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Metallurgy Topic A Ores, Minerals And Alloys Synopsis

WBBSE Class 10 Metallurgy Overview

1. Metals such as, iron, copper, zinc, aluminium etc., have immense practical applications in our daily life.
2. Naturally occurring inorganic substances derived from the earth’s crust which contain metals in their free state or in the form of compounds along with earthy and rocky impurities are called minerals.
3. Minerals from which high-grade metals can be conveniently and economically extracted on a large scale are called ores.
4. All ores are minerals, but all minerals are not ores.
5. A homogeneous or heterogeneous mixture of two or more metals or a metal and a nonmetal having different characteristic properties than the constituent elements is called an alloy.
6. Alloys are stronger, have greater tensile strength and are less reactive than the individual constituent metals or non-metals. These properties make them less susceptible towards corrosion and weathering.

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

Metallurgy Topic A Ores, Minerals And Alloys Short And Long Answer Type Questions

Question 1. Classify iron on the basis of carbon content. Which among these is the purest?

Answer:

Classification Of iron on the basis of carbon content

1. On the basis a carbon content, iron is divided into three categories—cast iron (C: 2-4.5%), wrought iron (C: 0.1-0.15%) and steel (C: 0.151.5%).
2. Wrought iron is the purest form of iron.

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Question 2. Write some uses of cast iron.

Answer:

Cast iron is used in the making of

1. Wrought iron and steel
2. Tubes, iron, railing, cauldron, lamp post etc.

Question 3. Write some uses of wrought iron.

Answer:

Wrought iron is used in the making of

1. Core of electromagnet
2. Wires, nails, rods, chains etc.

Wbbse Class 10 Physical Science Solutions

Question 4. Write some uses of steel.

Answer:

Some uses of steel:

Steel finds extensive use in modern civilization. It is used in the making of
1. Automobiles, rails, knives, scissors, surgical instruments, ships, blades tankers etc.
2. Cooking utensils,
3. Alloy steel is made by adding other metals with steel.

Question 5. Why is copper used in the making of electrical wires and instruments?

Answer: Copper is a metal of low resistance and high malleability. Thus, it has a high value of electrical conductance and also it can be easily shaped into wires . Hence, it is used in the making of electrical wires and instruments.

Understanding the Extraction of Metals from Ores

Question 6. Copper is a good conductor – of heat— state one application of this property.

Answer:

Copper is a good conductor – of heat

1. Copper is used in making cooking utensils because it is a good conductor of heat.
2. Copper is used in the construction of a calorimeter which is quite helpful in measuring the amount of absorbed or released heat.
3. Copper is used in the making of boilers in factories. Being a good conductor it helps in boiling of water quickly.

Wbbse Class 10 Physical Science Solutions

Question 7. Write some important uses of zinc.

Answer:

Some important uses of zinc:

1. Zinc is used as a reagent in the laboratory for the preparation of hydrogen.
2. It is used in electrochemical cells and batteries.
3. It is also used in making of zinc white.
4. Zinc is coated over iron to protect it from rusting.

Question 8. Aluminium is a light non-corrosive metal—state application of this property.

Answer:

Aluminium is a light non-corrosive metal

1. Being a light metal aluminium is used in the manufacture of body parts of machines.
2. As it is non-corrosive and light, it is used in making the body of automobiles, aeroplanes, window frames, buckets, tanks, boxes etc.

Question 9. Some properties of aluminium are mentioned below. State the applications of these properties.
1. Aluminium is a good conductor of electricity.
2. Aluminium can be easily beaten into thin sheets.

Answer:
1. Aluminium is a good conductor of electricity. Hence, it is used for making electrical wires and electrical instruments.
2. Aluminium can be easily beaten into thin sheets. Due to this property, aluminium is used in making packing foils.

Wbbse Class 10 Physical Science Solutions

Question 10. What is an alloy? Name a common alloy and state its composition.

Answer:

Alloy:

1. An alloy is a homogeneous or heterogeneous mixture of two or more metals or sometimes of metals and non-metals having characteristic properties different from their constituent elements.

A common alloy

2. A common and widely used alloy is brass. It is made of copper (60-80%) and zinc (20-40%).

 

 

Steps in the Metallurgical Process

Question 11. State two important characteristics of alloys.

Answer:

Some important characteristics of alloys are discussed below—

1. An alloy may be homogeneous or heterogeneous in nature.
2. An alloy has different characteristic properties than its constituent metals.

Wbbse Class 10 Physical Science Solutions

Question 12. Write down the advantages of using alloys.

Answer:

The advantages of using alloys are—

1. Alloys have more tensile strength than their constituent elements. E.g., brass or bell metal is more tensile than copper.
2. Metals melt at very high temperatures. When a pure metal is alloyed with another metal or non-metal, its melting point generally reduces.
3. Metals are extremely susceptible to chemical and weather attacks. Alloys are more resistant to corrosion. When a metal is alloyed, it becomes less reactive, thereby enhancing its corrosion resistance.
4. To increase or decrease the conductivity of metals, alloying can be done. E.g., specific resistance of nichrome is greater than its component metals, i.e., conductivity of nichrome is less than that of its component metals and thus it is used in an electric heater.

Question 13. Name two alloys of iron, state their compositions and mention some uses of these alloys.

Answer:

Composition and uses of alloys of iron are:

Alloy	Composition	Uses
Stainless steel	Fe: 73%, Cr: 18%, Ni: 8%, C: 1%	In making of utensils, knife, scissors, surgical instruments, machine parts etc.
Nickel steel	Fe: 96-98%, Ni: 2-4%	Manufacturing automobile parts, gear, propellers of aircraft, cables etc.

Question 14. Give the composition And uses of two alloys containing both copper and zinc as their constituents.

Answer: Brass and bronze contain both copper and zinc as their constituents.

Wbbse Class 10 Physical Science Solutions

Alloy	Composition	Uses
Brass	Cu: 60-80%, Zn: 20-40%	Making parts of telescopes, barometer etc., utensils, pipes, statues etc.
Bronze	Cu: 80%, Sn: 18%, Zn: 2%	Making statues, coins, utensils, medals etc.

Question 15. Write down the name of the main component of brass. Why is the use of brass more advantageous than that of its main component?

Answer:

The main component of brass is copper (Cu: 6080%, Zn: 20-40%). The advantages of using brass compared to copper are as follows—

1. Brass has more tensile strength than soft metal copper.
2. Reactivity of brass is less than that of copper and hence brass is less corrosive in nature.

Question 16. Write down the name, composition and uses of some alloys of aluminium.
Answer:

The name, composition and uses of some alloys of aluminium are—

Alloy	Composition	Use
Magnelium	Al = 90-95%, Mg = 5-10%	Parts of aeroplanes, balance and scientific apparatus are made with magnelium.
Duralumin	Al = 95%, Cu = 4%, Mg = 0.5%, Mn = 0.5%	Parts of aeroplane and motor car, pressure cookers are made with duralumin.
Aluminium- bronze	Al = 10%, Cu = 90%	Coin, statues, flower vases, and cooking utensils are made with aluminium bronze.
Alnico	Fe = 60%, Ni = 20%, Al = 12%, Co = 8%	Permanent magnets of high power are made with alnico.

Question 17. What do you mean by amalgam and give example; Mention some uses of mercury alloys.

Answer:

Amalgam:

The alloys which contain mercury (Hg) as one of their constituents are commonly known as amalgams. E.g., sodium amalgam (Na-Hg), magnesium amalgam (Mg-Hg) etc.

The uses of mercury alloys, i.e., amalgams are as follows—
1. Tin-amalgam (Sn-Hg) is used in the preparation of the mirror.
2. Sodium-amalgam (Na-Hg) and zinc-amalgam (Zn-Hg) are used as reagents (reductants) in organic reactions.
3. Silver amalgam (Ag-Hg) is used in dental treatment.

Question 18. Define minerals and give examples.

Answer:

Minerals:

Minerals may be defined as the naturally occurring inorganic substances found in the earth’s crust or on earth surface which contains metals in their native state or in the form of compounds mixed with other impurities. For example—red haematite (Fe₂O₃), magnetite (Fe₂O₄), and iron pyrites (FeS₂) are minerals containing iron.

 

Common Methods of Concentrating Ores

Question 19. Define ores and give examples.

Answer:

Ores:

The minerals from which a metal can be conveniently and economically extracted are known as ores of the metal. For example—High quality iron can be conveniently and economically extracted from red haematite (Fe₂O₃). Hence, red haematite is an ore of iron.

Similarly, malachite [CuCO₃ • Cu(OH)₂ ] is an ore of copper.

Question 20. Differentiate between monerals and ores.

Answer:

The major differences between minerals and ores are:

Minerals	Ores
Minerals    are inorganic substances found in the earth’s crust containing one or more metals, in their native state or as their compounds, along with impurities. For example, copper pyrites (Cu2S-Fe2S3) is a mineral of copper.	The minerals from which a metal can be conveniently and    economically extracted involving less complex-    chemical methods are called ores of that metal. For example, red haematite (Fe2O3) and iron pyrites (FeS2) both are minerals of iron but only iron pyrites is the ore of iron not haematite.
All minerals are not ores.	All ores are minerals.

Question 21. All ores are minerals, but all minerals are not ores – justify the statement.

Answer:

All ores are minerals, but all minerals are not ores

Minerals are the naturally occuring inorganic substances which contain one or more metals, in their native state or as their compounds, along with impurities.

On the other hand, the minerals from which a metal can be conveniently and economically extracted are called ores of that metal. Obviously, all ores are minerals.

But, we cannot extract metals from any mineral by convenient and cheap methods. Hence, all minerals cannot be called ores.

For example, both bauxite and china-clay are the minerals of aluminium. But, only bauxite is considered as the ore of aluminium, not china-clay.

Question 22. Why zinc belend can be termed as both mineral and ore?

Answer: Zinc blend (ZnS) is a solid metal compound which can be found in earth crust or in mines. Hence it can be termed as mineral of zinc. Moreover, high quality metallic zinc can be extracted from zinc blend using easier metallurgical technique. Hence zinc blend can be termed as ore of zinc metal, too.

Question 23. Write down the name and formula of important ores of copper.

Answer:

Name and formula of important ores of copper are

Oxide ore — cuprite (Cu₂O)
Sulphide ore — copper pyrites (Cu₂S-  Fe₂S₃ or CuFeS₂), copper glance – (Cu₂S)
Carbonate ore — malachite [CuCO₃ • Cu(OH)₂]

Question 24. Write down the names of important ores of iron.

Answer:

The names of important ores of iron are

Oxide ore — red haematite (Fe₂O₃), magnetite (Fe₂O₄)
Carbonate ore — spathic iron orsedarite (Fe₂O₃)

Question 25. Write down the names of important ores of zinc.

Answer:

The names of important ores of zinc are

Oxide ore — zincite (ZnO)
Sulphide ore — zinc blend (ZnS)
Carbonate ore — calamine (ZnCO₃)

Question 26. Write down the names of important ores of aluminium.

Answer:

The names of important ores of aluminium

Oxide ore — bauxite ( Al₂O₃ • H₂O), gibbsite (Al₂O₃-3H₂O)
Fluoride ore — cryolite (AIF₃ • 2NaF)

Metallurgy Topic A Ores, Minerals And Alloys Very Short Answer Type Questions Choose The Correct Answer

Question 1. The core of an electromagnet is made of

1. Cast iron
2. Steel
3. Wrought iron
4. Magnetite

Answer: 3. Wrought iron

Question 2. The metal used in making of electrolytic cells and dry cells is

1. Al
2. Sn
3. Zn
4. Cu

Answer: 3. Zn

Question 3. Which of the following is the purest form of iron?

1. Cast iron
2. Wrought iron
3. Steel
4. Invar

Answer: 2. Wrought iron

Question 4. The amount of carbon present in steel is

1. 0.01-0.2%
2. 0.15-1.5%
3. 2-4.5%
4. 5-5.6%

Answer: 2. 0.15-1.5%

Question 5. Which of the following is not a constituent of the alloy, duralumin?

1. Copper
2. Magnesium
3. Manganese
4. Nickel

Answer: 4. Nickel

Question 6. The percentage of silver in German silver is

1. 2-5%
2. 5-10%
3. 10-15%
4. 0%

Answer: 4. 0%

Question 7. Which of the following alloys does not contain zinc as a constituent metal?

1. Brass
2. German silver
3. Bell metal
4. Gem metal

Answer: 3. Bell metal

Question 8. Which of the following alloys does not contain nickel as a constituent metal?

1. Stainless steel
2. Manganese steel
3. German silver
4. Invar

Answer: 2. Manganese steel

Question 9. Which of the following minerals is not an ore?

1. Red haematite
2. Zinc blende
3. Bauxite
4. Iron pyrites

Answer: 4. Iron pyrites

Question 10. The oxide ore of zinc is

1. Calamine
2. Zinc blende
3. Zincite
4. Willemite

Answer: 3. Zincite

Question 11. Tin-amalgam is used

1. To make spectacles
2. As a reducing agent
3. To make mirrors
4. To make thermometers

Answer: 3. To make mirrors

Question 12. Which of the following is a mineral of iron but not its ore?

1. Red haematite
2. Magnetite
3. Iron pyrites
4. Siderite

Answer: 3. iron pyrites

Question 13. Gibbsite is the ore of

1. Al
2. Cu
3. Zn
4. Fe

Answer: 1. Al

Question 14. Calamine is the ore of

1. Iron
2. Copper
3. Zinc
4. Aluminium

Answer: 3. zinc

Question 15. Components of German silver are

1. Cu, Zn, Sn
2. Al, Cu, Mg, Mn
3. Fe, Cr, Ni, C
4. Cu, Zn, Ni

Answer: 4. Cu, Zn, Ni

Question 16. Which one of the following is the ore of aluminium?

1. Red haematite
2. Malachite
3. Chalcopyrites
4. Bauxite

Answer: 4. Bauxite

Question 17. Main component of duralumin is

1. Al
2. Mg
3. Cu
4. Sn

Answer: 1. Al

Question 18. Chalcopyrites is the ore of

1. Zn
2. Fe
3. Mg
4. Cu

Answer: 4. Cu

Question 19. Which of the following is a sulphide ore?

1. Bauxite
2. Zincite
3. Haematite
4. Zinc blende

Answer: 4. Zinc blende

Question 20. Composition of brass is

1. Cu and Sn
2. Zn and Cu
3. Cu and Pb
4. Cu and Al

Answer: 2. Zn and Cu

Question 21. Which of the following is not an ore of Cu?

1. Haematite
2. Chalcocite
3. Azurite
4. Malachite

Answer: 1. Haematite

Question 22. Which of the following metal pair is present in both bronze and bell metal?

1. Iron, nickel
2. Copper, tin
3. Zinc, copper
4. Iron, tin

Answer: 2. Copper, tin

Question 23. Among the components of amalgam, one must be

1. Fe
2. Ag
3. Au
4. Hg

Answer: 4. Hg

Question 24. The amount of carbon is highest in

1. Steel
2. Wrought iron
3. Cast iron
4. Chrome steel

Answer: 3. Cast iron

Question 25. The alloy used in preparation of the structure of aeroplane is

1. German silver
2. Bronze
3. Invar
4. Duralumin

Answer: 4. Duralumin

Question 26. Haematite is the ore of

1. Copper
2. Aluminium
3. Iron
4. Zinc

Answer: 3. Iron

Question 27. Which one of the following metal is present in china clay?

1. Cu
2. Al
3. Fe
4. Zn

Answer: 2. Al

Question 28. Which one of the following contains aluminium?

1. Bronze
2. Bell metal
3. German silver
4. Duralumin

Answer: 4. Duralumin

Question 29. Percentage of carbon in wrought iron is

1. 0.1-0.15%
2. 0.16-0.6%
3. 2-2.5%
4. 3-3.5%

Answer: 1. 0.1-0.15%

Question 30. The main component of magnelium is

1. Mn
2. Al
3. Mg
4. C

Answer: 2. Al

Question 31. Which one of the following alloys contains zinc?

1. Bell metal
2. Brass
3. Bronze
4. Duralumin

Answer: 2. Brass

Metallurgy Topic A Ores, Minerals And Alloys Answer In Brief

Question 1. Arrange wrought iron, steel and cast iron in the order of increasing carbon content present in them.
Answer: Wrought iron < steel < cast iron.

Question 2. Which metal is present in each of bronze, brass and bell metal?
Answer: In each of bronze, brass and bell metal, copper is present.

Question 3. What are the major constituents of stainless steel?
Answer: The major constituents of stainless steel are iron (73%), chromium (18%) and nickel (8%).

Question 4. Name any two alloys of aluminium.
Answer:

Two alloys of aluminium are—

1. Magnelium (Mg, Al) and
2. Alnico (Al, Ni, Co, Fe).

Question 5. Name any two alloys of iron.
Answer:

Two alloys of iron are—

1. Stainless steel (Fe, Cr, Ni and traces of carbon) and
2. Invar(Fe, NO.)

Question 6. Name any two alloys of zinc.
Answer:

Two alloys of zinc

Two alloys of zinc are 0 brass (Cu, Zn) and 0 german silver (Cu, Zn, Ni).

Question 7. Name some important ores of iron.
Answer: Some important ores of iron are red haematite (Fe₂O₃), magnetite (Fe₂O₄), siderite (Fe₂O₃) etc.

Question 8. Name some important ores of copper with their formulas.
Answer: Some important ores of copper are copper pyrites [(Cu₂S • Fe₂S₃) or CuFeS₂], copper glance (Cu₂S), malachite [CuCO₃ • Cu(OH)₂] , cuprite (Cu₂O) etc.

Question 9. Name the major ores of zinc with their respective formulas.
Answer: The major ores of zinc are zinc blende (ZnS), calamine (ZnCO₃), zincite (ZnO) etc.

Question 10. Name the major ores of aluminium with their respective formulas.
Answer: The major ores of aluminium are bauxite. (Al₂O₃-2H₂O), gibbsite (Al₂O₃ • 3H₂O), cryolite (AlF₃• 3NaF) etc.

Question 11. Name a mineral of aluminium which is not considered as its ore.
Answer: China-clay ( Al₂O₃ • 2SiO₂• 2H₂O) is a mineral of aluminium but is not considered as its ore.

Question 12. Name a metal which is found in nature in its free state.
Answer: Gold (Au) is found in nature in its free state.

Question 13. Why is invar used in making metre scale?
Answer: Invar is used in making metre scale because its coefficient of linear expansion is very small.

Question 14. What are noble metals? Give examples.
Answer: The metals which are chemically not so reactive are known as noble metals. Example: Gold, platinum.

Question 15. Write down the percentage of carbon in wrought iron.
Answer: The percentage of carbon in wrought iron is 0.1-0.15%.

Question 16. Which type of iron is used to prepare electric iron?
Answer: Cast iron is used to prepare electric iron.

Question 17. Which metallic powder is mixed with ammonium nitrate to prepare the explosive called ‘ammonal’?
Answer: Aluminium powder.

Question 18. Why is copper used as an electrode in electrical cells?
Answer: Due to its high electrical conductivity.

