal and act in opposite directions.

3. In the same way, if the external pressure is decreased, distances between the molecules increase and as a result, volume increases. Due to increase of the volume, number of collisions per second on unit area of the wall decreases and consequently, the pressure of the gas decreases.

4. Here also, the external pressure and the internal pressure become equal and act in opposite directions.

Question 13. What is diffusion? Which properties of the gas molecules are known due to diffusion? Or, If an incense stick is ignited inside the room, the fragrance of the stick spreads within the room in a very short time. This phenomenon takes place due to which property of the gas? Write down the reasons.
Answer:
1. Diffusion is the phenomenon by which two or more non-reacting gases (light or heavy) are mixed spontaneously to form a homogeneous mixture, when they come in contact with each other.

2. If an incense stick is ignited inside a room, the fragrance of the stick spreads within the room in a very short time. As soon as the stick is ignited, there is collision among the gas molecules and also with the molecules of the air. Due to frequent collisions, the direction of motion of the gas molecules gets changed every moment.

3. The intermolecular space is much more than the volume of the gas molecules. As a result, the motion of the molecules of a particular gas enables them to enter into another gas through that intermolecular space and spread within a short time.

4. So, it is known through the process of diffusion that gas molecules are in motion and their motion is disorderly.

Wbbse Class 10 Physical Science Chapter 6 Question Answer

Question 14. Why the volume of a real gas of a definite mass at constant temperature and high pressure does not decrease in accordance with Boyle’s law, even if the pressure on it is increased? Or, Boyle’s law is applicable for an ideal gas but not for a real gas at high pressure. Why?
Answer:

1. According to the conditions of kinetic theory of gases, total volume of the molecules of a gas is negligible compared to the volume occupied by the gas.

2. But molecules of a real gas, though small, have a finite volume. If pressure is increased, the above mentioned condition remains valid upto a pressure of 1 atmosphere, but at higher pressure the molecules of the gas come very near to each other.

3. As a result, when the pressure is increased on the real gases already kept at high pressure, their volumes do not decrease likewise according to Boyle’s law.

Question 15. How is the presence of intermolecular forces responsible for deviation of a real gas from an ideal gas?
Answer: The pressure of a real gas is less than that of an ideal gas at same temperature and for same mass and volume. This is a deviation of an ideal gas from a real mass.

Explanation: When a gas molecule remains inside the vessel and is slightly away from the wall of the vessel, then it experiences an equal attractive force by the molecules all around it from every direction. As a result, resultant force on that molecule becomes zero. But when a molecule is very near the wall of the vessel, then the molecules inside the vessel and away from the wall exert an inward resultant force on that molecule.

As a result, the velocity of the molecule is reduced and thus strikes the wall at a lower speed. Now according to the kinetic theory of an ideal gas, there are no intermolecular forces between the molecules. So, real gas exerts comparatively less amount of pressure on the wall due to the presence of intermolecular forces.

Question 16. Mention two observations which prove the presence of mutual attractive forces between the gas molecules.
Answer: The following two observations prove the presence of intermolecular forces in a real gas:
1. Any gas gets condensed into liquid at a definite temperature when its temperature is reduced. Explanation: When temperature is reduced, kinetic energy of the gas molecules is also reduced. As a result, the molecules come nearer to each other only due to mutual attractive force. More the molecules come nearer to each other, more the value of intermolecular force increases. Hence, the gas gets condensed into liquid.

2. The pressure of a real gas is slightly less than the pressure of an ideal gas under similar conditions.

Explanation: When a molecule comes very near to the wall of a closed vessel, then that molecule exerts comparatively less force on the wall. This is due to the fact that the molecule which has come closer to the wall of the vessel is attracted by the other molecules away from the wall. So, pressure of the gas is slightly less than the pressure of an ideal gas under similar conditions.

Question 17. Determine the dimensional formula for universal gas constant.
Answer: The ideal gas equation for n mol of gases is pV = nRT; where p = pressure, V = volume, T = absolute temperature and R is the universal gas constant.

∴\(R=\frac{p V}{n T}\)

Hence, the dimensional formula of R = =\(\frac{M L^{-1} T^{-2} \times L^3}{N \times \Theta}=M L^2 T^{-2} N^{-1} \Theta^{-1}\)

Wbbse Class 10 Physical Science Chapter 6 Question Answer

Chapter 2 Behaviour Of Gases Topic B Combination Of Boyle’s Law And Charles’ Law, Ideal Gas Equation, Avogadro’s Law Very Short Answer Type Question Choose The Correct Answer

Question 1. Real gases behave like ideal gas at

1. High pressure and low temperature
2. Low pressure and high temperature
3. Low pressure and low temperature
4. High pressure and high temperature

Answer: 2. Low pressure and high temperature

Question 2. Molar mass of water is

1. 16g
2. 18g
3. 20g
4. 22g

Answer: 2. 18g

Question 3. Mass of 5 mol hydrogen gas is

1. 5g
2. 10g
3. 20g
4. 15g

Answer: 2. 10g

Question 4. During the collision of molecules of an ideal gas

1. Only linear momentum remains conserved
2. Only kinetic energy remains conserved
3. Both linear momentum and kinetic energy remain conserved
4. Neither linear momentum nor kinetic energy remains conserved

Answer: 3. Both linear momentum and kinetic energy remain conserved

Question 5. The energy of the molecules of an ideal gas is

1. Only potential energy
2. Only kinetic energy
3. The sum of potential energy and kinetic energy
4. The difference of kinetic energy and potential energy

Answer: 2. Only kinetic energy

Question 6. Which quantity is a constant in the equation pV = nRT?

1. p
2. V
3. T
4. R

Answer: 4. R

Question 7. Value of the universal gas constant in the CGS system is

1. 8.31 × 10⁶ erg. mol^-1 K^-1
2. 8.31 × 10⁷ erg . mol^-1 K^-1
3. 8.31 × 10⁸ erg . mol^-1 K^-1
4. 8.31 × 10⁹ erg . mol^-1 K^-1

Answer: 2. 8.31 × 10⁷ erg . mol^-1 K^-1

Question 8. If x number of molecules are present in volume V of He gas at pressure p and temperature T, then the number of molecules present in a volume 3 V of O₂ gas at the same pressure and temperature is

1. x
2. 3x
3. x/3
4. 9x

Answer: 2. 3x

Question 9. The freezing point of water in an absolute scale is

1. 0 K
2. 273 K
3. 373 K
4. 173 K

Answer: 2. 273 K

Question 10. The dimensional formula of universal gas constant is

1. \(\mathrm{ML}^2 \mathrm{TN}^{-1} \Theta^{-1}\)
2. \(M L^2 T^{-2} N^{-1} \Theta^{-1}\)
3. \(M L^2 T^{-2} N^{-1} \Theta\)
4. \(M L^2 T^{-1} N^{-1} \Theta^{-1}\)

Answer: 3. \(M L^2 T^{-2} N^{-1} \Theta\)

Question 11. According to the kinetic theory of gases, at what temperature the molecule of an ideal gas has zero kinetic energy?

1. 273 K
2. 300 K
3. 0 K
4. 100 K

Answer: 3. 0 K

Wbbse Class 10 Physical Science Chapter 6 Question Answer

Question 12. 84g N₂ = how many moles?

1. 1
2. 2
3. 3
4. 4

Answer: 3. 3

Question 13. Among 2g H₂, 28g N_2, and 44 g CO₂, which one has the largest volume at STP?

1. 2gH₂
2. 28gN₂
3. 44gCO₂
4. All have the same volume

Answer:  4. All have the same volume

Question 14. If Avogadro number is N, then one mol of C02 contains how many molecules?