Question 19. Which metal is used to prepare calorimeter and why?
Answer: Copper, due to its high conductivity of heat, is used to prepare calorimeter.

Question 20. Which metal is used in print-block?
Answer: Zinc is used to prepare print blocks.

Question 21. Mention the metallic components of bronze?
Answer: Copper (80%), tin (18%) and zinc (2%).

Question 22. Name the metal pair which is present in both of bronze and bell metal.
Answer: Copper and tin.

Question 23. Which metal is common in brass and bronze?
Answer: Copper.

Question 24. Name the non-transition metal present in bell-metal.
Answer: Tin (Sn).

Question 25. Percentage of which metal is higher in brass?
Answer: Copper (60-80%).

Question 26. Write down the composition of German silver.
Answer: Cu: 50%, Zn: 20%, Ni: 30%

Question 27. Write down the name of the main component of duralumin.
Answer: Aluminium (95%).

Question 28. Which alloy is used to prepare the structure of aeroplane?
Answer: Duralumin is used to prepare the structure of aeroplane

Question 29. Give examples of two alloys made up of four metals.
Answer: Duralumin (Al + Cu + Mn + Mg) and alnico (Fe + Ni + Al + Co).

Question 30. Which alloy is used to prepare permanent magnet?
Answer: Alnico (Fe + Ni + Al + Co).

Question 31. Which alloy is used to prepare pressure cooker?
Answer: Duralumin.

Question 32. Which one of iron pyrites and red haematite, is the ore of iron?
Answer: Red haematite is the ore of iron.

Question 33.Write down the name and formula of a substance which is a mineral of iron but not its ore.
Answer: Iron pyrites (FeS₂).

Question 34. Calamine is the ore of which metal?
Answer: Calamine (ZnCO₃) is the ore of zinc.

Question 35. Write down the formula of zinc white?
Answer: Chemical formula of zinc white is ZnO.

Question 36. Write down the formula of the ore— Gibbsite.
Answer: The formula of Gibbsite is Al₂O₃ • 3H₂O.

Metallurgy Topic A Ores, Minerals And Alloys Fill In The Blanks

Question 1. An explosive is prepared by mixing _______ powder with ammonium nitrate.
Answer: Aluminium

Question 2. The percentage of carbon in wrought iron is ______ %.
Answer: 0.1-0.15

Question 3. The non-metal present in stainless steel is _______
Answer: Carbon

Question 4. The carbonate ore of iron is ________
Answer: Siderite

Question 5. The amalgam of _______ metal is used as a reducing agent in organic reactions.
Answer: Sodium

Question 6. The alloy of aluminium used in making electromagnets is _______
Answer: Alnico

Question 7. Metals can be extracted conveniently and economically from their ______
Answer: Ores

Question 8. Cryolite is an ore of _______
Answer: Aluminium

Question 9. The oxide ore of copper is ______
Answer: Cuprite

Question 10. ________ foil is used for packaging of food.
Answer: Aluminium

Question 11. German silver is the alloy of ____ and nickel.
Answer: Copper(Cu₂O)

Question 12. Percentage of silver in German silver is _______
Answer: Zero

Question 13. The main component of duralumin is ______
Answer: Aluminium

Question 14. If one of the components of an alloy be mercury, then the alloy is termed as an ________
Answer: Amalgam

Question 15. ________ is the ore of aluminium.
Answer: Gibbiste/Bauxite

Question 16. All the ores are minerals, but all of the minerals are not _____
Answer: Ores

Question 17. Name of the sulphide ore of copper is ______
Answer: Copper glance

Question 18. Formula of baixite is _______
Answer: Al₂O₃ 

Metallurgy Topic A Ores, Minerals And Alloys State Whether True Or False

Question 1. All minerals are ores, but all ores are not minerals.
Answer: False

Question 2. Calamine is the chief ore of zinc.
Answer: True

Question 3. Cast iron is the purest form of iron.
Answer: False

Question 4. Zincite is the oxide ore of zinc.
Answer: True

Question 5. The percentage of silver present in the alloy German silver is 2-5%.
Answer: False

Question 6. Tin-amalgam is used to make spectacles.
Answer: False

Question 7. The alloy named invar is used to prepare metre-scale.
Answer: True

Question 8. A component of bell-metal is zinc.
Answer: False

Question 9. Components of brass are Cu and Sn. Chalcosite is the ore of copper.
Answer: False

Question 10. Chalcosite is the ore of copper.
Answer: True

Metallurgy Topic B Principles Of Metal Extraction And Oxidation-Reduction Synopsis

 

1. A chemical reaction in which an atom, an ion or a molecule loses one or more electrons is called an oxidation reaction.
2. A chemical reaction in which an atom, an ion or a molecule gains one or more electrons is called a reduction reaction.
3. Extraction of a metal from its corresponding oxide by elimination of oxygen is known as reduction.
4. Extraction of metals such as iron, chromium, manganese etc., from their oxides by heating the oxides with aluminium powder at a high temperature is known as Goldschmidt’s thermite process.
5. A mixture of 3 parts of Al₂O₃ and 1 part of aluminium powder is known as thermite mixture.
6. The vertical arrangement of metals in decreasing order of their relative reactivity is known as metal activity series.
7. A metal occupying a higher position (more reactive) in the metal activity series can displace another metal occupying a relatively lower position(less reactive) from the aqueous solution of its salt.
8. Metals present in the middle of the activity series such as Zn, Fe etc., can be extracted from their ores by carbon reduction process.
9. Metals present at the top of the metal activity series are extracted by electrolysis of their fused salts.

Metallurgy Topic B Principles Of Metal Extraction And Oxidation-Reduction Short And Long Answer Type Questions

 

Question 1. How does oxidation occur?

Answer:

Oxidation takes place in three different ways—

1. Oxidation takes place when an atom loses electron(s).
Example—\(\mathrm{Na}+\rightarrow \mathrm{Na}^{+}+e ; \mathrm{Al} \rightarrow \mathrm{Al}^{3+}+3 e\)

2. Oxidation takes place when a cation loses electron(s).
Example— \(\begin{aligned}
& \mathrm{Cu}^{+} \rightarrow \mathrm{Cu}^{2+}+e \\
& \mathrm{Fe}^{2+} \rightarrow \mathrm{Fe}^{3+}+e
\end{aligned}\)

3. Oxidation takes place when an anion loses an electron(s).
Example— \(\mathrm{S}^{2-} \rightarrow \mathrm{S}+2 e ; 2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_2+2 e\)

Question 2. How does reduction occur?

Answer:

Reduction takes place in four different ways—

1. Reduction takes place when an atom accepts electron(s).
Example: \(\mathrm{Cl}+e \rightarrow \mathrm{Cl}^{-} ; \mathrm{O}+2 e \rightarrow \mathrm{O}^{2-}\)

2. Reduction takes place when a cation accepts electron(s).

Example: \(\mathrm{Na}^{+}+e \rightarrow \mathrm{Na} ; \mathrm{Mg}^{2+}+2 e \rightarrow \mathrm{Mg}\)

3. Reduction takes place when an anion of lower charge accepts electron(s) and is converted into an anion of higher charge.

Example: \(\begin{aligned}
& \mathrm{MnO}_4^{-}+e \rightarrow \mathrm{MnO}_4^{2-} \\
& \mathrm{O}^{-}+e \rightarrow \mathrm{O}^{2-}
\end{aligned}\)

4. Reduction takes place when a cation of higher charge accepts electron and is converted into another cation of lower charge.

Example: \(\begin{aligned}
& \mathrm{Fe}^{3+}+e \rightarrow \mathrm{Fe}^{2+} ; \\
& \mathrm{Sn}^{4+}+2 e \rightarrow \mathrm{Sn}^{2+}
\end{aligned}\)

Question 3. Discuss the electronic theory of oxidation and reduction.

Answer:

The electronic theory of oxidation and reduction

Oxidation: The process of removal of one or more electrons from an atom or ion is known as oxidation.

Example: \(\mathrm{Na} \rightarrow \mathrm{Na}^{+}+e, \mathrm{Fe}^{2+} \rightarrow \mathrm{Fe}^{3+}+e\)

Reduction: The process of acceptance of one or more electrons by an atom or ion is known as reduction.

Example: \(\mathrm{Cl}+e \rightarrow \mathrm{Cl}^{-}, \mathrm{Na}^{+}+e \rightarrow \mathrm{Na}\)

Question 4. Identify which one is oxidation and which one is reduction— \(\mathrm{Ca} \rightarrow \mathrm{Ca}^{2+}+2 e ; \mathrm{O}+2 e \rightarrow \mathrm{O}^{2-}\)

Answer: \(\mathrm{Ca} \rightarrow \mathrm{Ca}^{2+}+2 e\) – In this reaction a Ca-atom loses two electrons to form Ca²⁺ ion. Hence it is an oxidation reaction as loss of electrons means oxidation.

\(\mathrm{O}+2 e \rightarrow \mathrm{O}^{2-}\) —In this reaction an O-atom gains two electrons to form O^2- ion. Since gaining of electrons is termed as reduction, so this reaction is a reduction process.

Question 5. With the help of electronic theory, show that oxidation and reduction occur simultaneously in the following reaction: \(2 \mathrm{Fe}^{3+}+\mathrm{Sn}^{2+} \rightarrow 2 \mathrm{Fe}^{2+}+\mathrm{Sn}^{4+}\)

Answer: \(2 \mathrm{Fe}^{3+}+\mathrm{Sn}^{2+} \rightarrow 2 \mathrm{Fe}^{2+}+\mathrm{Sn}^{4+}\)

 

Here each Fe³⁺ ion accepts an electron to form Fe²⁺ ion. Hence it is a reduction process as gaining of electron is termed as reduction.

\(\mathrm{Fe}^{3+}+e \rightarrow \mathrm{Fe}^{2+}\)

 

Again each Sn²⁺ ion loses 2 electrons from its valence shell. Hence the process is oxidation as losing of electron in termed as oxidation.

\(\mathrm{Sn}^{2+} \rightarrow \mathrm{Sn}^{4+}+2 e\)

 

Hence, it can be said that oxidation and reduction occur simultaneously.

Question 6. Extraction of metals from their ores is basically a reduction process—explain with example.

Answer:

Extraction of metals from their ores is basically a reduction process

In the ore, metal remains in a positive oxidation state but, after extraction of the metal, the oxidation number becomes zero. Thus, during extraction of the metal, the metal ion accepts electron to become a free atom. Hence, we can say that extraction of metals from its ores is a reduction process.

\(\mathrm{M}^{n+}(\text { metal ion })+\text { ne } \rightarrow \mathrm{M}(\text { free metal })\)

 

Example: Zinc oxide (ZnO) is mixed with excess coke and heated at a temperature of about 1300-1400°C in a retort when zinc oxide is reduced to metallic zinc.

\(\mathrm{ZnO}+\mathrm{C} \rightarrow \mathrm{Zn}+\mathrm{CO} \uparrow\)

Chemical Properties of Metals in Metallurgy

Question 7. What do you mean by metal activity series? Name the metals at the top and bottom of the series.

Answer:

Metal activity series:

1. The series obtained by vertically arranging the metals from top to bottom in decreasing order of their electropositivity or decreasing order of chemical reactivity is called metal activity series.
2. The metal placed at the top of the series is potassium (K) while gold (Au) is placed at the bottom.

Question 8. Arrange Cu, Fe, Ag and Zn in increasing order of their reactivity on the basis of the following reactions.
1. CuSO₄+ Fe → FeSO₄ + Cu
2. 2AgNO₃ + Cu → Cu(NO₃)₂+ 2Ag
3. FeSO₄ + Zn → ZnSO₄+ Fe

Answer: A more reactive metal replaces a less reactive metal from its salt. So, according to reaction,
1. Fe is more reactive than Cu. According to reaction,
2. Cu is more reactive than Ag. According to reaction,
3. Zn is more reactive than Fe

Hence, the order of increasing reactivity: \(\mathrm{Ag}<\mathrm{Cu}<\mathrm{Fe}<\mathrm{Zn}\)

Question 9. How are the metals placed at the top of the metal activity series extracted?

Answer: These metals are usually extracted by electrolytic method. The molten hydroxide or chloride salts of the metal is electrolysed using suitable electrodes, and the metal deposits on the cathode.

For example, sodium is extracted by electrolysing a molten solution of sodium chloride using iron cathode and graphite anode. Sodium is deposited at the cathode.

Dissociation of NaCI: \(\mathrm{NaCl} \text { (molten) } \rightarrow \mathrm{Na}^{+}+\mathrm{Cl}^{-}\)

Reaction at cathode: \(\mathrm{Na}^{+}+e \rightarrow \mathrm{Na}\)

Reaction at anode: \(\begin{aligned}
& \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}+e \text { (oxidation); } \\
& \mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{Cl}_2 \text { (reduction) }
\end{aligned}\)

Question 10. Describe the extraction of aluminium from pure alumina by electrolytic method.

Answer:

The extraction of aluminium from pure alumina by electrolytic method

Aluminium is generally extracted from bauxite ore  Al₂O₃ -2H₂O. At first, bauxite is converted into pure alumina. Pure alumina is then mixed with proportionate amount of cryolite (CaF₂) and fluorspar (AIF₃ • 3NaF) and the mixture is heated at around 900°C. When electricity is passed through the fused mixture, aluminium is deposited at the cathode.

Electrolytic dissociation: \(\left.\mathrm{Al}_2 \mathrm{O}_3 \text { (molten }\right) \rightarrow 2 \mathrm{Al}^{3+}+3 \mathrm{O}^{2-}\)

Cathode reaction: \(2 \mathrm{Al}^{3+}+6 e \rightarrow 2 \mathrm{Al}\)

Anode reaction: \(\begin{aligned}
& 3 \mathrm{O}^{2-} \rightarrow 3 \mathrm{O}+6 e \\
& 3 \mathrm{O}+3 \mathrm{O} \rightarrow 3 \mathrm{O}_2
\end{aligned}\)

Question 11. Why are the strong electropositive metals like Na, K etc., not extracted from the aqueous solution of their salts?

Answer: An aqueous solution of a salt of a strong electropositive metal contains H⁺ ions formed due to dissociation of water, along with the metal cations. Now, the tendency of H+ ions to be discharged at cathode is stronger than that of metals like Na, K etc.

Hence, on electrolysis of the aqueous solution, H+ ions will be reduced at cathode instead of metal ions. Hence, hydrogen gas will be produced at cathode instead of desired metal. This is why a strong electropositive metal is extracted from its salt by electrolysis of the fused salt but not the aqueous solution of the salt.

Question 12. Which method is suitably used for the extraction of metals (such as Fe, Zn etc.) occupying the middle part of the metal activity series? Explain with reasons.

Answer: The metals occupying the middle part of the metal activity series are moderately reactive and hence have relatively less tendency than carbon to combine with oxygen. Therefore, these metals can be extracted from their oxides by carbon reduction process at high temperature.

Example: \(\mathrm{ZnO}+\mathrm{C}(\text { coke }) \rightarrow \mathrm{Zn}+\mathrm{CO}\)

Applications of Metallurgy in Industry

Question 13. When an iron nail is dipped into an aqueous solution of copper sulphate, a reddish-brown layer is developed over the nail. Explain why.

Answer: A metal occupying a higher position relative to another metal in the metal activity series can replace the latter from the solution of it’s salt. In metal activity series, iron is placed above copper.

Hence iron can replace copper from copper sulphate solution. So, when an iron nail is dipped into an aqueous copper sulphate solution, reaction takes place between them at the surface of iron nail and hence a reddish brown layer of metallic copper is formed over the iron nail.

\(\mathrm{Fe}+\mathrm{CuSO}_4 \rightarrow \mathrm{FeSO}_4+\mathrm{Cu} \downarrow \text { (red) }\)

 

 

Question 14. What happens when a piece of zinc is added to an aqueous solution of copper sulphate?

Answer: In the metal activity series, zinc is placed above copper. Hence zinc can replace copper from copper sulphate solution. So, when a small piece of zinc is dipped in copper sulphate solution, reaction takes place between zinc and copper sulphate and copper is precipitated. The precipitated copper deposits on the surface of zinc and hence a reddish brown layer is formed over zinc.

\(\mathrm{Zn}+\mathrm{CuSO}_4 \rightarrow \mathrm{ZnSO}_4+\mathrm{Cu} \downarrow \text { (red) }\)

 

Question 15. What is carbon reduction process metal extraction?

Answer:

Carbon reduction process metal extraction

Reduction of a metal oxide by heating the mixture of metal oxide with carbon at a very high temperature in a blast furnace is called carbon reduction process. ‘Coke powder’ is used as a reducing agent for this process. Besides, CO produced due to incomplete oxidation of carbon also acts as reducing agent.

Question 16. Aluminium cannot be extracted by carbon reduction process. Explain with reasons.

Answer:

Aluminium cannot be extracted by carbon reduction process.

Aluminium occupies the top portion of the metal activity series. Hence, it is a highly reactive metal and possesses strong reducing property. Carbon reduction process is applicable for the extraction of those metals which have relatively greater tendency to combine with carbon than oxygen.

However, aluminium has a greater tendency to combine with oxygen than carbon and also the oxide of aluminium (Al₂O₃) is more stable as compared to the oxides of carbon. Thus aluminium cannot be extracted by carbon reduction process. Al is generally extracted by electrolysis of molten alumina (Al₂O₃).

Question 17. How is zinc extracted by carbon reduction process?

Answer: During zinc extraction by carbon reduction process, the zinc ore, i.e., zinc blende (ZnS) or calamine (ZnCO₃) is converted into zinc oxide. Zinc oxide is then mixed well with excess coke powder.

The mixture is then taken in a retort made of fireclay and heated at a temperature of about 1300-1400°C. At this temperature zinc oxide is reduced to metallic zinc and carbon monoxide (CO) is evolved.

\(\mathrm{ZnO}+\mathrm{C} \rightarrow \mathrm{Zn}+\mathrm{CO} \uparrow\)

 

Coke acts as a reducing agent in this reaction.

Question 18. Write down advantages and disadvantages of carbon reduction process.

Answer:

Advantages of carbon reduction process:

1. The reductant used in this process, i.e., coke, is easily available and cheap.
2. Large amount of metal oxide can be reduced using a comparatively smaller amount of coke.
3. CO gas, formed in the reaction acts as reducing agent in addition to coke, in this process.

Disadvantages of carbon reduction process:

1. Highly electropositive metals like Na, K, Al, Mg etc., cannot be extracted by this process.
2. A few metals like Ca, Al etc., react with coke at higher temperature to form carbide compounds.

Question 19. Describe the principle of thermite process with example.

Answer:

The principle of thermite process with example:

Al has strong affinity for oxygen at high temperature. When oxides of relatively less reactive metals such as Fe, Mn, Cr etc., are heated with Al powder at a very high temperature, the oxides are reduced by Al to the corresponding metal.

This is the basic principle of Goldsmith’s thermite process. The process produces large amount of heat and the reaction temperature reaches as high as 2000°C. At this temperature, the extracted metal is obtained in molten state.

 

Question 20. What is thermite mixture? Write two practical applications of thermite process.