1. N
2. 2N
3. 3N
4. 4N

Answer: 3. 3N

Question 15. The mass of one molecule of oxygen is

1. 5.31 × 10^-23g
2. 10.62 × 10-23g
3. 15.93 × 10-23g
4. 2.65 × 10-23g

Answer: 1. 5.31 × 10^-23g

Question 16. What is the molecular mass of CO₂ when the mass of 11.2 L of CO₂ at STP is 22g?

1. 22
2. 44
3. 88
4. 11

Answer: 2. 44

Question 17. The number of molecules present in 7g of N₂ gas is

1. 12.044 × 10²³
   
2. 1.506 × 10²³
   
3. 3.011 × 10²³
   
4. 6.022 × 10²³

Answer: 2. 1.506 × 10²³

Question 18. The amount of work done by expansion of 1 mol ideal gas against fixed pressure when its temperature is increased by 1K is

1. R
2. 2 R
3. 3 R
4. 4 R

Answer: 1. R

Wbbse Class 10 Physical Science Chapter 6 Question Answer

Question 19. The volume of 2.2 g of CO₂ at 27°C and a pressure of 570 mm of the mercury column is

1. 4.92 L
2. 0.82 L
3. 3.28 L
4. 1.64 L

Answer: 4. 1.64 L

Question 20. The behavior of real gases show maximum deviation from the behavior of ideal gas under

1. Low pressure and low temperature
2. Low pressure and high temperature
3. High pressure and low temperature
4. High pressure and high temperature

Answer: 3. High pressure and low temperature

Question 21. There is N number of molecules in nmol of a gas. Value of – is n

1. 9.033 x 10²³
2. 12.044 x 10²³
3. 3.011 x 10²³
4. 6.022 x 10²³

Answer: 4. 6.022 x 10²³

Question 22. The equation of state of 7 g of oxygen is

1. pV=7RT
2. \(p V=\frac{32}{7} R T\)
3. \(p V=\frac{7}{32} R T\)
4. pV= 14RT

Answer: 4. pV= 14RT

Question 23. What is the value of pV for 1.12 L for an ideal gas at STP?

1. 2RT
2. RT
3. 0.05RT
4. 1.12RT

Answer: 3. 0.05RT

Question 24. No of moles present per unit volume (L) of an ideal gas is

1. pRT
2. \(\frac{p}{R T}\)
3. \(\frac{R T}{p}\)
4. \(\frac{p T}{R}\)

Answer: 2. \(\frac{p}{R T}\)

Chapter 2 Behaviour Of Gases Topic B Combination Of Boyle’s Law And Charles’ Law, Ideal Gas Equation, Avogadro’s Law Answer In Brief

Question 1. At low temperature or high temperature do the real gases roughly follow the equation pV=KT?
Answer: Real gases roughly follow the equation pV = KT at high temperature.

Question 2. How is the pressure of a definite mass of gas related to the motion of its molecules?
Answer: Keeping the volume of a definite mass of gas constant, if the velocity of the molecules of the gas increases, pressure of the gas inside the vessel also increases.

Question 3. What is molar volume?
Answer:

Molar volume

The volume occupied by one gram mole of any gaseous substance (elementary or compound) at a fixed temperature and pressure is called the gram molar volume or molar volume.

Question 4. Does the value of molar volume depend on the nature of the gas?
Answer: No, the value of molar volume does not depend on the nature of the gas.

Question 5. The value of molar volume depends on which factor?
Answer: The value of molar volume depends on the pressure and temperature of the gas.

Question 6. What is the limiting value of molar volume of any real gas at STP?
Answer: The limiting value of molar volume of any gaseous material at STP is 22.4 L or 22400 mL.

Question 7. What is meant by the volume of a gas in Avogadro’s hypothesis?
Answer: Volume of a gas in Avogadro’s hypothesis means the volume of the space occupied by the gas.

Question 8. Who is the first scientist to differentiate between atoms and molecules?
Answer: Avogadro is the first scientist to differentiate between atoms and molecules.

Question 9. How to reduce the density of air of a place at a definite temperature?
Answer: If the amount of water vapour at a place at a definite temperature increases due to some reason, density of air gets reduced.

Question 10. The number of molecules in a balloon filled with hydrogen gas is N. What is the number of molecules in a balloon filled with an equal volume of nitrogen at the same temperature and pressure?
Answer: The number of molecules in a balloon containing equal volume of nitrogen gas at the same temperature and pressure is also N.

Question 11. Between dry air and wet air, which one has less density?
Answer: Wet air has less density than dry air.

Question 12. Is there any change in the kinetic energy of the gas molecules in a perfectly elastic collision?
Answer: In a perfectly elastic collision, kinetic energy of the gas molecules remains conserved.

Question 13. The fragrant fumes of a burning incense stick placed at one corner of the room are perceived by smell at another corner of the room. Which property of the gas molecules is demonstrated by this?
Answer: The property of motion of gas molecules is demonstrated by this.

Question 14. The fragrant fumes of a burning incense stick placed at one corner of the room are perceived by smell at another corner of the room. What information about the motion of the gas molecules is available from this phenomenon?
Answer: Due to the mutual collisions of the gas molecules, there is a continuous change in their directions—this information is available from the given phenomenon.

Question 15. What is the number of molecules in 22.4 L of a gas at STP?
Answer: The number of molecules in 22.4 L of a gas at STP is 6.022 x10²³.

Question 16. How can the pressure of a certain quantity of a gas kept in a closed vessel and attached with a piston be increased without changing its temperature?
Answer: The pressure of gas inside the closed vessel increases if the piston is pushed inside the vessel, without changing the temperature.

Question 17. What is the difference between an ideal gas and a real gas on the basis of inter-molecular forces?
Answer: Though the value of intermolecular forces in the case of an ideal gas is zero, it is not so in the case of a real gas.

Question 18. Write down the ideal gas equation for n mol of a gas.
Answer: The ideal gas equation for n moles of a gas is pV=nRT.

Question 19. Write down the ideal gas equation for 1 mol of a gas.
Answer: The ideal gas equation for one mole of a gas is pV=RT.

Question 20. Is the equation pV = nRT applicable in the same way to all ideal gases?
Answer: Yes, the equation pV=nRT is applicable in the same way to all ideal gases.

Question 21. What is the unit of universal gas constant R in CGS system and SI?
Answer: The unit of universal gas constant R in CGS system and SI are erg. mol^-1 . K^-1 and J • mol^-1. K^-1, respectively.

Word Problems on Gas Laws with Solutions

Question 22. What is the value of universal gas constant R in cal . mol^-1. K^-1?
Answer: The value of universal gas constant in cal . mol^-1 . K^-1 is 1.987.

Question 23. What is the value of universal gas constant R in L . atm . mol^-1. K^-1 ?
Answer: The value of universal gas constant in L . atm . mol^-1. K^-1 is 0.082.

Question 24. What is the relation between the volume of the gas and the total volume of the molecules in case of an ideal gas?
Answer: In case of an ideal gas, total volume of the molecules of the gas is considered to be negligible as compared to the volume occupied by the gas.

Question 25. What is the nature of the collision between two molecules of an ideal gas?
Answer: The collision between two molecules of an ideal gas is an elastic collision because both linear momentum and kinetic energy are conserved in this case.

Question 26. What is the nature of the energy of gas molecules?
Answer: The gas molecules possess kinetic energy.

Question 27. What is condition of diffusion?
Answer:

Condition of diffusion

According to the condition of diffusion, when two or more gases which do not react with each other are kept in contact, they may undergo diffusion.

Question 28. Can diffusion take place against gravitation?
Answer: Yes, diffusion can take place against gravitation.

Question 29. A real gas can be converted into liquid by reducing its temperature. What can be inferred about intermolecular force from this phenomenon?
Answer: This phenomenon gives a preliminary idea about the intermolecular force in a real gas.