Answer:

Thermite mixture

A mixture of 3 parts of ferric oxide (Fe₂O₃) by mass with 1 part of powdered aluminium is known as thermite mixture.

Some important applications of thermite process are discussed below—

1. Thermite process is applied in repairing broken parts of rails, tram lines, ship, machines made of iron etc.
2. Metals like chromium, manganese etc., are extracted by thermite process.

Question 21. What is used as reducing agent in thermite process? What is ignition mixture?

Answer:

1. Aluminium powder is used as reducing agent is thermite process.
2. In thermite process, thermite mixture is taken in a crucible made of fire clay (high temperature resistant). A mixture of magnesium powder and barium peroxide or potassium chlorate is taken over the thermite mixture which is then ignited with a burning magnesium ribbon. The mixture of magnesium powder and potassium chlorate or barium peroxide is called ignition mixture.

Question 22. State three advantages of thermite process.

Answer:

Three advantages of thermite process:

1. Metal extraction by thermite process doesn’t require large machineries. Metals can be extracted in small scale by this method for different purposes.

2. Broken parts of large machineries, rail lines, tram lines, ships can be repaired by thermite process. But, it .is not required to transport the damaged parts to the factories.

3. A huge quantity of Al₂O₃ is produced as a byproduct. This can be used for the preparation of emery powder used in metal polishing and manufacture of bricks used in the inner layer of furnace.

Question 23. Why are the metals occupying lower positions in the metal activity series often found in nature in their native state?

Answer: The metals occupying lower position in the metal activity series (Hg, Ag, Au) have very little chemical reactivity. Hence, they are not easily affected by atmospheric oxygen, water vapour, CO₂ etc., and thus exist in nature in their native state.

Question 24.
1. What happens when Al reacts with cone. NaOH solution?
2. What happens when steam is passed over red hot iron?Write down with equation.

Answer:
1. When Al reacts with cone. NaOH solution, sodium aluminate and hydrogen gas are formed.

\(2 \mathrm{Al}+2 \mathrm{NaOH}+2 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaAlO}_2+3 \mathrm{H}_2 \uparrow\)

 

2. When steam is passed over red hot iron, ferrosoferric oxide and hydrogen gas are formed.

\(3 \mathrm{Fe}+4 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Fe}_3 \mathrm{O}_4+4 \mathrm{H}_2 \uparrow\)

 

Question 25. Write down the reaction occurs at cathode when an aqueous solution of MSO₄ (M = Metal) is electrolysed. State with reason whether the reaction is oxidation or reduction.

Answer: M²⁺ and H⁺ ions are present as cations in aqueous solution of MSO₄ due to following ionic dissocation:

\(\begin{aligned}
\mathrm{MSO}_4 & \rightleftharpoons \mathrm{M}^{2+}+\mathrm{SO}_4^{2-} \\
\mathrm{H}_2 \mathrm{O} & \rightleftharpoons \mathrm{H}^{+}+\mathrm{OH}^{-}
\end{aligned}\)

 

Therefore, the probable reactions at cathode:

\(\mathrm{M}^{2+}+2 e \rightarrow \mathrm{M} ; \mathrm{H}^{+}+e \rightarrow \mathrm{H} ; \mathrm{H}+\mathrm{H} \rightarrow \mathrm{H}_2 \uparrow\)

 

M²⁺ or H⁺ ion accepts electron to become electrically neutral at cathode. Hence reduction reaction takes pace at cathode.

Metallurgy Topic B Principles Of Metal Extraction And Oxidation-Reduction Very Short Answer Type Choose The Correct Answer

Question 1. During extraction of aluminium, alumina is reduced by

1. H₂
2. Carbon
3. H₂S
4. Electrolysis

Answer: 4. Electrolysis

Question 2. During extraction of zinc, ZnO is reduced by

1. H₂
2. Carbon powder
3. H₂S
4. Electrolysis

Answer: 2. Carbon powder

Question 3. In thermite mixture, the ratio of Fe203 and Al powder is

1. 1:2
2. 2:1
3. 1:3
4. 3:1

Answer: 4. 3:1

Question 4. In thermite process, the substances present apart from the thermite mixture are

1. Fe, Cr
2. ZnO, Mg
3. BaO₂, Mn
4. BaO₂, Mg

Answer: 4. BaO₂, Mg

Question 5. Which of the following metals react with boiling water to evolve H₂ but does not do so with cold water?

1. Ca
2. K
3. Al
4. Na

Answer: 3. Al

Question 6. Which of the following metals is placed below Pb and above Hg in the metal activity series?

1. Sn
2. Ag
3. Cu
4. Au

Answer: 3. Cu

Question 7. Which of the following reactions is feasible?

1. \(\mathrm{Zn}+\mathrm{FeSO}_4 \rightarrow\)
2. \(\mathrm{MgSO}_4+\mathrm{Fe} \rightarrow\)
3. \(\mathrm{CuSO}_4+\mathrm{Ag} \rightarrow\)
4. \(\mathrm{ZnSO}_4+\mathrm{Pb} \rightarrow\)

Answer: 1. \(\mathrm{Zn}+\mathrm{FeSO}_4 \rightarrow\)

Question 8. Which of the following metals can be extracted by thermite process?

1. Fe
2. Cu
3. Zn
4. Al

Answer: 1. Fe

Question 9. In thermite process, the metal used as the reducing agent is

1. Al
2. Ni
3. Zn
4. Fe

Answer: 1. Al

Question 10. Metals placed at the top of the metal activity series are usually extracted by

1. Carbon reduction method
2. Reduction by H₂
3. Self-reduction
4. Electrolytic reduction

Answer: 4. Electrolytic reduction

Question 11. Metals placed at the middle region of the metal activity series are usually extracted by

1. Carbon reduction method
2. Reduction by H₂
3. Self-reduction
4. Electrolytic reduction

Answer: 1. Carbon reduction method

Question 12. Metals which can exist in free state in nature are

1. Placed at the top of the metal activity series
2. Placed at the middle of the metal activity series
3. Placed at the bottom of the metal activity series
4. Not included in the metal activity series

Answer: 3. Placed at the bottom of the metal activity series

Question 13. Which of the following orders correctly represents the reactivity of metals?

1. Pb < Fe < Mg
2. Mg > Ca > Zn
3. Ag < Zn < Pb
4. Al > Cu > Fe

Answer: 1. Pb < Fe < Mg

Question 14. Which of the following metal pairs reacts with both acids and alkalies to produce hydrogen gas?

1. Cu, Zn
2. Na, Cu
3. Pb, Zn
4. Al, Zn

Answer: 4. Al, Zn

Question 15. Na cannot be extracted from its oxide by carbon reduction process because

1. Oxide of Na is unstable
2. Na does not exist in its oxide form
3. Oxide of Na is more stable
4. Oxide of Na is volatile

Wbbse Class 10 Metallurgy Of Iron

Answer: 3. Oxide of Na is more stable

Question 16. Metals placed at the top of the metal activity series are

1. Strong reducing agents
2. Weak reducing agents
3. Strong oxidising agents
4. Weak oxidising agents

Answer: 1. Strong reducing agents

Question 17. In the metal activity series, the only non-metal present along with the metals is

1. Carbon
2. Hydrogen
3. Chlorine
4. Iodine

Answer: 2. Hydrogen

Question 18. Up Thermite mixture is

1. Fe₂O₃+ Al
2. Fe₂O₃ + Cu
3. FeO + Al
4. FeO + Cu

Answer: 1. Fe₂O₃+ Al

Question 19. In which of the following change incolouration can be observed when an iron nail is immersed in it

1. ZnSO₄
2. Al(SO₄)
3. FeSO₄
4. CuSO₄

Answer: 4. CuSO₄

Question 20. Which of the following metals does not react with boiling water, but forms H₂ in reaction with steam?

1. Mg
2. Zn
3. Fe
4. Al

Answer: 3. Fe

Question 21. Which of the following metals forms H2 when boiled with strong alkali?

1. Fe
2. Al
3. Cu
4. Mg

Answer: 2. Al

Wbbse Class 10 Metallurgy Of Iron

Question 22.Which of the following is used as reductant in the carbon reduction process of iron extraction?

1. Al
2. CO
3. CO₂
4. CO₃^2-

Answer: 2. CO

Question 23. In which of the following containers ferrous sulphate solution cannot be kept?

1. Copper container
2. Aluminium container
3. Silver container
4. None of the above

Answer: 2. Aluminium container

Question 24. The most reactive metal is

1. Fe
2. Ag
3. K
4. Cu

Answer: 3. K

Question 25. Which of the following metals reacts with water at normal temperature?

1. Na
2. Cu
3. Fe
4. Zn

Answer: 1. Na

Question 26. Which of the following metals cannot be extracted by electrolytic method?

1. Na
2. Zn
3. Al
4. Ca

Answer: 2. Zn

Question 27. Which of’the following can be extracted by carbon reduction method?

1. Al
2. Mg
3. Zn
4. Mn

Answer: 3. Zn

Question 28. The process of metal extraction by another metal is

1. Self-reduction
2. Electrolytic reduction
3. Thermite process
4. All of the above

Answer: 3. Thermite process

Wbbse Class 10 Metallurgy Of Iron

Question 29. The process of extraction of metal from ore is

1. Oxidation
2. Reduction
3. Redox
4. None of the above

Answer: 2. Reduction

Question 30. The oxidising agent in the thermite process is

1. Al
2. Mg-tape
3. Fe₂O₃
4. KClO₃

Answer: 3. Fe₂O₃

Metallurgy Topic B Principles Of Metal Extraction And Oxidation-Reduction Answer In Brief

Question 1. Give an example of a reduction process where an anion accepts an electron.
Answer: \(\mathrm{MnO}_4^{-}+e \rightarrow \mathrm{MnO}_4^{2-}\)

Wbbse Class 10 Metallurgy Of Iron

In this reaction an anion accepts an electron and gets reduced.

Question 2. \(\mathrm{Cu}^{2+}+\mathrm{Zn} \rightarrow \mathrm{Cu}+\mathrm{Zn}^{2+}\)—

Identify the oxidant and reductant in the given reaction.

Answer: In the given reaction, Zn acts as the reductant while Cu²⁺ acts as the oxidant.

Question 3. Name some metals other than iron that can be extracted by thermite process.
Answer: Some metals other than iron that can be extracted from their oxides by thermite process are chromium (Cr), molybdenum (Mo), titanium (Ti), manganese (Mn) etc.

Common Misconceptions About Metallurgy

Question 4. Why is aluminium used in thermite process?
Answer: At high temperatures, aluminium exhibits strong reducing power, i.e., it has a strong affinity towards oxygen. For this reason, aluminium is used in thermite process.

Question 5. Name the element beiow which copper is placed in the metal activity series.
Answer: The element below which copper is placed in the metal activity series is hydrogen.

Question 6. Arrange Pb, Ca, Cu, Zn, Mg in increasing order of their reactivity.
Answer: Cu < Pb < Zn < Mg < Ca .

Question 7. Which metals are extracted , by carbon reduction method?
Answer: Metals which are placed in the middle region of the metal activity series are extracted by carbon reduction method.

Question 8. Arrange Na, Al, Fe, Pb in increasing order of their reducing power.
Answer: The increasing order of reducing power of the given elements is— Pb < Fe < Al < Nai.

Wbbse Class 10 Metallurgy Of Iron

Question 9. Between aluminium and tin, which one occupies a higher position in the metal activity series?
Answer: Aluminium occupies a higher position than tin in the metal activity series.

Question 10. Name a metal which reacts only with acids to produce hydrogen (H₂).
Answer: Tin (Sn) reacts only with acids to produce hydrogen (H₂).

Question 11. Give the equation of the reaction in which Mn+ ion is converted into metal M at the cathode during electrolysis of a fused salt containing Mn+ ion.
Answer: The equation is: Mⁿ⁺ + ne → M.

Question 12. What happens during the electrolytic reduction of fused NaCI?
Answer: During the electrolytic reduction of fused NaCI, Na is deposited at the cathode and CI₂ gas is liberated at the anode.

Question 13. Give example of a metal which can form H2 in reaction with steam.
Answer: Iron (Fe) forms H₂ in reaction with steam.

Question 14. Which one among Fe, Cu, Zn and Al does not form H₂ in reaction with dil H₂SO₄?
Answer: Cu is present in a lower position than H in metal activity series and thus does not form H₂ in reaction with dil. H₂SO_4.

Question 15. Write down the principle of Goldschmidt’s thermite process.
Answer: The fundamental principle of Goldschmidt’s thermite process is the reduction of the oxide of a less electropositive metal by another metal with higher electropositivity.

Question 16. Which substance is used as oxidant in thermite process?
Answer: Oxides of Fe, Cr, Mn etc., are used as oxidant in thermite process.

Question 17. Write down the reaction temperature of thermite process.
Answer: 2000°C.

Question 18. Write down an use of thermite process.
Answer: Thermite process is used in welding broken parts of heavy machineries, rail lines, tram lines, ships etc.

Question 19. Write down the equation of extraction of iron from red haematite by thermite process.
Answer:

\(\mathrm{Fe}_2 \mathrm{O}_3+2 \mathrm{Al} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{Fe}+\mathrm{Al}_2 \mathrm{O}_3\)

Wbbse Class 10 Metallurgy Of Iron

Question 20. Give example of two metals which cannot be extracted by carbon reduction process.
Answer: Sodium (Na) and aluminium (Al).

Question 21. Write down the general equation for carbon reduction process.
Answer:

\(\mathrm{MO}+\mathrm{C} \stackrel{\Delta}{\longrightarrow} \mathrm{M}+\mathrm{CO}(\mathrm{M}=\text { metal) }\)

Question 22. What is the name of the gas formed along with metals in carbon reduction process?
Answer: Carbon monoxide (CO).

Question 23. Which process of metal extraction is applied for the extraction of K, Ca, Na etc.?
Answer: Electrolytic process.

Question 24. In which electrode metal atoms are deposited in the electrolytic reduction method of metal extraction?
Answer: Cathode.

Question 25. Write down the name of two metals that can be extracted by electrolytic reduction method.
Answer: Aluminium (Al) and calcium (Ca).

Metallurgy Topic B Principles Of Metal Extraction And Oxidation-Reduction Fill In The Blanks

Question 1. During electrolysis, metal cations move towards the cathode and get ______ by ______ accepting .
Answer: Reduced,electrons

Question 2. A metal oxide gets ______ removed from it.
Answer: Reduced

Question 3. On moving down the metal activity series, reducing power of the metals gradually _______
Answer: Decreases

Wbbse Class 10 Metallurgy Of Iron

Question 4. The extraction of a metal from the corresponding metal compound is always a ______ process.
Answer: Reduction

Question 5. The metal occupying the topmost position in the metal activity series is ______
Answer: Potassium

Question 6. _____ is also known as zinc white.
Answer: ZnO

Question 7. The constituents of thermite mixture are ______ and ______
Answer: Fe₂O₃, Al-powder

Question 8. Less reactive metals are found in nature in their ______ state.
Answer: Free

Question 9. In aqueous solution, a more reactive metal can ______ or _____ a less reactive metal from its salt.
Answer: Precipitate, reduce

Question 10. Metals placed at the top of the metal activity series have ______ affinity towards oxygen.
Answer: High

Question 11. In the metal activity series, Zn is placed_____ CU.
Answer: Above

Wbbse Class 10 Metallurgy Of Iron

Question 12. Among Fe, Cu, Zn and Al, ______ occupies the highest position in the metal activity series.
Answer: Al

Question 13. _____ dust is used as reductant in thermite process.
Answer: Aluminium

Question 14. Generally ______is used as reductant in carbon reduction process.
Answer: Coke

Question 15. Example of a metal that can be extracted by carbon reduction process is _____
Answer: Zinc

Question 16. The metal occupying the last position in the metal activity series is ______
Answer: Gold

Question 17. In the reaction, 2Fe³⁺ + Sn²⁺ → 2Fe²⁺ + Sn⁴⁺, Fe³⁺ acts as the ______ while Sn²⁺ acts as the ______
Answer: Oxidant, reductant

Metallurgy Topic B Principles Of Metal Extraction And Oxidation-Reduction State Whether True Or False

Question 1. Fe can be extracted by thermite process.
Answer: True

Question 2. Metals placed at the top of the metal activity series are extracted by carbon reduction procedure.
Answer: False

Question 3. Metals placed at the top of the metal activity series are strong oxidising agent.
Answer: False

Question 4. Extraction of metal from ore is mainly oxidation.
Answer: False

Question 5. Thermite reaction is endothermic.
Answer: False

Question 6. Carbon is used as reductant in thermite process.
Answer: False

Question 7. Zinc cannot be extracted by carbon reduction process.
Answer: False

Question 8. Metals are obtained at cathode in electrolytic reduction process.
Answer: True

Metallurgy Topic C Corrosion Of Metals Synopsis

1. If an iron object is left in moist air for a long time, then a reddish-brown layer of hydrated ferric oxide (Fe₂O₃ -xH₂O) is formed over the object at ordinary temperature which is commonly known as rust.
2. Rusting of iron is accelerated in the presence of ions like CI^–, SO₄^2- Thus, rusting becomes a major problem in case of ships and underground pipelines.
3. Some practical methods of preventing rusting of iron are—painting the surface of the iron object, coating the surface of the object with varnish, galvanisation or attaching a magnesium block to the iron object (sacrificial protection). Consequently, rusting of iron is prevented.
4. When an aluminium article comes in contact with moist air, a thin non-conducting layer of Al₂O₃ is formed over it, which protects it from further corrosion.
5. If copper objects are left in moist air for a long time, a green layer (basic copper carbonate) is formed over those objects.
6. Food items or fruits containing acids should not be stored or processed in containers made up of Al, Zn or Cu as it may lead to toxicity of food.

Metallurgy Topic C Corrosion Of Metals Short And Long Answer Type Questions

Question 1. What is corrosion of metal?

Answer:

corrosion of metal:

When a piece of metal is kept in open air for a long time, the metal chemically reacts with atmospheric oxygen, CO₂  , water vapour etc., and is converted into other substances. As a result the metal piece erodes. This natural phenomenon is known as corrosion of metal.

Question 2. Why impure metals undergo quicker weathering as compared to the pure metals?

Answer: When a piece of impure metal is kept in open air, the impurities present in the metal acts as tiny electrochemical cells on the surface of the metal. Hence, it can be affected readily by atmospheric oxygen, water vapour etc. Pure metal generally does not form such cells and thus they are not weathered easily.

Question 3. What do you mean by rusting of iron? Why are metal articles corroded due to rusting?

Answer:

Rusting of iron:

1. When iron or iron objects are kept in moist air for a few days, a reddish brown layer of hydrated ferric oxide (Fe₂O₃-xH₂O) is formed over the objects. This reddish brown layer is called rust and the process is called rusting.
2. The volume of rust is generally greater than the volume of pure iron. Hence, after the formation of rust, the surface becomes flaky and comes out of the metal easily. Therefore, the objects undergo corrosion.

Question 4. Explain the mechanism of rusting.

Answer:

Mechanism of rusting

Rusting of iron is basically an electrochemical reaction. Due to the presence of impurities and rough surface, the oxidation of iron atoms do not take place uniformly. Some parts of iron gets readily oxidised than some other parts.

The part where oxidation takes place easily is called the anode region while the part where oxidation does not take place easily is called the cathode region. At anode region, Fe-atoms give up electrons and gets oxidised to Fe²⁺ ions which dissolve in water.

The released electrons move to the cathode region. At cathode region, O₂ dissolved in water accept these electrons and is reduced to water. The reduction takes place in presence of H⁺ ions that are obtained from the dissociation of carbonic add (H₂CO₃).

Word Problems on Metal Extraction and Refining

Anode reaction: \(2 \mathrm{Fe} \rightarrow 2 \mathrm{Fe}^{2+}+4 e\)

Cathode reaction: \(\begin{aligned}
& 4 \mathrm{H}^{+}+4 e \rightarrow 4 \mathrm{H} \\
& 4 \mathrm{H}+\mathrm{O}_2 \rightarrow 2 \mathrm{H}_2 \mathrm{O}
\end{aligned}\)

Net reaction: \(2 \mathrm{Fe}+\mathrm{O}_2+4 \mathrm{H}^{+} \rightarrow 2 \mathrm{Fe}^{2+}+2 \mathrm{H}_2 \mathrm{O}\)

Fe²⁺ ions produced at anode are further oxidised by aerial oxygen to form hydrated ferric oxide or rust (Fe₂O₃-xH₂O).

\(\begin{aligned}
& 4 \mathrm{Fe}^{2+}+\mathrm{O}_2+4 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{Fe}_2 \mathrm{O}_3+8 \mathrm{H}^{+} \\
& \mathrm{Fe}_2 \mathrm{O}_3+x \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Fe}_2 \mathrm{O}_3 \cdot x \mathrm{H}_2 \mathrm{O} \text { (rust) }
\end{aligned}\)

 

Question 5. What are the factors which accelerates the process of rusting?

Answer:

The process of rusting is accelerated by the following factors—

1. Presence of less electropositive metals in iron as impurity.
2. The presence of gases like CO₂, SO₂, SO₃, NO, NO₂ etc.
3. Presence of chloride (CI^–) or sulphate (SO₄^2- ) ions in water.

Question 6. Discuss the harmful effects of rusting.

Answer:

The harmful effects of rusting

1. Rusting affects the metallic lustre of iron.
2. Ironisusedtopreparesubstancesforhousehold works, transportation, agricultural and defence instruments. These substances corrode due to rusting causing huge economic losses.
3. Flouses, bridges etc. contain iron pillars. Similarly bodies of ships are made of iron. Rusting, makes them weak and brittle, which may lead to accidents.

Question 7. Why is rusting called “slow combustion’?

Answer: In the presence of aerial oxygen and water vapour, iron is oxidised to hydrated ferric oxide (Fe₂O₃ xH₂O) or rust. During this process, small amount of heat is also produced. Hence, it is sometimes called a ‘slow combustion’.

Question 8. Give some methods to prevent rusting of iron.

Answer:

Some methods to prevent rusting of iron

1. The iron articles can be protected from rusting by coating their surfaces with varnishes, paints or coal tar.
2. Rusting can be prevented by electroplating iron with zinc, tin or chromium.
3. When steam is passed over red hot iron, a thin layer of ferrosoferric oxide (Fe₃O₄) is formed on the surface of iron which protects it from rusting.
4. The underground oil pipelines through water, made of iron are protected by using Mg- blocks.

Question 9. Why do the oil or water pipelines through oceans and seas tend to form rust readily? How are they protected from rusting?

Answer:
1. Ocean and sea water contains dissolved chloride (CI^– ) and sulphate (SO₄^2-) ions. These ions facilitate the process of rusting. Hence, oil or water pipelines through oceans and seas tend to form rust readily.
2. To protect the underground or underwater pipelines from rusting, a block of more electropositive metal (like Mg) is connected to the pipe through an insultated wire. In this case, the iron pipes act as cathode, the magnesium block as anode and water as electrolyte. Magnesium being more reactive than iron is readily oxidised and hence prevents iron from rusting. The Mg block needs to be replaced after sometime as it corrodes gradually.

 

 

Question 10. Several magnesium blocks are attached to the bottom of ships. Why?

Answer:

Several magnesium blocks are attached to the bottom of ships.

The salty water of seas and oceans accelerates the process of rusting. The magnesium blocks attached to the bottom of the ships protect the iron parts of ships from rusting. Here, the ship acts as an electrochemical cell.

Mg is placed above iron in the metal activity series and hence, Mg acts as anode while iron acts as cathode. The salty water of ocean acts as an electrolytic solution. As oxidation takes place at anode, Mg is preferably oxidised to Mg²⁺ ions.

Thus iron remains unaffected as long as Mg blocks are present. New blocks replaces the already attached blocks that gets corroded.

Question 11. What do you mean by galvanisation?

Answer:

Galvanisation:

To protect iron from rusting and corrosion, sometimes a zinc coating is applied over iron objects mainly by electrolytic method. This is known as galvanisation. Iron coated with zinc is called galvanised iron.

Question 12. Why is zinc used in galvanisation to prevent rusting?

Answer: In the metal activity series zinc is placed above iron. Hence, zinc is more electropositive than iron and it is more easily oxidised than iron. So, when iron is coated with zinc, zinc is more readily affected by oxygen and water vapour. This protects iron from being oxidised. Thus, rusting is prevented.

Question 13. Zinc is more electropositive than iron, so it should be corroded more readily than iron. But, this doesn’t happen. Instead, zinc is coated over iron to prevent rusting. How will you explain this?

Answer: When zinc is exposed to air it is affected by oxygen, CO₂ and water vapour present in the air to form a layer of basic [Zn(OH)₂ • ZnCO₃].

This layer shields zinc from atmospheric air and hence further corrosion is prevented. This is why zinc is used to protect iron from rusting.

Question 14. Wilt it be justified to coat an iron cauldron/ used for cooking, with zinc to protect the cauldron from rusting?

Answer: The melting point of zinc is 420°C. while that of iron is 1525°C, i.e., zinc has a much lower melting point than iron. At about 250°C, zinc becomes brittle and the layer may break on application of higher temperature. Hence, it is not suitable to coat an iron cauldron, used for cooking, with zinc to protect the cauldron from rusting.

Question 15. To protect iron from rusting which one between zinc-plating and tin-plating is more effective and why?

Answer: When a crack on the surface of zinc-plated iron exposes the metallic iron, the metallic iron remains unaffected by the action of moist air and does not corrode. This is because, zinc is more reactive than iron(zinc is at higher position than iron in metal activity series) and hence zinc is affected by moist air more readily than iron.

On the other hand, any crack on the surface of tinplated iron which exposes iron makes the iron part vulnerable to rusting. This is because iron is more reactive than tin and hence iron is affected by moist air more readily than tin.This is why zinc-plating is more effective in preventing rust than tin-plating.

Question 16. Explain why tin-plated utensils are use- instead of zinc plated utensils to store food.

Answer: Zinc is more effective in preventing rusting and corrosion. Yet, tin-plated containers are more widely used to store food than zinc-plated containers because zinc may react with some acids present in food to produce toxic substances which may cause food poisoning. Tin does not produce such toxic substances. Hence, it is safer to use tinplated containers to store food.

Question 17. Why is aluminium protecting metal?

Answer:
1. When metallic aluminium is kept in moist air, it reacts oxygen and water vapour to form a nonconducting thin layer of aluminium oxide (Al₂O₃) over it’s surface. As a result, the metallic lustre is lost. But, the layer formed is in-soluble in water and protects the metal from further oxidation. Hence, corrosion of the metal is prevented. This is why aluminium is called a ‘self- protecting’ metal.

Question 18. Copper objects turn green when kept in air for a long time. Explain.

Answer:

Copper objects turn green when kept in air for a long time.

When exposed to moist air for a long period of time, copper is oxidised by aerial oxygen to copper oxide (CuO) which deposits on the surface of the object. Due to presence of H₂S in the air of industrial area, black layer of copper sulphide (CuS) is formed on the surface of the article. This layer is further oxidised to form green coloured basic copper sulphate [CuSO₄– 3Cu(OH)₂ ].

Sometimes, copper is also oxidised by O₂, CO₂ and water vapour to green coloured basic copper carbonate [CuCO₃ • Cu(OH)₂]. Due to the formation of these compounds, the object turns green.

Visual Representation of Metallurgical Processes

 

Question 19. Copper vessels are sometimes cleaned with lemon or tamarind. What is the possible reason for this?

Answer:

Copper vessels are sometimes cleaned with lemon or tamarind

Copper vessels are oxidised by O₂, CO₂   and water vapour to form a thin layer of green-coloured basic copper carbonate [CuCO₃ • Cu(OH)₂] . Lemon or tamarind contains organic acids. These organic acids react with basic copper carbonate and remove the green patches. Hence; the green patch or stain gets removed from the vessels.

Question 20. Copper utensils which are not used fora long time should be used only after thorough cleaning—explain.

Answer:

Copper utensils which are not used fora long time should be used only after thorough cleaning

Green coating of basic copper carbonate is formed on copper utensils which are not used for a long time as a result of reaction of copper with atmospheric oxygen, carbon dioxide and water vapour, Basic copper carbonate is toxic in nature.

It causes toxicity if it is consumed along with food. Moreover, several micro-organisms which can cause diseases may be present on those utensils. That is why these copper utensils should be used only after thorough cleaning.

Question 21. Gold ornaments are often covered with green patches on their surfaces. Why?

Answer:

Gold ornaments are often covered with green patches on their surfaces

To increase the strength of gold for making ornaments, copper is added as an impurity. In moist air, this copper is slowly oxidised over a long period of time to form green coloured basic copper sulphate [CuSO_{4 •} Cu(OH)₂] or basic copper carbonate [CuCO₃ • Cu(OH)₂]. The green patches on the gold ornaments appears due to the formation of these compounds.

Question 22. Explain why it is harmful to eat pickles or chutneys kept in an aluminium foil.

Answer: Vinegar is generally used as an ingredient for making pickles or chutneys. Vinegar is nothing but an aqueous solution of acetic acid (CH₃COOH). Thus, it reacts with aluminium to form poisonous aluminium salt. Hence, it is harmful to eat pickles or chutneys kept in aluminium foil as it may cause food poisoning.

Question 23. Food or fruits haying sour taste should not be stored in containers made of aluminium, zinc or copper. Why?

Answer:

Food or fruits haying sour taste should not be stored in containers made of aluminium, zinc or copper.

Food or fruits having sour taste contains organic acids. These organic acids reacts with aluminium or zinc to form water soluble salts. Similarly, copper may also form water soluble salts with organic acids in the presence of oxygen. Some of the produced salts are toxic and may cause food poisoning. Hence, it is advisable not to store food or fruits having sour taste in containers made of aluminium, zinc or copper.

Metallurgy Topic C Corrosion Of Metals Very Short Answer Type Question Choose The Correct Answer

Question 1. The chemical formula of rust is

1. FeO•xH₂O
2. Fe₂O₄
3. FeO₃
4. Fe₂O₃ •xH₂O

Answer: 4. Fe₂O₃ •xH₂O

Question 2. Presence of which of the following ions accelerates the process of rusting?

1. Na⁺
2. Ca²⁺
   
3. CI^– 
4. O^2-

Answer: 2. Ca²⁺

Question 3. Which of the following is used to protect the iron parts of ships from rusting?

1. Copper blocks
2. Aluminium blocks
3. Zinc blocks
4. Magnesium blocks

Answer: 4. Magnesium blocks

Question 4. Which of the following methods does not prevent rusting?

1. Painting the surface
2. Galvanisation
3. Using a Mg-block
4. Immersing in MgCl₂ solution

Answer: 4. Immersing in MgCl₂ solution

Question 5. During rusting, presence of which of the following ions in water causes the reduction of dissolved O₂ ?

1. Fe²⁺ 
2. Fe³⁺ 
3. H⁺ 
4. Self-reduction occurs in this case

Answer: 3. H⁺ 

Question 6. To prevent rusting, Mg-block is attached to iron pipes because

1. Mg is more electropositive than Fe
2. Mg has a greater tendency to get oxidised than Fe
3. Both 1 and 2
4. None of these

Answer: 3. Both 1 and 2

Question 7. Galvanised iron is actually

1. Zn-coated iron
2. Sn-coated iron
3. Ni-coated iron
4. Cr-coated iron

Answer: 1. Zn-coated iron

Question 8. Green layer formed over copper and most of its alloys when exposed to moist air, is of

1. Basic copper nitrate
2. Acidic copper hydroxide
3. Basic copper carbonate
4. Acidic copper sulphate

Answer: 3. Basic copper carbonate

Question 9. Which of the following metals can protect itself from corrosion?

1. Al
2. Fe
3. Na
4. Cu

Answer: 1. Al

Physical Science Class 10 West Bengal Board

Question 10. The white layer formed over metallic aluminium in presence of moist air is of

1. AlCl₃
2. Al (OH)₃
3. Al₂O₃
4. AIN

Answer: 3. Al₂O₃

Question 11. Which metal protects itself by forming a coat of oxide?

1. Cu
2. Al
3. Fe
4. Zn

Answer: 2. Al

Question 12. Necessary component required for rust formation is

1. N₂ ,O₂
2. N₂ ,H₂ 
3. O₂,H₂O
4. CO₂, H₂O

Answer: 3. O₂,H₂O

Question 13. Which of the following is formed by the reaction of Al or Zn with organic acidic substances?

1. Soluble metallic salts
2. Insoluble metallic salts
3. Addition compound
4. Metallic hydroxides

Answer: 1. Soluble metallic salts

Physical Science Class 10 West Bengal Board

Question 14. Which of the following metals is used for galvanisation?

1. Fe
2. Ca
3. Zn
4. Mg

Answer: 3. Zn

Question 15. Rusting is a

1. Oxidation process
2. Reduction process
3. Redox process
4. Neutralisation reaction

Answer: 3. Redox process

Question 16. Rapid rusting of iron occurs in presence of Cl- because

1. Dissociation of water molecule increases
2. Dissociation of water molecule decreases
3. Chlorine gas reacts with iron
4. None of the above

Answer: 1. Dissociation of water molecule increases

Metallurgy Topic C Corrosion Of Metals Answer In Brief

Question 1. Apart from aerial oxygen, which other component of the atmosphere is responsible for rusting of iron?
Answer: Apart from aerial oxygen, water vapour is responsible for rusting of iron.

Question 2. Which type of impurity facilitates the rusting of iron?
Answer: Presence of less electropositive metals in iron as impurities facilitates rusting.

Question 3. Name an electrochemical process.
Answer: Rusting of iron is an electrochemical process.

Question 4. Write the reactions that occur at the anode and cathode during rusting of iron.
Answer:
Anode reaction: \(2 \mathrm{Fe} \rightarrow 2 \mathrm{Fe}^{2+}+4 e\)

Cathode reaction: \(\mathrm{O}_2+4 \mathrm{H}^{+}+4 e \rightarrow 2 \mathrm{H}_2 \mathrm{O}\)

Question 5. Name a metal apart from zinc that can be used as a coating over iron to protect it from rusting?
Answer: Apart from zinc, tin can be used as a coating over iron to protect it from rusting.

Physical Science Class 10 West Bengal Board

Question 6. The presence of chloride ions facilitate rusting of iron. Mention one practical disadvantage of it.
Answer: Underwater pipelines made of iron are easily corroded by rusting due to the presence of CI^– ions in sea water.

Question 7. How can you protect iron from rusting?
Answer: If steam is passed over red hot iron, a thin layer of ferrosoferric oxide (Fe₃O₄) is formed over iron, which protects it from rusting.

Question 8. Write the composition of the green coloured layer formed on copper and most copper alloys when exposed to moist air for a long time.
Answer: Basic copper carbonate [CuCO₃-Cu(OH)₂].

Physical Science Class 10 West Bengal Board

Question 9. What are the necessary conditions required for rusting?
Answer: The process of rusting requires
1. Presence of atmospheric oxygen,
2. Presence of water vapour.

Question 10. Why does rusting not occur in pure iron?
Answer: Many electrochemical cells are formed on iron during rusting. In absence of impurities these cells cannot be formed and hence rust is not formed on pure iron.

Question 11. Presence of which ion accelerates rusting?
Answer: Presence of CI^– ion accelerates rusting.

Question 12. Why does rusting accelerate in presence of CO₂?
Answer: CO₂ forms carbonic acid by dissolving in water which increases the rate of dissociation of water. Hence rusting is accelerated.

Physical Science Class 10 West Bengal Board

Question 13. Name a process which protects iron from rusting.
Answer: Galvanisation.

Question 14. Which metal is used in galvanisation?
Answer: Zinc (Zn).

Question 15. What is “galvanised iron”?
Answer: Iron coated with metallic zinc is termed as ‘galvanised iron’ or G.l.

Question 16. Write down the advantage of galvanisation.
Answer: Galvanisation protects iron from rusting and corrosion.

Question 17. Which metal is used in cathodic protection of iron?
Answer: Magnesium is used in cathodic protection of iron.

Physical Science Class 10 West Bengal Board

Question 18. What is used as a suicidal electrode to prevent rust on a ship?
Answer: Magnesium block.

Question 19. What is passive iron?
Answer: A coating of iron oxide is formed over iron when it comes in contact with cone, nitric acid. This makes iron chemically inert and this type of iron is called passive iron.

Question 20. Which metal is called “self protecting metal”?
Answer: Aluminium is called ‘self protecting metal’.

Question 21. Which compounds are responsible for the formation of green coating on copper containers?
Answer: Basic copper carbonate [CuCO₃ • Cu(OH)₂] and basic copper sulphate [Cu SO₄ • 3Cu(OH)₂] .

Question 22. What is patina?
Answer: A green film of basic copper carbonate [Cu SO₄  • Cu(OH)₂] formed by the reaction of metallic copper with O₂, CO₂ and water vapour on the surface of copper made substances is called patina.

Question 23. Write down the formula of basic zinc carbonate.
Answer: ZnCO₃ • 3Zn(OH)₂ .