Question 30. Due to which condition of kinetics, the pressure of an ideal gas is greater than the pressure of a real gas under the same condition?
Answer: The condition that there is no attraction or repulsion amongst the molecules of an ideal gas is responsible for the given occurrence.

Question 31. What is the net attractive force on the molecules of a gas when it remains inside a vessel?
Answer: The net attractive force on the molecules of the gas is zero when it remains inside a vessel.

Question 32. When does a net attractive force act on the molecules of a gas inside a vessel?
Answer: A net attractive force acts on the molecules of a gas inside a vessel when they are very close to the wall of the vessel.

Question 33. Is it possible to convert an ideal gas into a liquid?
Answer: As there is no attractive force amongst the molecules of the ideal gas, hence it is not possible to convert an ideal gas into a liquid.

Question 34. Is it possible to convert a real gas into a liquid?
Answer: As attractive forces are present amongst the molecules of the real gas, it is possible to convert a real gas into a liquid.

Chapter 2 Behaviour Of Gases Topic B Combination Of Boyle’s Law And Charles’ Law, Ideal Gas Equation, Avogadro’s Law Fill In The Blanks

Question 1. There is _______    force of attraction between the molecules of an ideal gas.
Answer: No

Question 2. If the pressure of a definite mass of gas is quadrupled at constant temperature, ________ becomes one-fourth.
Answer: Volume

Question 3. The mass of 2 mol of CO₂ at STP is __________.
Answer: 88g

Question 4. The volume of 4 g of H₂ at STP is ________.
Answer: 44.8 L

Question 5. The molar mass of water is ________.
Answer: 18 g. mol^-1

Question 6. The value of molar volume does not depend on _________ of the gas.
Answer: Nature

Question 7. If the number of molecules present in 2 g of H₂ at STP is N, then the number of molecules present in 64 g of O₂ at STP is_______.
Answer: 2N.

Question 8. If the Avogadro number is N, then number of molecules present in 8.5g of NH₃ gas is _________.
Answer: N/2

Question 9. If the temperature of an enclosed gas increases, then kinetic energy of the molecules also ________.
Answer: Increase

Question 10. Compared to the time required by a gas molecule to traverse its free path, the time of collision is ________.
Answer: Neglible

Question 11. During collision of two molecules, both linear momentum and ___________ are conserved.
Answer: Kinetic Energy

Question 12. Force of attraction _________ between molecules of a real gas.
Answer: Exists

Question 13. The value of for one mole of an ideal gas is_________.
Answer: R

Question 14. Moist air is __________ than dry air.
Answer: Lighter

Question 15. In the equation \(p V=\frac{W}{M} R T\), M is the ___________.
Answer: Molar Mass

Question 16. Unit of molar mass in CGS system is _______.
Answer: g. mol^-1

Chapter 2 Behaviour Of Gases Topic B Combination Of Boyle’s Law And Charles’ Law, Ideal Gas Equation, Avogadro’s Law State Whether True Or False

Question 1. One mole of any gas at STP occupies 22.4 L volume and 6.022 x 10²³ molecules.
Answer: True

Question 2. The value of molar volume depends upon the nature of the gas.
Answer: False

Question 3. Real gases behave like ideal gases at low pressure and high temperature.
Answer: True

Question 4. Mean free path of a gas molecule is inversely proportional to the number of molecules per unit volume.
Answer: True

Question 5. The collision between two molecules of an ideal gas is an inelastic collision.
Answer: True

Question 6. The value of universal gas constant in L atm. mol^-1 . K^-1 is 0.082.
Answer: True

Question 7. Dimensional formula for universal gas constant is \(M L^2 T^2 N \Theta^{-1}\).
Answer: True

Question 8. In case of an ideal gas, volume of the gas molecules is neglected.
Answer: True

Question 9. At constant pressure, the density of a gas is inversely proportional to its absolute temperature.
Answer: True

Question 10. The value of R in the equation pV=RT depends on the values of p, V, and T.
Answer: True

Question 11. The total kinetic energy of the molecules gas at 0 K is zero.
Answer: True