Physical Science Class 10 West Bengal Board

Metallurgy Topic C Corrosion Of Metals Fill In The Blanks

Question 1. During rusting/oxygen dissolved in water gets reduced to form ______
Answer: H₂O

Question 2. Presence of ______ substances prevents rusting of iron.
Answer: Alkaline

Question 3. Rusting can be prevented if iron is kept in contact with _____ electropositive metals than iron.
Answer: More

Question 4. A thin non-conducting layer of _____ over Al prevents the metal from getting attacked by atmospheric 02 and moisture.
Answer: Al₂O₃

Question 5. Acidic food or fruits should not be kept in containers made of _____ or _____
Answer: Al, Zn

Physical Science Class 10 West Bengal Board

Question 6. Different weather conditions causes metallic objects to lose their ______
Answer: Lustre

Question 7. Rust do not occur in ______ iron.
Answer: Pure

Question 8. Rate of rusting _______ with increase in temperature.
Answer: Increase

Question 9. Process of coating ______ on iron substances is called galvanisation.
Answer: Zinc

Question 10. Mg-block attached with iron pipes for oil transportation, acts as _____
Answer: Anode

Question 11. The fine coating formed on Al metal in presence of moist air is of ______
Answer: Al₂O₃

Question 12. __________ coloured patches occur on copper containers if they are kept in opne air.
Answer: Green

Question 13. Due to formation of basic _____ in presence of moist air,zinc becomes faded.
Answer: Zinc carbonate

Question 14. Mg-blocks attached to underground pipes carrying oil act as the ______
Answer: Anode

Metallurgy Topic C Corrosion Of Metals State Whether True Or False

Question 1. Cl ion accelerates the process of rusting.
Answer: True

Question 2. Objects made of copper turn green on prolonged exposure to air due to the formation of basic copper carbonate.
Answer: True

Question 3. It is justified to coat an iron cauldron used for cooking, with zinc to protect the cauldron from rusting.
Answer: False

Question 4. Ni-coated iron is known as galvanised iron.
Answer: False

Physical Science Class 10 West Bengal Board

Question 5. Chemical formula of rust formed on iron is FeO•x H₂O.
Answer: False

Question 6. Rusting occurs in the presence of water only.
Answer: False

Question 7. Pure metals are weathered more readily compared to impure metals.
Answer: False

Question 8. Rusting is a mild combustion.
Answer: True

Question 9. No atmospheric corrosion occurs aluminium if it is kept in open air.
Answer: True

Question 10. Aluminium pot is very useful for storing pickles and sauces.
Answer: False

Physical Science Class 10 West Bengal Board

Question 11. Sour fruits should not be kept cut in zinc coated containers.
Answer: True

Miscellaneous Type Questions Match The Column

Question 1.

Column A	Column B
China clay	1. Ore of Cu
Magnetite	2. Ore of Zn
Calamine	3. Mineral of Al
Malachite	4. Mineral of Fe

 

Answer:
China clay: 3. Mineral of Al
Magnetite: 4. Mineral of Fe
Calamine: 2. Ore of Zn
Malachite: 1. Ore of Cu

Question 2.

Column A	Column B
K	1. Used to protect iron parts of ships from rusting
Zn	2. Reacts with both acid and base to produce H2
Au	3. Strong reducing agent
Mg	4. Obtained in free state in nature

 

Answer:
K: 3. Strong reducing agent
Zn: 2. Reacts with both acid and base to produce H₂
Au: 4. Obtained in free state in nature
Mg: 1. Used to protect iron parts of ships from rusting

Question 3.

Column A	Column B
Ca	1. Reacts with steam in red hot state to produce hydrogen
Pb	2. Reacts with cold water to produce hydrogen
Cu	3. Reacts only with acids to produce hydrogen
Zn	4. Does not produce hydrogen on reaction with acid

 

Answer:
Ca: 2. Reacts with cold water to produce hydrogen
Pb: 3. Reacts only with acids to produce hydrogen
Cu:  4. Does not produce hydrogen on reaction with acid
Zn:  1. Reacts with steam in red hot state to produce hydrogen

WBBSE Solutions for Class 10 Physical Science and Environment

Chapter 7 Atomic Nucleus Topic A Radioactivity Synopsis

WBBSE Class 10 Atomic Nucleus Overview

1. Radioactive elements are those elements whose atoms spontaneously emit a type of special invisible radiation and get converted into atoms of new elements.

2. Radioactivity was discovered by Henri Becquerel in uranium salt in the year 1896.

3. Radioactivity is the property due to which some elements with high atomic mass numbers spontaneously emit a type of special invisible radiation and get converted into atoms of new elements.

4. All the elements with atomic numbers greater than 82 are naturally radioactive.

5. Some non-radioactive elements may be converted into radioactive elements artificially. The radioactivity of these new elements produced artificially is called artificial radioactivity.

6. The phenomenon of spontaneous emission of rays from an unstable nucleus is called
radioactive decay.

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

7. radioactive element or atom that exhibits radioactivity is called a parent atom. The atom that is left behind after the emission of radioactive radiation is called the daughter atom.

8. No radioactive sample can emit all three radiations simultaneously.

Wbbse Class 10 Physical Science Solutions

8. Three types of rays are emitted in radioactivity.

α – ray: It is a stream of positively charged particles.

β – ray: It is a stream of negatively charged particles.

γ – ray: It is an electromagnetic wave.

9. Charge of an or α-particle is twice the charge of a proton, its symbol is \({ }_2^4 \mathrm{He}\), mass is 6.642 x10^-27 kg (or 4.0015 u).

10. Charge of a β-particle is equal to the charge of an electron, i.e., -1.6 x 10^-19 C. Its symbol is \({ }_{-1}^0 \beta,\) mass is 9.1 x 10^-31 kg.

11. If an atomic nucleus undergoes α-decay, the atom is transformed into an atom with a mass number that is reduced by four units and an atomic number that is reduced by two units.
\(
{ }_Z^A X \longrightarrow{ }_{Z-2}^{A-4} Y+{ }_2^4 \mathrm{He}
\)
(parent)  (daughter)

12. If an atomic nucleus undergoes β-decay, the atom is transformed into another atom whose mass number remains unchanged, and the atomic number increases by one unit.
\(
{ }_Z^A p \longrightarrow{ }_{Z+1}^A Q+{ }_{-1}^0 e
\)
(parent) (daughter)

WBBSE Solutions for Class 10 History	WBBSE Solutions for Class 10 Geography and Environment
WBBSE Class 10 History Long Answer Questions	WBBSE Solutions for Class 10 Life Science And Environment
WBBSE Class 10 History Short Answer Questions	WBBSE Solutions for Class 10 Maths
WBBSE Class 10 History Very Short Answer Questions	WBBSE Solutions for Class 10 Physical Science and Environment
WBBSE Class 10 History Multiple Choice Questions

 

Wbbse Class 10 Physical Science Solutions

13. If γ-ray is emitted from a nucleus, the mass number and an atomic number of the atom remain unchanged.

14. Radioactive isotopes are used for the treatment of cancer, leukemia, and diseases of the thyroid. In addition, the radioisotope of carbon ¹⁴C is used for determining the age of a fossil or archaeological object.

Chapter 7 Atomic Nucleus Topic A Radioactivity Short And Long Answer Type Questions

Understanding Protons and Neutrons in the Nucleus

Question 1. What is radioactivity? Which: eSemerit does show radioactivity?
Answer:

Radioactivity:

1. Radioactivity is the property due to which some elements with high atomic mass numbers spontaneously emit a type of special invisible radiation and get converted into atoms of new elements.
2. In Elements in which the ratio of neutrons and protons in the nuclei is more than 1.5, the nuclei are unstable. These elements emit radioactive radiation spontaneously and try to become stable. Only that element shows radioactivity whose mass number is 210 or more than that.

Question 2. What are the characteristics of radioactivity?
Answer:

The characteristics of radioactivity are:

1. Radioactive rays emit spontaneously and ceaselessly from a radioactive element.
2. No effect does occur in the emission of radioactive rays even in the application of heat, pressure, light, electric field, or magnetic field on the radioactive substance.
3. If radioactive elements undergo a chemical change and form other compounds, there is no change in their radioactive nature.
4. Radioactivity of an element is a phenomenon fully associated with its nucleus, there is no connection with its electronic configuration.
5. Structure of the nucleus changes as a result of the emission of radioactive rays. In other words, the numbers of protons and neutrons in the nucleus change, and as a result, a new element is formed.

Question 3. Write down three characteristics of radioactive radiation.
Answer:

Characteristics of radioactive radiation:

1. The radiation has a high penetrating power. For example, gamma rays require a 1 cm thick lead slab to reduce their intensity by 50%.
2. Radioactive rays can ionize a gas.
3. This radiation affects the photographic plates.

Wbbse Class 10 Physical Science Solutions

Question 4. What is artificial radioactivity? Name three artificial radioactive elements.
Answer:

Artificial radioactivity:

1. Some non-radioactive elements may be converted into radioactive elements artificially. The radioactivity of these new elements produced artificially is called artificial radioactivity.
2. Three artificial radioactive elements are

Question 5. Radioactivity of any element is completely a nuclear phenomenon-explain?
Answer:

Radioactivity of any element is completely a nuclear phenomenon:

1. The property of radioactivity of radioactive elements remains unchanged even when they form other compounds after their chemical change. For example, radium chloride, a compound of radioactive radium, is also radioactive.
2. The chemical properties of an element depend on the electronic configuration in its different orbits. As the radioactivity of a radioactive element remains present after chemical changes, so there is no relation between radioactivity and the electronic configuration of the element.
3. Furthermore, an element with new properties is formed as a result of the emission of radioactive rays. This is possible only if there is a change in the structure of the nucleus, i.e., a change in the number of neutrons and protons in the nucleus. This is why it is said that the radioactivity of any element is completely a nuclear phenomenon.

Question 6. Define parent atom and daughter atom. What is the position of a daughter atom in the periodic table when one a -particle is emitted from the nucleus of a radioactive element? What is the position of a daughter atom in the periodic table when one β-particle is emitted from the nucleus of a radioactive element?
Answer:
1. Parent atom of the radioactive element is that atom that undergoes radioactive decay. The atom of the new element which is produced after the emission of the radioactive rays is called the daughter atom.
2. If one α-particle is emitted from the nucleus of a radioactive element, the atomic number of the daughter atom is reduced by two units. So the daughter element moves 2 places to the left in the periodic table compared to the parent atom.
3. If one β-particle is emitted from the nucleus of a radioactive element, the atomic number of the daughter atom is increased by one unit. So the daughter element moves 1 place to the right in the periodic table compared to the parent atom.

Wbbse Class 10 Physical Science Solutions

Question 7. Compare α-ray, β-ray, and γ-ray on the basis of their masses.
Answer:

Comparison among α-ray, β-ray, and γ-ray on the basis of their masses is discussed below:

α-ray	β-ray	γ-ray
The mass of one α-ray-particle is nearly 4 times greater than the mass of a proton. Its mass is 6.642 X 1027     kg.	The mass of one β-ray particle is nearly equal to the mass of an electron or 9.1 x 10-31  kg.	γ-ray is a type of electromagnetic radiation signifying that its mass is zero.

Question 8. Compare α-ray, β-ray, and γ-ray on the basis of their charges.
Answer:

Comparison among α-ray, β-ray, and γ-ray on the basis of their charges discussed below:

α-ray	β-ray	γ-ray
α-ray is a stream of positively charged particles. The nature ofα-ray particle is similar to that of a helium ion (He2+) with 2 units of positive charge. The charge of an a-particle is 3.2 x 10-19 C. It is twice the charge of a proton.	β-ray is a stream of negatively charged particles. The charge of a β-ray particle is equal to the charge of an electron i.e., -1.6 x 10-19 C.	γ-ray is a type of electromagnetic wave with a small wavelength. This is not the stream of any particle. γ-ray is electrically neutral.

Question 9. Compare α-ray, β-ray-ray, and γ-ray on the basis of their penetrating power.
Answer:

Comparison among α-ray, β-ray, and γ-ray on the basis of their penetrating power discussed below:

α-ray	β-ray	γ-ray
α-ray has less penetrating power than β-ray and γ-ray In practice, after progressing a few centimeters through the air, an α-ray particle becomes motionless.	The penetrating power of β-ray is greater than that of α-ray but less than that of γ-ray. An aluminum foil of 5 mm thickness can stop β-ray.	The penetrating power of γ-ray is many times more than those of α-ray and β-ray. γ-ray can penetrate an aluminum sheet of thickness 100 cm.

Question 10. Compare α-ray, β-ray, and γ-ray on basis of their ionising power.
Answer:

Comparison among α-ray, β-ray, and γ-ray on the basis of their ionising power discussed below:

α-ray	β-ray	γ-ray
α-ray has the maximum power to ionise gases. The ratio of power to ionise gases of α, β and γ-rays is  10000: 100 :1	β-ray has more power to ionise gases than γ-ray but less than that of α -ray.	γ-ray has less power to ionise gases than α-ray and β-ray.

Question 11. How does the nucleus of a radioactive atom change after the emission of an α-particle? Radium ( \({ }_{88}^{226} Ra\)) is converted into radon (Rn) by emission of one α-particle. Calculate the mass number and an atomic number of radon.
Answer:
1. If an α-particle is emitted from the nucleus of a radioactive atom, a new nucleus is formed whose mass number is reduced by 4 units and atomic number is reduced by 2 units.
\({ }_Z^A \mathrm{X} \stackrel{-\alpha \text {-particle }}{\longrightarrow}{ }_{Z-2}^{A-4} Y\)
(parent atom)  (daughter atom)

2. In this case, mass number of radon = 226-4 = 222 and atomic number = 88 – 2 = 86

Wbbse Class 10 Physical Science Solutions

Question 12. What is the ratio of masses of an α- particle and β-particle which are emitted from a radioactive atom? There is no electron in the nucleus of an atom. Then how is an electron emitted as a β-particle from atom of a radioactive element?
Answer: Mass of an α-particle/ Mass of a β-particle

= \(\frac{\text { mass of four protons (approx.) }}{\text { mass of one electron }}\)

= \(\frac{4 \times 1.6605 \times 10^{-27} \mathrm{~kg}}{9.1 \times 10^{-31} \mathrm{~kg}}\)

= 0.7299 x 104 = 7299 (approx.)

In the phenomenon of emission of a (β -particle from the nucleus of a radioactive atom, a neutron (n) is disintegrated to produce one proton (p) and one electron (e). The produced proton remains within the nucleus and the electron comes out of the nucleus with a very high velocity. This is the reason why an electron is emitted as a β-particle from the atom of a radioactive element, in spite of the fact that there is no electron in the nucleus.

Question 13. How does the nucleus of a radioactive atom change after emission of a β-particle? Thorium (\({ }_{90}^{234} Th\)) is converted into protactinium (Pa) by emission of one β particle. Calculate the mass number and atomic number of protactinium.
Answer: If a β-particle is emitted from the nucleus of a radioactive atom, a new nucleus is formed whose mass number remains unchanged but the atomic number increases by one unit.
\({ }_Z^A X \stackrel{-\beta \text {-particle }}{\longrightarrow}{ }_{Z+1}^A Y\)
(parent atom)  (daughter atom)

In this case, mass number of protactinium = 234 and atomic number = 90 + 1 = 91

Wbbse Class 10 Physical Science Solutions

Question 14. What is the ratio of charges of α-particle and β-particle? Why is lead present in the mineral of any radioactive metal?
Answer: Charge of α-particle / Charge of β-particle
= \(\frac{\text { charge of } 2 \text { protons }}{\text { charge of } 1 \text { electron }}\)
[∴ charge of 1 proton = charge of 1 electron]

Due to successive radioactive emissions from any radioactive element, it is ultimately converted into a non-radioactive isotope of lead (₈₂Pb). After this, there is no further radioactive decay. This is why lead is available in the mineral of any radioactive metal.

Structure of Atomic Nucleus Explained

Question 15. Write down the differences between an β-particle and an ordinary electron?
Answer: Differences between an β-particle and an ordinary electron:

β-particle	Ordinary electron
1. β-particle is emitted instantaneously after its creation in the nucleus of a radioactive atom.	1. Ordinary electrons remain in different orbits outside the nucleus of the atom.
2. After the emission of an β-particle from the nucleus of a radioactive element, the mass number of the new element remains the same but the atomic number increases by one unit.	2. An atom is converted into a positively charged ion after the emission of an ordinary electron from the atom.

Question 16. Write down the differences between a radioactive change and a chemical change.
Answer: The differences between a radioactive change and a chemical change:

Radioactive change	Chemical change
1. Radioactive change is a nuclear phenomenon	1. Chemical change is a phenomenon involving valence electrons in the orbits of the atom.
2. Radioactive change is not influenced by external pressure, light, catalyst, electric field or magnetic field.	2. Chemical change is influenced by external pressure, light, catalyst etc.
3. Radioactive change is a irreversible change.	3. Chemical change may be irreversible as well as reversible.
4. A new element is- formed in a radioactive change.	4. No news element is formed in a chemical change.
5. Huge amount of energy is produced in a radioactive change.	5. Amount of energy produced in a chemical change is less than that produced in a radioactive change. Moreover in some cases, energy is absorbed in a chemical change.

Question 17. An an α-particle is emitted from a nucleus X in the following way: \({ }_{92}^A X \longrightarrow \frac{228}{z} Y+\alpha\). Calculate the values of A and Z from the above reaction. Why is helium gas available in the mines of some radioactive metals?
Answer:
1. The new atom that is formed from the radioactive nucleus after emission of an α-particle gets its mass number and atomic number reduced by 4 units and 2 units, respectively.
A = 228+4 = 232 and Z= 92-2 = 90

2. α-particle that emits from a radioactive element in a mine of radioactive metals ionises the gas. The α-particle is converted into a helium atom by acquiring 2 electrons from the surroundings and remains inside the mine as helium gas.

Wb Class 10 Physical Science Question and Answers

Question 18. Mention three applications of radioactivity
Answer:

Applications of radioactivity:

Radioactive elements are used at present in many areas including medical science.
1. Radioactive elements radium, cobalt ( ⁶⁰Co) are used to destroy those cells which are affected by cancer. Radioactive phosphorus (³²P) is used for the treatment of leukemia and brain tumour. Radioactive iodine (¹³¹I) is used for the treatment of the disease of the thyroid.

2. Radioactive elements are used to determine the suitability of certain raw materials used in different industrial units.
3. A smoke detector has been manufactured on the basis of a special characteristic of the radioactive material {americium-241). This instrument can detect smoke which is emitted due to an accidental fire, and alarm the people by the sound of a siren.

Question 19. What is the mass number and atomic number of the new elementary particle that is produced when 8 α-particles and 6 β-particles are emitted successively (one after another) from the nucleus of \({ }_{92}^{238} U\)?
Answer: If one α-particle is emitted from the nucleus of any radioactive element, its mass number is reduced by 4 units and its atomic number is reduced by 2 units. If one β-particle is emitted, the mass number remains unchanged but the atomic number increases by 1 unit.

Since 8 α-particles and 6 β-particles are emitted 238 from the nucleus of \({ }_{92}^{238} U\), the mass number of the new element = 238 – (4 x 8) = 206 and atomic number = 92 – (2 x 8) + (1 x 6) = 92 – 16 + 6 + 82

Chapter 7 Atomic Nucleus Topic A Radioactivity Very Short Answer Type Questions Choose The Correct Answer

Question 1. Among the following rays, which one has the maximum power to ionise gases?

1. α
2. β
3. γ
4. Visible ray

Answer: 1. α

Question 2. Among the following rays, which one has the maximum penetrating power?

1. α
2. β
3. γ
4. Visible ray

Answer: 3. γ

Question 3. Among the following isotopes, which one is radioactive?

1. ¹²C
2. ¹⁴C
3. ¹⁶O
4. ²³Na

Answer: 2. ¹⁴C

Question 4. Speed of γ – ray in vacuum is

1. 2 × 10⁸  m/s
2. 3 × 10⁸  m/s
3. 1.5 × 10⁸  m/s
4. 2.5 × 10⁸  m/s

Answer: 2. 3 x 10⁸  m/s

Question 5. Charge of an a-particle is

1. 1.6 x 10^-19 C
2. 3.2 x 10^-19 C
3. 4.8 x 10^-19 C
4. 6.4 x 10^-19 C

Answer: 2. 3.2 x 10^-19 C

Wb Class 10 Physical Science Question and Answers

Question 6. What is the mass of a β-particle, if the mass of an electron is m?

1. m
2. 2m
3. 3m
4. 4m

Answer: 1. m

Question 7. Which of the following is used determination of the age of fossils?

1. ⁶⁰Co
2. ¹³¹I
3. ³²P
4. ¹⁴C

Answer: 4. ¹⁴C

Question 8. Who discovered radioactivity?

1. Ernest Rutherford
2. Madame Curie
3. Pierre Curie
4. Henry Becquerel

Answer: 4. Henry Becquerel

Question 9. If a powerful static electric field is applied in a perpendicular direction to the path of radioactive rays, which ray does bend towards the positively charged terminal?

1. α
2. β
3. γ
4. None of these

Answer: 2. β

Wb Class 10 Physical Science Question and Answers

Question 10. If a powerful static electric field is applied in a perpendicular direction to the path of radioactive rays, which ray. does bend towards the negatively charged terminal?

1. α
2. β
3. γ
4. None of these

Answer: 1. α

Question 11. The value of e/m of an α-particle is m of that of an ionised hydrogen.

1. Two times
2. Four times
3. Half
4. Equal

Answer: 3. Half

Question 12. If a powerful static electric field is applied in a perpendicular direction to the path of radioactive rays, which ray does not deviate?

1. α
2. β
3. γ
4. None of these

Answer: 3. γ

Question 13. The particle that escapes when β-decay (\({ }_{-1}^0 \mathrm{e}\)) takes place from the nucleus of an atom is

1. Neutrino
2. Antineutrino
3. Meson
4. Positron

Wb Class 10 Physical Science Question and Answers

Answer: 2. Antineutrino

Question 14. The new nucleus that is formed due to β- the decay of the nucleus of a \({ }_6^{14} \mathrm{C}\) atom is

1. \({ }_6^{13} \mathrm{C}\)
2. \({ }_7^{14} \mathrm{~N}\)
3. \({ }_5^{14} \mathrm{~B}\)
4. \({ }_8^{14} \mathrm{O}\)

Answer: \({ }_6^{13} \mathrm{C}\)

Question 15. Which of the following has a speed equal to that of light?

1. α-ray
2. β-ray
3. γ-ray
4. None of these

Answer: 3. γ-ray

Question 16. If an α-particle is emitted from the nucleus of \({ }_Z^A X\) atom thereby producing Y element, then the mass number and atomic number of Y are

1. A,2-2
2. A – 2, Z — 2
3. A – 4, Z- 2
4. 4-4, Z

Answer: 3. A – 4, Z- 2

Question 17. If a β-particle is emitted from the nucleus of \({ }_Z^A X\)atom thereby producing Y element, then the mass number and atomic number of Y are

1. A, Z
2. A+ 1,Z+l
3. A, Z + 1
4. A-1, Z-l

Answer: 3. A, Z + 1

Question 18. How many αparticles in succession to one α particle need to be emitted from the nucleus of an atom of X to make the new element an isotope of X?

1. 1
2. 2
3. 3
4. 4

Answer: 2. 2

Question 19. Which of the following is not radioactive?

1. ³²P
2. ¹⁴C
3. ⁴⁰K
4. ²³Na

Answer: 4. ²³Na

Question 20. If m is the mass of an electron, then the mass of a positron is

1. m
2. m/2
3. 2m
4. 4m

Answer: 1. m

Wb Class 10 Physical Science Question and Answers

Question 21. Particles that can be added to the nucleus of an atom without changing its chemical properties are

1. Neutrons
2. Electrons
3. Protons
4. Positrons

Answer: 1. Neutrons

Question 22. Which of the following particles are constituents of the nucleus?

1. Protons and electrons
2. Neutrons and electrons
3. Electrons and positrons
4. Neutrons and protons

Answer: 4. Neutrons and protons

Question 23. The mother and daughter elements with the emission of β-rays are

1. Isotopes
2. Isobars
3. Isomers
4. Isodiaphers

Answer: 2. Isobars

Question 24. The mother and daughter elements with the emission of γ-rays are

1. Isotopes
2. Isobars
3. Isomers
4. Isodiaphers

Answer: 3. Isomers

Question 25. The nuclei of \({ }_6^{13} \mathrm{C}\) and \({ }_7^{14} \mathrm{~N}\) can be described as

1. Isodiaphers
2. Isotones
3. Isobars
4. Isotopes

Answer: 2. Isotones

Question 26. 1 Curie is

1. 1 dps
2. 3 ×10¹⁰  dps
3. 3.7 ×10¹⁰  dps
4. 10⁶ dps

Answer: 3. 3.7 ×10¹⁰  dps

Question 27. In \({ }_{88}^{226} R\) nucleus, there are

1. 138 protons and 88 neutrons
2. 138 neutrons and 88 protons
3. 226 protons and 88 electrons
4. 226 neutrons and 138 electrons

Answer: 2. 138 neutrons and 88 protons

Question 28. An atomic number of a nucleus is 2 and its atomic mass is M. The number of neutrons is

1. M-Z
2. M
3. Z
4. M + Z

Answer: 1. M-Z

Wb Class 10 Physical Science Question and Answers

Chapter 7 Atomic Nucleus Topic A Radioactivity Answer In Brief

Question 1. α-ray is composed of which type of electrically charged particles?
Answer: α-ray is composed of positively charged particles.

Question 2. β-ray is composed of which type of electrically charged particles?
Answer: β-ray is composed of negatively charged particles.

Question 3. Among α-ray, β-ray, and γ-rays, which one is electrically neutral?
Answer: γ-ray is electrically neutral.

Question 4. Is α-ray scattered by an electric field?
Answer: Yes, α-ray is scattered by an electric field.

Question 5. What are radioactive elements?
Answer: Radioactive elements are those elements whose atoms spontaneously emit a type of special invisible radiation and get converted into atoms of new elements.

Question 6. Write down the names of three natural radioactive elements.
Answer: Polonium (Po), radium (Ra) and uranium (U) are three natural radioactive elements.

Isotopes and Their Significance

Question 7. Write down the names of two radioactive elements whose Z < 20.
Answer: \({ }_6^{14} \mathrm{C}\) and \({ }_6^{14} C\) are two radioactive elements whose Z < 20.

Question 8. In between \({ }_6^{12} C\) and \({ }_6^{14} \mathrm{C}\), which one is radioactive?
Answer: \({ }_6^{14} \mathrm{C}\) is radioactive.

Question 9. Arrange the following rays according to the descending order of penetrating power: α-ray/ β-ray,γ-ray.
Answer: α-ray>β-ray>γ-ray

Wb Class 10 Physical Science Question and Answers

Question 10. Arrange the following rays according to the ascending order of power to ionise gases: α-ray/ β-ray,γ-ray.
Answer: α-ray<β-ray<γ-ray

Question 11. Write down the name of an instrument that measures radioactivity.
Answer: G-M Counter (Geiger-Muller Counter) measures radioactivity.

Question 12. Which element is responsible for the radioactivity of potassium uranyl sulphate?
Answer: Uranium is responsible for the radioactivity of potassium uranyl sulphate.

Question 13. What is the effect of radioactivity on the cells of a living organism?
Answer: The effect of radioactive rays on a cell may be fatal as it may destroy active cells.

Question 14. How many protons in the nucleus are reduced if one α-particle is emitted from the nucleus of a radioactive element?
Answer: Two protons are reduced in the nucleus if one α-particle is emitted from the nucleus of a radioactive element.

Question 15. How many neutrons in the nucleus are reduced if one α-particle is emitted from the nucleus of a radioactive element?
Answer: Two neutrons are reduced in the nucleus if one α-particle is emitted from the nucleus of a radioactive element.

Question 16. How many types of ray are emitted from a radioactive substance? Write down their names.
Answer: Three types of ray are emitted from a radioactive substance, namely alpha (α) ray, beta (β) ray, and gamma (γ) ray.

Physical Science Class 10 West Bengal Board

Question 17. Among the rays which are emitted from a radioactive material, which is an electromagnetic wave?
Answer: Among the rays which are emitted from a radioactive material, a gamma ray is an electromagnetic wave.

Question 18. Of all the rays emitted from a radioactive material, which rays have particle nature?
Answer: Of all the rays emitted from radioactive material, α-ray and β-ray are streams of particles with masses and thus, have a particle nature.

Question 19. Which is massless among α, β, and γ-rays?
Answer: γ-ray is massless.

Question 20. Where does radioactive change take place inside an atom?
Answer: Radioactive change takes place in the nucleus of the atom.

Question 21. Is a radioactive change unidirectional or bidirectional?
Answer: A radioactive change is always unidirectional.

Question 22. A compound of a radioactive element is formed a chemical reaction. Is there any change does occur in radioactivity?
Answer: Radioactivity remains unchanged even if a compound of a radioactive element is formed in a chemical reaction.

Question 23 A is a radioactive element. A is converted to element B by emitting successively one α-particle and two β-particles. What is the relation between A and B?
Answer: If the atomic number of element A is Z, then the atomic number of element B becomes Z-2 + 1 + 1-Z.
∴ A and B are isotopes of each other.

Physical Science Class 10 West Bengal Board

Question 24. What is the SI unit of radioactivity?
Answer: SI unit of radioactivity is becquerel (Bq).

Question 25. The atomic number is not changed by which type of radioactive decay?
Answer: γ – decay.

Question 26. Helium ions and α-particles are the same or different?
Answer: Helium ions and α-particles are the same.

Question 27. What type of radioactive decay is caused when there are too many neutrons in the nucleus?
Answer: β-decay.

Question 28. Which part of an atom undergoes a change in the process of radioactive decay?
Answer: The nucleus of an atom undergoes a change in the process of radioactive decay.

Question 29. Name the radioactive radiation which have the least penetrating power.
Answer: ‘α’-radiation have the least penetrating power.

Physical Science Class 10 West Bengal Board

Question 30. A radioactive substance is oxidised. What change takes place in the nature of radioactivity?
Answer: No change takes place.

Applications of Nuclear Physics in Daily Life

Question 31. Name the positively charged particle that emanates from an uranium nucleus.
Answer: The positively charged particles that emanate from an uranium nucleus is ‘α’- particle.

Question 32. Name a negatively charged radioactive – particle.
Answer: A negatively charged radioactive particle is β-particle.

Question 33. Why are emissions of α-particles, β-particles, and γ-rays called nuclear phenomenon?
Answer: These emissions are entirely nuclear phenomenon because that happens due to internal changes in the nucleus.

Physical Science Class 10 West Bengal Board

Chapter 7 Atomic Nucleus Topic A Radioactivity Fill In The Blanks

Question 1. After emission of one _______ particle, \({ }_{13}^{28} \mathrm{Al}\) is transformed into \({ }_{14}^{28} \mathrm{Si}\).
Answer: β

Question 2. γ-ray is a type of ______  wave.
Answer: Electromagnetic

Question 3. The atom of the radioactive element which undergoes radioactive decay is called ______ atom.
Answer: Parent

Question 4. The atom of the new element that is produced after emission of a radioactive ray from the nucleus is called a ______  atom.
Answer: Daughter

Question 5. The rest mass of γ-ray is ______.
Answer: Zero.

Question 6. The age of a fossil and an archaeological object is determined by measuring the ratio of _______ and ¹²C in it.
Answer: ¹⁴C.

Question 7. The charge of an α-particle is_______ of that of a hydrogen ion.
Answer: Twice

Question 8. If an α-ray falls on a screen coated with zinc sulfide, it creates ______.
Answer: Fluorescence

Question 9. α-particle is the nucleus of a  atom.
Answer: Helium

Physical Science Class 10 West Bengal Board

Question 10. Atomic number of a radioactive nucleus is not affected due to emission of ______ ray from it.
Answer: γ

Question 11. Charge of the positron is ______.
Answer: +1.6 10^-19 C

Question 12. Radioactivity is totally a ______  phenomenon.
Answer: Nuclear

Question 13. When a radioactive element emits one alpha particle, its atomic no ______ by 2 and mass number ______ by 4.
Answer: Decreases and Decreases

Question 14. The radioactive, nature of two uranium isotopes \({ }_{92}^{235} U\) and \({ }_{92}^{238} U\) are ______.
Answer: Different.

Question 15. When a radioactive element emits one ______  particle, its atomic number increases by 1.
Answer: β

Wbbse Class 10 Physical Science Chapter 7 Question And Answers

Question 16. ¹³¹I isotope is used to test the activity of ______  gland.
Answer: Thyroid

Chapter 7 Atomic Nucleus Topic A Radioactivity State Whether True Or False

Question 1. Nucleon is a collective name for two particles, the neutron, and proton.
Answer: True

Question 2. An electron has a greater mass than a proton.
Answer: False

Question 3. When an or-particle is ejected, the atomic number of the atom decreases by 2.
Answer: True

Question 4. β-ray has the highest penetrating power.
Answer: False

Question 5. Isotopes are the atoms having same atomic number but different mass number.
Answer: False

Question 6. β-rays and cathode rays are identical in nature.
Answer: True

Question 7. No radioactive sample can emit all three radiations α, β and γ-simultaneously.
Answer: True

Question 8. γ rays can be completely absorbed in 1/10mm thick aluminum plate.
Answer: False

Chapter 7 Atomic Nucleus Topic B Nuclear Energy Synopsis

1. The mass of a nucleus is slightly less than the mass of the sum of protons and neutrons present in the nucleus. This difference between the two masses is called the mass defect(Δm).

The atomic number and the mass number of the atom are Z and A respectively. If the masses of the proton and the neutron are mp and mn respectively and the mass of the nucleus of the atom is M, then mass defect, \(\Delta m=Z \cdot m_p+(A-Z) m_n-M\).

2. Binding energy is defined as the minimum energy required to disassemble a nucleus of an atom into its constituent particles. It is the equivalent amount of energy of mass defect.

Wbbse Class 10 Physical Science Chapter 7 Question And Answers

If Δm is mass defect then according to Einstein’s mass-energy relation binding energy =Δmc²

3. Binding energy per nucleon is the average energy required to release a nucleon from the nucleus. Binding energy per nucleon ∝ stability of the nucleus.

4. The Einstein equivalent of mass and energy can be stated as: If the mass m of a body is completely converted to energy, then the measure of the energy is
E=mc², c = speed of light in vacuum.

5. Unified atomic mass unit: 1/12th of the mass of a ¹²C atom is called 1 amu or 1 u.

∴ \(1 \mathrm{u}=\frac{1}{12} \times \frac{12}{6.022^{\prime} \times 10^{23}} \mathrm{~g}\)= 1.6605 x 10^-27 kg

6. If 1 u mass is completely converted into energy, the amount of energy produced
E = mc², m = 1 u = 1.6605 x 10^-27 kg,c = 2.998 x 10⁸  ms^-1 = 1.6605 x 10^-27 x (2.998 x 10⁸)²J =14.920008 X 10^-11 J
≈ 931 MeV (1 eV= 1.6602 x 10^-19 J, 1 MeV = 106 eV)

7. Nuclear Fission is the process of splitting of a heavy nucleus into two lighter nuclei of almost equal masses with the liberation of energy.
Example: When \({ }_{92}^{235}U\) nuclei bombarded with slow neutrons, exploded into two fragments ₅₆Ba and ₃₆Kr.

\(\begin{array}{r}
{ }_{92}^{235} U+{ }_0^1 \mathrm{n} \rightarrow{ }_{92}^{236} \mathrm{U}^\rightarrow{ }_{56}{ }^{141} \mathrm{Ba}+{ }_{36}^{92} \mathrm{Kr}+{ }_{30}^1 \mathrm{n} \\ +\text { energy } \end{array}\)

The energy released in \({ }_{92}^{235}U\) fission is about 200 MeV. A nuclear reaction sustained by the product of the initial reaction leading from one reaction to the other consecutively, is called chain reaction.

Wbbse Class 10 Physical Science Chapter 7 Question And Answers

When one neutron is bombarded on \({ }_{92}^{235}U\) target then 3 neutrons are released. They are j slowed down to thermal neutron. Now they are used for further fission of \(3_{92}^{235}U\) nuclei releasing 9 new neutrons and so on.

8. A nuclear reactor is a device in which nuclear fission can be carried out through a sustained and controlled chain reaction. Main component of a nuclear reactor: Uranium isotopes (U²³⁵), Thorium isotope (Th²³²) etc are most commonly used fuels in the reactor.

10. Moderator is used to slow down the fast moving neutrons. Most commonly used moderators are graphite and heavy water (D₂O).
11. Control material is used to control the chain reaction and to maintain a stable rate of reaction. Cadmium rods are used as control material. (Steel rod with a coating of boron is also used as a control rod)

12. Most commonly used coolants are water, N_2,CO_2.
13. Uses of nuclear reactor are:
(1)In electric power genertaion
(2) To produce radioisotopes etc.

14. Nuclear Fusion is a process in which two light nuclei are fused or combined at a very high temperature to form a heavy nucleus. This process releases a large amount of energy. High pressure (≈ 10⁶ atm) and high temperature (≈ 10⁷ K to 10⁸K are required for fusion. So the fusion reaction is called a thermonuclear reaction.

Examples:
1. \(
{ }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H} \stackrel{\text { Fusion }}{\longrightarrow}{ }_2^3 \mathrm{He}+{ }_1^0 \mathrm{n}+\text { energy }
(3.7 MeV)\)

Two \({ }_1^2 \mathrm{H}\) nuclei are fused to produce a \({ }_2^3 \mathrm{He}\) nucleus, a neutron, and energy (3.7 MeV approx).

2. In the Sun and some stars the source of energy is the fusion of protons to form a helium nucleus, positrons, and energy.

\(\begin{array}{r}
{ }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H} \stackrel{\text { Fusion }}{\longrightarrow}{ }_2^4 \mathrm{He}+2{ }_1^{\mathrm{O}} \mathrm{e} \\
+\text { energy (26 MeV) }
\end{array}\)

Chapter 7 Atomic Nucleus Topic B Nuclear Energy Short And Long Answer Type Questions

Question 1. What is nuclear reaction? Write down Einstein’s principle of equivalence of mass and energy.
Answer:

Nuclear reaction:

1. Nuclear reaction is a process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce one or more nuclides that are different from the initial nuclide(s).

2. According to Einstein’s theory of relativity, mass is concentrated energy. It is possible to convert mass into energy and energy into mass. If an amount of mass m of a substance is converted fully into energy, then an amount of energy E=mc² is released where c = 2.998 x 10⁸m/s = speed of light in vacuum.

Question 2. What is mass defect? Calculate the mass defect of the nucleus with mass M .Given, the mass of a proton = m_p and the mass of a neutron = m_n.
Answer:

Mass defect:

1. The mass of a nucleus is slightly less than the mass of the sum of protons and neutrons present in the nucleus. This difference between the two masses is called the mass defect.