Chapter 2 Behaviour Of Gases Topic B Combination Of Boyle’s Law And Charles’ Law, Ideal Gas Equation, Avogadro’s Law Numerical Examples Useful Relations

1. Combination of Boyle’s law and Charles’ law: \(\frac{p_1 V_1}{T_1}=\frac{p_2 V_2}{T_2}\)
where V₁, p₁ and T₁(K) are respectively initial volume, pressure and temperature, and V₂, p₂ and T₂(K) are respectively final volume, pressure and temperature T₂(K) of a gas of fixed mass

2. Avagadro’s law: \(\frac{V_1}{n_1}=\frac{V_2}{n_2}\)
where, under the condition of same temperature and pressure n₁ moles of a gas occupies volume V₁ and n₂ volume of the gas occupies the volume V₂.

3. Equation of state for n moles of an ideal gas:
pV=nRT, where p,V,T and R are pressure, volume, absolute temperature and universal gas constant respectively.

4. At STP molar volume of any gas is 22.4 L or 22400 mL.

5. Avogadro number: N_A = 6.022 x 1023

Question 1. Find the number of molecules in 22 g of CO₂ and 9 g of water.
Answer: Avogadro number, N = 6.022 x 10²³
Molar mass of C02 = 44 g
∴22 g of CO₂ = mol CO₂ = mol CO₂

So, the number of molecules in 22 g of CO₂ = \(\frac{N}{2}=\frac{6.022 \times 10^{23}}{2}=3.011 \times 10^{23}\)
Again, molar mass of H₂O = 1/2 mol H₂O
∴ 9g H₂O = 9/18 mol H₂O= 1/2 mol H₂O
Hence, number of molecules in 9 g of H₂O = \(\frac{N}{2}=\frac{6.022 \times 10^{23}}{2}\) = 3.011 x 10²³

Question 2. What is the molar mass of N₂ if the mass of 5.6 L of N₂  at STP is 7 g?
Answer: Mass of 5.6 L of N₂ gas at STP = 7g
∴ mass of 1L of N₂ gas at STP = \(\frac{7}{5.6}\)g and mass of 22.4 L of N₂ gas at STP = \(\frac{7}{5.6} \times 22.4\) = 28 g
So, molar mass of N2 = 28 g .

Question 3. what is the mass of 3 mol of NH3 gas? What is the volume of that quantity of gas at STP?
Answer: Molar mass of NH₃ = (14 +1 x 3)g = 17g
∴ mass of 3 mol of NH₃ gas = 17 x 3g = 51g
The volume of 3 mol of NH₃, gas at STP = 22.4 X3L = 67.2 L

Question 4. How many molecules are present in 1g of N₂ gas?
Answer: Molar mass of N₂ = 28 g
Avogadro number, N = 6.022 x 10²³
Now, there are 6.022 x 10²³  molecules present in 28 g of N₂ gas.
Hence, number of molecules in 1g of N₂ gas  \(\frac{6.022 \times 10^{23}}{28}=2: 15 \times 10^{22}\)

Question 5. Between 2 mol of N₂ and 1 mol of NH₃, which one has more atoms?
Answer: Number of atoms in one molecule of N₂ = 2
Thus, number of atoms in 2 mol of N₂ gas = 2 X 6.022 x 10²³ X 2 = 24.088 x 10²³
Number of atoms is one molecule of NH₃ = 4
Thus, the number of atoms in 1 mol of NH₃ gas = 4 X 6.022 X 10²³= 24.088 x 10²³
Hence, both 2 mol of N₂ and 1 mol of NH₃ contain the same number of atoms.