2. According to the above question, the atomic number and the mass number of the atom are Z and A, respectively. If the masses of the proton respectively and the mass of the nucleus of the atom is M, then the total mass of the nucleons = Z • m_p + (A – Z)m_n.
∴ mass defect = Z • m_p + (A – Z)m_n – M

Question 3. What is binding energy? Calculate the binding energy of the nucleus with mass M. Given the mass of a proton = m_p and the mass of a neutron = m_n.
Answer:

Binding energy:

1. Binding energy is defined as the minimum energy required to disassemble a nucleus of an atom into its constituent particles. It is the equivalent amount of energy of mass defect.

2. According to the above question, the atomic number and the mass number of the atom are Z and A, respectively. If the masses of the proton and the neutron are m_p and m_n, respectively and the mass of the nucleus of the atom is M, then total mass of the nucleons = Z • m_p + (A-Z)m_n
∴ mass defect = Z • m_p + (A – Z)m_n– M and hence binding energy = {Z-m_p + (A-Z)m_n-M}c2
∴ where c is the speed of light in vacuum.

Wbbse Class 10 Physical Science Chapter 7 Question And Answers

Question 4. Calculate the equivalent amount of energy when 1 u of mass is converted fully into energy. Calculate the binding energy of a ⁴He₂ nucleus. Given, m_n = 1.007276 u,m_n = 1.008665, mass of  ⁴He₂ nucleus = 4.001505u.
Answer:
1. Here, m = 1u = 1.66 x 10^-27 kg
According to the equation E=mc², the equivalent amount of energy = 1.66 x 10^-27 x (2.998 x 10⁸)² = 14.92008 x 10^-13nJ
Again, 1 MeV = 1.6022 x 10^-13 J

\(E=\frac{14.92008}{1.6022} \times \frac{10^{-11}}{10^{-13}} \mathrm{MeV}\)= 931.2 MeV or, 1 u =931.2 MeV.

2. Mass defect of ⁴He₂ nucleus = (2m_p+2 m_n)-M = (2 X 1.007276 + 2 X 1.008665) – 4.001505 = 0.0304 u (approx.)
∴ binding energy of ⁴He₂ nucleus = 0.0304 x 931.2 MeV = 28.3 MeV (nearly)

Question 5. What do you mean by a chain reaction? What is a nuclear reactor?
Answer:

Chain reaction:

1. In nuclear fission due to the bombardment of neutrons on each ²³⁵U atom, high speed neutrons are ejected from the reaction. These are called secondary neutrons. These secondary neutrons interact with the surrounding uranium nucleus.

If sufficient fissile fuel is present, some of these neutrons may be absorbed and cause more fissions. Thus, the cycle repeats and the process of nuclear fission continues spontaneously. This type of spontaneous reaction is called a chain reaction.

2. A nuclear reactor is an arrangement used to initiate and control a sustained nuclear chain reaction. Nuclear reactors are used at nuclear power plants mainly for electricity generation.

Common Mistakes in Understanding Atomic Structure

Question 6. What is nuclear fission?

\(
{ }_{92}^{235} \mathrm{U}+{ }_0^1 \mathrm{n} \longrightarrow{ }_{54}^{134} \mathrm{xe}+{ }_{38}^{100} \mathrm{Sr}+{ }_2^1 \mathrm{n}
[235.0439u] [1.0087u] [133.9054u] [99.9354u] +
energy \)

Wbbse Class 10 Physical Science Chapter 7 Question And Answers
How much mass is reduced in the given nuclear fission?
Answer: Breaking up of a heavy nucleus into two nuclei of almost equal masses is called nuclear fission.

In the given equation, initial mass before reaction,
m₁ = mass of U-235 nucleus + mass of a neutron = 235.0439 + 1.0087 = 236.0526 u

Final mass after reaction, m₂ = mass of (Xe-134 + Sr-100 + 2 neutrons)= 133.9054 + 99.9354 + 2 x 1.0087 = 235.8583U

∴ reduction of mass, m = m₁ -m_{2 =} 236.0526 – 235.8583 = 0.1944 u

Question 7. Write down the names of some non conventional sources of energy other than atomic energy. What are the advantages in the production of atomic energy?
Answer: Some sources of non-conventional energy other than atomic energy are solar energy, wind energy tidal energy etc. Production of atomic energy is not affected by any natural event like cyclones, storms, rain, earthquakes etc. Atomic energy can be produced day and night over all the year. But this advantage is not there in the case of the production of other energies. This is the advantage of the production of atomic energy.

Question 8. What are the advantages of atomic energy as a fuel compared to fossil fuel?
Answer:

Advantages of atomic energy over energy from fossil fuel:

Energy from fossil fuel	Atomic Energy
1. Due to the rampant use of fossil fuels (like coal, petrol, diesel, kerosene etc.), amount. of carbon dioxide and other Greenhouse gases is increasing in the atmosphere.	1. Production of harmful gases reduce owing to the use of atomic energy.
2. The amount of fossil fuel used to get a certain amount of energy is slowly pushing us towards a serious fuel crisis. This is a major problem at present for human civilisation.	2. A huge amount of energy is available due to nuclear fission from a very small amount of material. This is not possible from any other source and also is a great savior compared to any other fuel. For example, nearly 3000 tons of coal have to be burnt to get the same amount of energy (nearly 7.4 x 1010J) that is available from fission of only 1 g of U-235.

Question 9. Why is a fission reaction carried out before a fusion reaction? Several lacs of people were killed in Japan in 1945 due to the explosion of an atomic bomb. In 1986, the nuclear reactor at Chornobyl of Ukraine went out of control and the residents of that town suffered nearly the same fate. Is.there any difference in the scientific causes of these two incidents?
Answer:
1. 10⁷°C to 10⁸°C temperature is required for fusion of the nuclei. This high temperature cannot be produced in a simple way This high temperature can be produced by the process of takes place before a fusion reaction.

2. The first incident was due to the bad intention of a class of warmongers. Due to uncontrolled nuclear fission, huge amount of heat energy is produced in this type of atomic explosion. Radioactive radiation is also emitted in it. Due to these two reasons, a lot of people were killed.

The second one was simply an undesirable accident. In a nuclear reactor, heat energy is converted into electrical energy by causing controlled nuclear fission. In other words, atomic energy is utilised in a peaceful way through this process for the welfare of mankind.

But unfortunately, on 26th April 1986, the process of nuclear fission in a nuclear reactor at Chornobyl of Ukraine went out of control and emitted a huge amounts of radioactive rays. As a result, the residents of the city became the victims of radioactivity for a long time.

Question 10. What are used as:
1. Fuel,
2. Moderator,
3. Control rods and
4. Coolant in a nuclear reactor and what are their functions?

Answer:

Name of the part	Main material used	Function
1. Fuel	Uranium (a radioactive element) [U-235]	U-235 is bombarded with thermal neutrons bringing about fission.
2. Moderator	Heavy water (D2O ) or graphite	Neutrons with high kinetic energy generated due to nuclear reactions are slowed down by it
3. Control rods	Cadmium (Cd), hafnium (Hf), or boron (B) coated steel rods	To absorb excess thermal neutrons that are not required.
4. Coolant	Generally water	To absorb heat energy that is produced in the core due to nuclear reactions

 

Question 11. Explain nuclear fusion with an example. Explain the main source of energy for sun and other stars.
Answer:
1. An example of nuclear fusion is given below.

\({ }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H} \longrightarrow{ }_2^3 \mathrm{He}+{ }_0^1 \mathrm{n}+\text { energy }\)

Here, two deuterium nuclei combine together to form one helium ( ³He₂) nucleus and one neutron. The sum of the masses of helium ( ³He₂) and neutron is slightly less than the sum of the masses of two deuteriums. This reduced mass is converted into energy.

2. The main process of producing energy for any star like sun is nuclear fusion. The main fuel of a star is hydrogen. The process of fusion in a star is brought about through some cycles. Generally, it is said that in each cycle, four hydrogen (¹H₁) nuclei join to produce one helium (⁴He₂) and two positrons (⁰e₁).

Physical Science Class 10 West Bengal Board

\(4_1^1 \mathrm{H} \longrightarrow{ }_2^4 \mathrm{He}+2_1^0 \mathrm{e}\)

The sum of the masses of one helium (⁴He₂ ) and two positrons (⁰e₁) is less than the combined mass of four hydrogen nuclei. This decrease in mass is transformed into energy. In sun 12 crore tons of hydrogen is converted into helium in every minute and a huge amount of heat energy is thus produced. The sun has been radiating heat energy in this way for the last 460 crore years.

Question 12. What is nuclear fusion?
\(\begin{aligned}
& { }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H} \longrightarrow{ }_2^3 \mathrm{He}+{ }_0^1 \mathrm{n} \text { +energy } \\
& {[2.015 \mathrm{u}]} \\
&
\end{aligned}\)
Calculate the amount of energy released in this process by talking 1u = 931.2 MeV.
Answer:
1. Nuclear fusion is a process in which two light nuclei are fused or combined at a very high temperature to form a heavy nucleus. This process releases a large amount of energy.

2. Mass of 2 deuterons in the given equation before reaction, m₁ = 2 x 2.015 = 4.030 u.

Final mass after reaction, m₂ =\({ }_2^3 \mathrm{He}+{ }_0^1 n\) = 3.017 + 1.009 = 4.026 u decrease in mass, m = m₁ – m₂ = 4.030-4.026 = 0.004 u
amount of energy released = 0.004 u equivalent amount of energy = 931.2 x 0.004 = 3.725 MeV (approx.)

WBBSE Class 10 Revision Notes on Atomic Nucleus

Question 13. Write down the diffreneces between nuclear fission and nuclear fussion.
Answer:

The differences between nuclear fission and nuclear fusion are:

Nuclear fission	Nuclear fusion
1. A heavy nucleus is split into two nuclei of almost equal masses in this process.	1. A few light nuclei are fused together to form a heavy nucleus in this process.
2. The energy produced in this process is less than the energy produced by the fusion of materials of equal masses.	2. The energy produced in this process is more than the energy produced by fission of equal masses.
3. Thermal neutrons are required in this process to bombard the target nucleus.	3. No bombarding particle is required in this process.
4. This process takes place at normal -temperature.	4. This process takes place at a temperature between 107oC and 108oC.
5. Radioactive rays are emitted in this process.	5. No radioactive rays are emitted in this process.

Chapter 7 Atomic Nucleus Topic B Nuclear Energy Very Short Answer Type Questions Choose The Correct Answer

Question 1. The main cause of solar energy is

1. Nuclear fission and fusion
2. Nuclear fission
3. Nuclear fusion
4. Chemical reaction

Answer: 3. Nuclear fusion

Question 2. \({ }_{92}^{235} U+{ }_0^1 n \longrightarrow{ }_{56}^{141} B a+{ }_{36}^{92} \mathrm{Kr}+{ }_0^1 n\)

1. 1
2. 2
3. 3
4. 4

Answer: 3. 3

Question 3. What is the average binding energy of each nucleon inside a nucleus to make the nucleus stable?

1. Nearly 2 MeV
2. Nearly 2.5 MeV
3. Nearly 3 MeV
4. Nearly 8 MeV

Answer: 4. Nearly 8 MeV

Question 4. 1 eV = how many J?

1. 3.2 × 10^-19
2. 1.6 × 10^-19
3. 4.8 × 10^-19
4. 6 4 × 10^-19

Answer: 2. 1.6 x 10^-19

Question 5. 1 MeV = how many J?

1. 1.6 × 10^-13
   
2. 3.2 × 10^-13
3. 4.8 × 10^-13
4. 6.4 × 10^-13

Answer: 1. 1.6 x10^-13

Question 6. Binding energy per nucleon is maximum in

1. ⁶⁰Ni
2. ⁵⁶Fe
3. ⁵⁸Fe
4. ⁶²Ni

Answer: 4. ⁶²Ni

Question 7. Value of binding energy per nucleon of 62Ni is approximately

1. 8.0 MeV
2. 9.2 MeV
3. 8.8 MeV
4. 8.2 MeV

Answer: 3. 8.8 MeV

Question 8. How many times more energy is released during fusion of 1 g of hydrogen than during fission of lg of uranium ( ²³⁵U₉₂)?

1. 2.3
2. 4.3
3. 7.3
4. 10.3

Answer: 3. 7.3

Question 9. How much energy is produced if 0.1 u amount of mass is converted into energy?

1. 186.3 MeV
2. 46.575 MeV
3. 93.12 MeV
4. 372.6 MeV

Answer: 3. 93.12 MeV

Question 10. Size of the nucleus is of the order of

1. 10^-10 m
2. 10^-15 m
3. 10^-12 m
4. 10^-19 m

Answer: 2. 10^-15 m

Question 11. Nuclear binding energy is equivalent to

1. Mass of proton
2. Mass of neutron
3. Mass of nucleus
4. Mass defect of nucleus

Answer: 4. Mass defect of nucleus

Question 12. The energy equivalent to 1 kg of matter is about

1. 10^-15 J
2. 10 J
3. 10^-10 J
4. 10^{17 J}

Answer: 4. 10^{17 J}

Question 13. Average binding energy per nucleon in the nucleus of an atom is approximately

1. 8eV
2. 8 keV
3. 8 MeV
4. 8J m

Answer: 3. 8 MeV

Question 14. A moderator is used in nuclear reactor in order to

1. Slow down the speed of the neutrons
2. Accelerate the neutrons
3. Increase the number of neutrons
4. Decrease the number of neutrons

Answer: 1. Slow down the speed of the neutrons

Question 15. The control rod in a nuclear reactor is made of

1. Uranium
2. Cadmium
3. Plutonium
4. Graphite

Answer: 2. Cadmium

Question 16. The process by which a heavy nucleus splits into light nuclei is known as

1. Fission
2. Fusion
3. Chain reaction
4. Meltdown

Answer: 1. Fission

Question 17. During the nuclear fusion reaction

1. A heavy nucleus breaks into two fragments by itself
2. A light nucleus bombarded by thermal neutrons breaks up
3. A heavy nucleus bombarded by thermal neutrons breaks up
4. Two light nuclei combine to give a heavier nucleus and possible other products

Answer: 4. Two light nuclei combine to give a heavier nucleus and possible other products

Question 18. Fusion reaction takes place at high temperature because

1. Atoms are ionised at high temperature
2. Molecules break up at high temperature
3. Nuclei break up at high temperature
4. Kinetic energy is high enough to overcome repulsion between nuclei

Answer: 4. Kinetic energy is high enough to overcome repulsion between nuclei

Question 19. The explosion of the atomic bomb takes place due to

1. Nuclear fission
2. Nuclear fusion
3. Melting
4. Evaporation

Answer: 1. Nuclear fission

Question 20. The mass equivalent of 931 MeV energy is

1. 1.66 × 10^-27 kg
2. 6.02 × 10^-24 kg
3. 1.66 × 10^-20 kg
4. 9.11 × 10^-31 kg

Answer: 1. 1.66 × 10^-27 kg

Question 21. A chain reaction continues due to

1. Large mass defect
2. Large energy
3. Production of more neutrons in fission
4. High temperature

Answer: 3. Production of more neutrons in fission

Question 22. Heavy water ( D²O) is used as moderator in a nuclear reactor. The function of the moderator is

1. To control the energy released in the reactor
2. To absorb neutrons and stop chain reaction
3. To cool the reactor fast
4. To slow down the speed of neutrons

Answer: 4. To slow down the speed of neutrons

Chapter 7 Atomic Nucleus Topic B Nuclear Energy Answer In Brief

Question 1. What is the temperature required to bring about nuclear fusion?
Answer: Nuclear fusion takes place at a temperature of 10^7oC to 10^8oC.

Question 2. What is the main source of energy for the sun and the stars?
Answer: Nuclear fusion is the main source of energy for the sun and the stars

Question 3. Name one radioactive material which is much used as fuel in a nuclear reactor.
Answer: Uranium, a radioactive material, is generally used as fuel in a nuclear reactor.

Question 4. What is the role of heavy waters in a nuclear reactor?
Answer: Heavy water is used in a nuclear reactor to slow down the speed of neutrons.

Question 5. The binding energy of the ⁴He₂  nucleus is 28.2 MeV. What do you understand by this statement?
Answer: The given statement means that a minimum energy of 28.2 MeV is required to separate 2 protons and 2 neutrons from a helium nucleus to make them free.

Question 6. Which element has the highest binding energy per nucleon?
Answer: ⁶²Ni has the highest binding energy per nucleon.

Question 7. What do you understand by mass defect?
Answer: The mass of a nucleus is slightly less than the mass of the sum of protons and neutrons present in the nucleus, this difference of two masses is called the mass defect.

Question 8. What is binding energy of a nucleus?
Answer: Nuclear binding energy is the minimum energy that is required to disassemble the nucleus of an atom into its component parts, i.e., neutrons and protons.

Question 9. Who did invent the formula of equivalence of mass and energy?
Answer: Albert Einstein invented the formula.

Word Problems Related to Atomic Structure

Question 10. Write down Einstein’s formula for mass-energy equivalence.
Answer: Formula: E=mc², where m = mass of material, c – speed of light in vacuum, and E is the amount of energy equivalent to mass m.

Question 11. What is nuclear fission?
Answer: Nuclear fission is the process of splitting of a heavy nucleus into two lighter nuclei of comparable masses with the liberation of energy.

Question 12. What is the main source of energy gained in nuclear fusion or fission?
Answer: The main source of energy gained in nuclear fusion or fission is a decrease or reduction in mass.

Question 13. Which nuclear process was followed to manufacture an atomic bomb?
Answer: Nuclear fission was followed to manufacture an atom bomb.

Question 14. Which particle is used as a bombarding particle to bombard the target nucleus in the process of nuclear fission?
Answer: Neutron is used as a bombarding particle.

Question 15. How much energy is produced if 1 u amount of mass is converted into energy?
Answer: 931.2 MeV (approx.) energy is produced if lu amount of mass is converted into energy.

Question 16. What is a thermal neutron?
Answer: A neutron with a high kinetic energy of about 10^-2 eV is called thermal neutron.

Physical Science Class 10 West Bengal Board

Question 17. Write down an use of thermal neutron.
Answer: Thermal neutron is used to split a heavy nucleus into two or more lighter nuclei in nuclear fission.

Question 18. Is the Particle produced in nuclear fusion radioactive or non-radioactive?
Answer: The particle produced in nuclear fusion is non-radioactive.

Question 19. Which process is carried out in a nuclear reactor?
Answer: The process of nuclear fission is carried out in a controlled way in a nuclear reactor.

Question 20. Can nuclear fission process be controlled?
Answer: Yes, the process of nuclear fission can be controlled.