Question 6. The volume of a gas is 256 cm3 at 30°C temperature and a pressure of 108 cm Hg. What Is the volume of the gas at 0°C temperature and 76 cm Hg pressure?
Answer: Initial pressure of the gas (p₁)= 108 cm

Initial temperature (T₁) = 30 + 273 = 303 K

Initial volume (V₁) = 256 cm³

Final pressure (p₂) = pressure of 76 cm Hg

Final temperature (T₂) = 0 + 273 = 273 K

Now, suppose the final volume of the gas = V₂

so, \(\frac{p_1 V_1}{T_1}=\frac{p_2 V_2}{T_2}\) or, \(\frac{108 \times 256}{303}=\frac{76 V_2}{273}\) or, V₂ = 327.77 cm³

Therefore, final volume of the gas, V₂ = 327.77 cm³  

Question 7. The temperature of a gas of a certain mass is 27°C. The gas is heated in such a way that its pressure and volume are doubled. Calculate the final temperature of the gas.
Answer: Initial temperature (T₁) of the gas = 27 + 273 = 300 K

If the initial pressure of gas, p₁ = p, and initial volume V₁ = V, then the final pressure, p₂ = 2p and final volume, V₂ = 2 V.

Suppose, the final temperature of the gas is T₂ Thus by combining Charles’ law and Boyle’s law, we get

\(\frac{p_1 V_1}{T_1}=\frac{p_2 V_2}{T_2}\)  or, \(\frac{p V}{300}=\frac{2 p \times 2 V}{T_2}\)

Hence, the final temperature of the gas in Celsius scale = (1200- 273)°C = 927°C

Question 8. The volume of a gas at 5TP is 10 L. Calculate the number of moles of the gas
Answer: Pressure of gas (p) = 1 atmosphere

Volume (V) = 10 L

Temperature (T) = 273 K

Universal gas constant (R) = 0.08205 L . atm. mol^-1 . K^-1

If n is the number of moles of the gas, then we get from ideal gas equation, pV= nRT or, n=pV/RT

or, \(n=\frac{1 \times 10}{0.08205 \times 273}\) = 0.446

An alternative method:
The volume of 1 mol of gas at STP = 22.4 L

Hence, number of moles of the gas,

n = 10/22.4 = 0.446

Question 9. Find the mass of 8.31 L of methane gas at 127°C and 5 atmospheric pressure. Given, molar mass of methane gas = 16 g. mol^-1, density of mercury = 13.6 g/cm³
Answer: volume of methane gas (V) = 8.31L = 8.31 × 1000 cm³

Temperature (T) = 127 + 273 = 400K

Pressure (p) = 5 atm = 5 × 76 × 13.6 × 980 Dyn/cm³

Molar mass (M) = 16 g . mol^-1

Let us assume that the mass of methane gas = W

From ideal gas equation, \(p V=\frac{W}{M} R T\) or, \(W=\frac{p V M}{R T}\)

or,  \( W=\frac{5 \times 76 \times 13.6 \times 980 \times 8.31 \times 1000 \times 16}{8.31 \times 10^7 \times 400}\) = 20.26g (approx).

Chapter 2 Behaviour Of Gases Miscellaneous Type questions Match The Columns

Question 1. Different Curves are given in column A. Match the curves with their respective natures given in column B.

Column A	Column B
pV-p	1.  Straight line passing through the origin
p-V	2. Straight line passing parallel to the pressure axis
V-t	3. Straight line not passing through the origin
V-T	4. Rectangular hyperbola

Answer:
pV-p:  2. Straight    line    passing parallel to the pressure axis

p-V: 4. Rectangular hyperbola

V-t: 1.  Straight    line    passing through the origin

V-T:  3. Straight line not passing through the origin

Column A	Column B
Unit of rate of diffusion	1. 105 N . m-2.
1 pa = ______	2. erg. mol1 . K-1
Unit of the universal gas constant	3. 10 Dyn. cm-2
1 bar = _______	4. m3. s-1

Answer:
Unit of rate of diffusion: 4. m³. s^-1

1 p_a = ______: 3. 10 Dyn. cm^-2

Unit of the universal gas constant:  2. erg. mol¹ . K^-1

1 bar = _______: 1. 10⁵ N . m^-2.

WBBSE Solutions for Class 10 Physical Science and Environment