Question 21. Complete the following reaction: \({ }_{88}^{226} R a \longrightarrow ?+{ }_{86}^{222} R n\)
Answer: \({ }_{88}^{226} \mathrm{Ra} \rightarrow{ }_2^4 \mathrm{He}+{ }_{86}^{222} \mathrm{Rn}\)

Question 22. Complete the following reaction: \({ }_6^{14} C \longrightarrow ?+{ }_7^{14} N\)
Answer: \({ }_6^{14} \mathrm{C} \rightarrow{ }_{-1}^0 \mathrm{e}+{ }_7^{14} N\)

Question 23. Complete the following reaction: \({ }_{90}^{234} \mathrm{Th} \longrightarrow{ }_{91}^{234} \mathrm{~Pa}+?\)
Answer: \({ }_{90}^{234} \mathrm{Th} \rightarrow{ }_{91}^{234} \mathrm{~Pa}+{ }_{-1}^0 \mathrm{e}\)

Question 24. Complete the following reaction: \({ }_{92}^{238} \mathrm{U} \longrightarrow ?+{ }_2^4 \mathrm{He}\)
Answer: \({ }_{92}^{238} \mathrm{U} \rightarrow{ }_{90}^{234} \mathrm{Th}+{ }_2^4 \mathrm{He}\)

Question 25. What is the amount of nuclear binding energy corresponds to mass defect Am?
Answer: Nuclear binding energy corresponds to mass defect Δm is = Δm . c², c = speed of light in vacuum.

Question 26. The expected mass of a helium nucleus is 4.0320 u and its actual mass is 4.0015 u. Find its mass defect.
Answer: Mass defect of a helium nucleus is Δm = 4.0320 – 4.0015 = 0.0305 u.

Question 27. What is the relation between mass defect and nuclear binding energy?
Answer: Nuclear binding energy is energy equivalent to the mass defect of a nucleus.

Question 28. Is the law of conservation of mass applicable in case of nuclear reaction?
Answer: In case of nuclear reaction the law of conservation of mass is not applicable.

Physical Science Class 10 West Bengal Board

Question 29. Is the law of conservation of mass number and the law of conservation of atomic number applicable in case of nuclear reaction?
Answer: Yes, the law of conservation of mass number and the law of conservation of atomic number are applicable in case of nuclear reaction.

Visual Representation of Atomic Nucleus Models

Question 30. What is a nuclear reactor?
Answer: A nuclear reactor is an arrangement used to initiate and control a sustained nuclear chain reaction.

Question 31. What is the role of moderators in a nuclear reactor?
Answer: Moderator is used to slowing down the speed of neutrons.

Question 32. What is the role of the control rod in a nuclear reactor?
Answer: The control rod absorbs surplus thermal neutrons.

Question 33. What material is generally used as a control rod in a nuclear reactor?
Answer: Cadmium rod or steel rod with a coating of boron is generally used as a control rod.

Chapter 7 Atomic Nucleus Topic B Nuclear Energy Fill In The Blanks

Question 1. The mass of a nucleus is slight ______ than the sum of the masses of neutrons and protons present in that nucleus.
Answer: Less

Question 2. The process of nuclear ______  is carried out before nuclear fusion takes place.
Answer: Fission

Question 3. Mass of the nucleus of deuterium (²H₁) is ______ than the sum of masses of one proton and one neutron.
Answer: Less

Physical Science Class 10 West Bengal Board

Question 4. The main cause in producing energy for the sun is nuclear ________.
Answer: Fusion

Question 5. The fusion process occurs at a very high temperature. Such a process is called a _______  reaction.
Answer: Thermonuclear

Question 6. ________  is used as a projectile particle in a nuclear fission reaction.
Answer: Thermal/Slow

Question 7. Heavy water (D²O) is used as a _______ in nuclear reactors.
Answer: Moderator

Question 8. The greater is the binding energy the more ______  is the nucleus.
Answer: Stable

Chapter 7 Atomic Nucleus Topic B Nuclear Energy State Whether True Or False

Question 1. High-energy neutrons are used in a nuclear reactor to initiate the fission reaction.
Answer: False

Question 2. Cadmium rods are used as moderators in a nuclear reactor.
Answer: False

Physical Science Class 10 West Bengal Board

Question 3. The higher the mass defect the higher is the stability of the nucleus.
Answer: False

Question 4. \({ }_0^1 \mathrm{n}+{ }_7^{14} \mathrm{~N} \longrightarrow{ }_1^0 \mathrm{H}+{ }_6^{15} \mathrm{C}\)
Answer: False

Question 5. The conversion of lu of mass results in 931.2 x 10⁶ eV of energy.
Answer: True

Question 6. In sun and other stars, the energy is produced by nuclear fusion.
Answer: True

Question 7. Mass defect is always positive.
Answer: True

Question 8. Electron is used as an ideal particle for bombarding.
Answer: False

Question 9. Hydrogen bomb is made on the basis of nuclear fission reaction.
Answer: False

Question 10. The Fukushima nuclear plant disaster was a nuclear accident caused by a natural disaster tsunami.
Answer: True

Chapter 7 Atomic Nucleus Miscellaneous Type Questions Match The Columns

Question 1.

Column A	Column B
α-particle	1. Electromagnetic radiation
β-particle	2. 1H2
γ-ray	3. He2+
Deuteron	4. e-

Answer:
α-particle: 3. He²⁺
β-particle: 4. e- 
γ-ray: 1. Electromagnetic radiation
Deuteron: 2. ₁H²

Question 2.

Column A	Column B
α-decay	1. Unchanged nucleus
β -decay	2. Decrease in mass number
γ-decay	3. Increase in atomic number

Answer:
α-decay: 2. Decrease in mass number
β -decay:  3. Increase in atomic number
γ-decay: 1. Unchanged nucleus

Question 3.

Column A	Column B
1 u	1. 6.642 X 10-24 g
Mass of α-particle	2. E = mc2
Equivalence of mass and energy	3. 1H2 + 1H2 →2He3  + 0n1
Nuclear fusion	4. 931.2 MeV

Answer:
1 u: 4. 931.2 MeV
Mass of α-particle:  1. 6.642 X 10^-24 g
Equivalence of mass and energy: 2. E = mc²
Nuclear fusion: 3. ₁H² + ₁H² _→2He³  + ₀ⁿ¹

WBBSE Solutions for Class 10 Physical Science and Environment

 

Chapter 4 Phenomena Of Heat Topic A Thermal Expansion of Solid, Liquid and Gas Synopsis

WBBSE Class 10 Chemical Calculations Overview

1. If the temperature of a solid substance is increased, its area and volume also expand: This phenomenon is called the thermal expansion of a solid substance.

2. Thermal expansion of a solid is of three types:
(1)Expansion of length
(2)Expansion of area
(3)Expansion of volume.

3. The coefficient of linear expansion of a solid is the fractional increase in its length per degree rise in temperature. It is generally denoted by or. If l₁ and l₂  are the lengths of a solid substance (say a metallic rod) at temperatures t₁ and t₂ respectively, then \(\alpha=\frac{l_2-l_1}{l_1\left(t_2-t_1\right)}\)

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4. Unit of coefficient of surface expansion, \(=\frac{\text { unit of length }}{\text { unit of length } \times \text { unit of temperature }}\),\(=\frac{1}{\text { unit of temperature }}\)

Therefore, unit of a is independent of unit of length and it depends on the unit of temperature. So, CGS unit of α is °C^-1 , in SI it is K^-1 and in FPS system its unit is °F^-1.

5. The change in temperature by 1°F = 5/9°C change in temperature.
∴ value of α in Fahrenheit scale (α_F) = 5/9 X value of or in Celsius scale (α_c).

6. The change in temperature by 1K = 1°C change in temperature
∴ Value α in Kelvin ( α_k) = value of α in Celsius scale (α_c).
i..e., α_k=α_c= 9/5α_F

7. The coefficient of surface expansion of a solid is the fractional increase in its surface area per degree rise in temperature. It is generally denoted by β. If S₁ and S₂ are the surface areas of a solid at temperatures t₁ and t₂ respectively, then \(\beta=\frac{S_2-S_1}{S_1\left(t_2-t_1\right)}\).

Wb Class 10 Physical Science Solutions

8. Unit of coefficient of surface expansion \(=\frac{\text { unit of area }}{\text { unit of area } \times \text { unit of temperature }}\) , \(=\frac{1}{\text { unit of temperature }}\)

Unit in CGS system is °C^-1  , in SI it is K^-1, and in FPS system it’s unit is °F^-1 .

9. The coefficient of volume expansion of a solid is the fractional increase in its volume per degree rise in temperature. It is usually denoted by γ. if V₁ and V₂ are the volumes of a solid at t₁ and t₂ respectively, then coefficient of volume expansion, \(\gamma=\frac{V_2-V_1}{V_1\left(t_2-t_1\right)}\)

10. Unit of coefficient of volume expansion γ, \(=\frac{\text { unit of volume }}{\text { unit of volume } Χ \text { unit of temperature }}\) = \(=\frac{1}{\text { unit of temperature }}\)

Unitin CGS system is °C^-1  , in SI it is K^-1, and in FPS system its unit is °F^-1.

10. Relation among α, β and γ is α = β/2 = γ/2

11. ln case of a liquid kept in a vessel, if the expansion of the vessel is neglected, the expansion of the liquid that is obtained is the apparent expansion of the liquid. In the case of the same liquid kept in a vessel, if the expansion of the vessel is taken into consideration along with the apparent expansion of the liquid, then the expansion of the liquid is called the real expansion of the liquid.

12. The coefficient of real expansion of a liquid is the ratio of actual expansion in volume to its original volume for each degree rise in temperature.

13. The coefficient of apparent expansion of a liquid is the ratio of apparent expansion in volume to its original volume for each degree of rise in temperature. The relation between the coefficients of real and apparent expansions of a liquid is given by γ_r = γ_a + γ_g

where γ_r and γ_a are the respective, coefficients of real and apparent expansions of the liquid and γ_g is the coefficient of volume expansion of the substance of the vessel in which the liquid is kept.

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14. The units of coefficient of apparent or real expansion of a liquid depend only on the unit of temperature and not on the unit of volume. The unit of each is °C^-1  or °F^-1 or K^-1  and the dimensional coefficient is Θ^-1.

15. By keeping the pressure on a definite mass of gas constant, if the temperature is raised from 0°C to 1°C, then the ratio of expansion in volume to the initial volume of a gas is called coefficient of volume expansion of that gas and it is expressed as γ_p.

Suppose, V₀ and V_t are the respective volumes of a definite mass of gas at 0°C and t°C at constant pressure. Then we can write, \(\gamma_p=\frac{V_t-V_0}{V_t t} \text { or, } V_t=V_0\left(1+\gamma_p t\right)\).

16. Coefficient of volume expansion of an ideal gas, \(\gamma_p=\frac{1}{273}{ }^{\circ} \mathrm{C}^{-1}\)

Chapter 4 Phenomena Of Heat Topic A Thermal Expansion of Solid, Liquid and Gas Short And Long Answer Type Questions

Understanding Molar Mass in Chemical Calculations

Question 1. What is the thermal expansion of a solid substance? There are two scales for measurement of length (distance). One is made of invar and the other of iron. Which one of these two is more suitable for measuring accurately the distance between two definite places in different times of the year Give a reason for your answer.

Answer:

The thermal expansion of a solid substance

1. If the temperature of a solid substance is increased, the volume of the substance expands. This expansion due to the increase of temperature is called the thermal expansion of a solid substance.

2. The temperature of a place is different during different seasons of the year. The distance between two places does not depend on the temperature. But if the measuring scale is made of a metal, the length of the scale changes according to the temperature. As a result, different readings are found for the same length at different times of the year with this scale.

3. Invar has a coefficient of linear expansion (1.2 x 10^-6K^-1 at 20°C) which is much lower than the coefficient of linear expansion of iron (11.8 x 10^-6K^-1 at 20°C). This means that the change in length of a scale made of invar is insignificant compared to the change in length of an equal scale made of iron. For this reason, a scale made of invar is more suitable for the measurement of distance.

Wb Class 10 Physical Science Solutions

Question 2. Write the expression for the coefficient of linear expansion of a solid. What do you mean by the statement that the coefficient of linear expansion of iron is 12 x 10^-6/°C?

Answer:
1. Suppose l₁ is the length of a solid substance at temperature t₁ and the length becomes l₂  when the temperature is raised to t₂ . If α is the coefficient of linear expansion of the solid substance, then according to the definition, \(\alpha=\frac{l_2-l_1}{l_1\left(t_2-t_1\right)}\)

The above statement means that if the temperature, of an iron rod is increased by 1°C, 12 x 10^-6 part of its original length increases.

Question 3. There are several rods of same length and made of the same substance. What is the change in their lengths for a different increase in their temperatures? Show that: the unit of coefficient of linear expansion does not depend on the unit of length but depends only on the unit of temperature.

Answer:
1. The change in lengths of the rods made of the same substance and having the same length is directly proportional to the change in temperature. Therefore more the temperature is increased, the more is the change in length of the rod. The ratio between the change in temperature and the change in this length is constant.

Mathematically, change in length ex-change in temperature or, (l₁-l₂) ∝ (t₂ -t₁)

2. Suppose, l₁ is the 1ength of a rod at temperature t_1. It is heated to a higher temperature t₂ when its length becomes l₂. Hence, the coefficient of linear expansion,

∴ \(\alpha=\frac{l_2-l_1}{l_1\left(t_2-t_1\right)}\)

\(\frac{l_2-l_1}{l_1}\) is the ratio of two quantities having the same dimension. So it has no unit. Therefore, the coefficient of linear expansion depends only on the unit of (t₂  t₁), i.e., on the unit of temperature.

Wb Class 10 Physical Science Solutions

Question 4. There are several rods of different, lengths made of the same substance. If the temperature of the rods Is increased by the same amount, what is the change in their lengths? A stopper made of steel gets stuck firmly in the mouth of a bottle made of brass. How can you open it?

Answer:
1. The change in length of the rods made of the same substance and of different lengths is directly proportional to the lengths of the rods for the same increase of temperature, in other words, more the initial length of the rod, more is the change of length of the rod. The ratio between the initial length and the change in length is constant.

∴ Mathematically, change in length ∝ initial length or, (l₁-l₂) ∝ l₁

2. The coefficient of linear expansion for brass is greater than that for steel. If the system is heated, the expansion of brass is more than that of steel. As a result, the stopper is stuck all the more. But if the system is cooled, the contraction of brass is more than that of iron. Hence, the stopper loosens and comes out.

Question 5. How does the length of a rod depend on the initial length of the expanding rod (l₂) and on difference of temperature (Δt)? Establish a relationship between the coefficients of linear expansion in the Celcius and Fahrenheit scales.

Answer: Expansion of length (Δl) is directly proportional to the initial length of the rod and increase in temperature (Δt), i.e. Δl ∝Δl₁ [when Δt remains the same] and Δl ∝ Δt [when l₁ is constant]
∴ Δl ∝ l₁Δt[when both l₁ and Δt change]

Let us assume that the coefficient of linear expansion of a solid substance, α = x/°C.
Again, we know that, change by 1°C = change by 9/5°F

\(\alpha=\frac{x}{\frac{9}{5} \circ \mathrm{F}}=\frac{5}{9} x /{ }^{\circ} \mathrm{F}\)

Hence, if the coefficients of linear expansion are α_c and α_F respectively, then = α_F 5/9 α_c.

Question 6. Explain what happens when a bimetallic strip made of brass and iron is heated.

Answer: For the same increase in temperature, different solid substances of the same length have different amount of expansion. The coefficient of linear expansion of brass is more than that of iron. The lengths of brass and iron are the same in the bimetallic strip. As the linear expansion of brass is more than that of iron for the same rise in temperature, the bi-metallic strip bends with brass remaining outside.

Question 7. There Is one rod of iron, one iron scale and one invar scale in a room. The temperature of the room changes every hour. By which scale, the length of the rod is to be measured so that no change of length is observed? Establish the condition to maintain a constant difference in the lengths of two rods at all temperatures.

Answer: For the same change in temperature, change in length of invar is negligible compared to the change in length of iron which is much more. As the rod is made of iron, its change in length per unit length is equal to the change in length per unit length of the scale, with the same change in temperature. As a result, no change in length of the rod is noticed if the length of rod is measured with the iron scale.

Let us assume that at temperature t_1, lengths of the two rods are l₁ and l₂ ( l₁ > l₂ ). After the temperature increases to t₂, the lengths of these two rods become l’₁  and l’₂ respectively. Let the coefficients of linear expansion of these rods be α₁ and α₂ respectively.

According to the given condition,

\(l_1-l_2=l_1^{\prime}-l_2^{\prime}\) or, \(l_1^{\prime}-l_1=l_2^{\prime}-l_2\)

or, \(l_1 \alpha_1\left(t_2-t_1\right)=l_2 \alpha_2\left(t_2-t_1\right)\)

or, \(l_1 \alpha_1=l_2 \alpha_2\) or, \(\frac{l_1}{l_2}=\frac{\alpha_2}{\alpha_1}\)

This is the required condition.

Wbbse Class 10 Physical Science And Environment

Question 8. An iron rod is fixed along the diameter of a circular iron ring. If the system is heated uniformly, does the ring remain circular? Explain.

Answer:

Given

An iron rod is fixed along the diameter of a circular iron ring. If the system is heated uniformly,

Suppose, the length of the iron rod, is l₁ =1.
Let the length of the iron ring be l₂.
So, the diameter of the circle = l and the length of the iron ring, l₂ = πl

∴\(\frac{l_2}{l_1}=\frac{\pi l}{l}=\pi\)

Suppose, increase in temperature of the system = t
Now, the length of the iron rod, l’₁  = l(1+ αt) [where a is the coefficient of linear expansion of iron] and length in the iron] and length in the iron ring l’₂ = πl(1 +αt)

∴ \( \frac{l_2^{\prime}}{l_1^{\prime}}=\frac{\pi l(l+\alpha t)}{l(l+\alpha t)}=\pi\)

As the ratio of the circumference of the circle and diameter remain the same in both cases, the ring remains circular.

Examples of Chemical Calculation Problems

Question 9. Write the expression for the coefficient of surface expansion for solid. Show that the unit of coefficient of area expansion does not depend on the unit of area but only on the unit of temperature.

Answer: Let the coefficient of surface expansion be denoted by β.

If S₁ and S₂ are the surface areas of a solid at temperatures t₁ and t₂  respectively, then the increase in surface area is (S₂ – S₁) with a rise in temperature of ( t₂ – t₁).

∴ \(\beta=\frac{S_2-S_1}{S_1\left(t_2-t_1\right)}\)

Here \(\frac{\left(S_2-S_1\right)}{S_1}\) is a ratio of two similar quantities and thus does not have any unit. Therefore, the unit of coefficient of surface expansion depends only on the unit of ( t₂ – t₁) i.e., on the unit of temperature.

Wbbse Class 10 Physical Science Chapter 4 Question Answer

Question 10. On which factors and how does the surface expansion of a solid depend? Why is some gap left between two iron plates in a joint of a bridge?

Answer: Suppose, the surface area of a solid is S₁ at temperature t₁. If the temperature is increased to t₂, the area becomes S₂ .
Thus, expansion of area = (S₂ – S₁) and increase of temperature = (t₂ – t₁).

Therefore, the expansion of area is directly proportional to the initial area of the solid and also on the increase in temperature.
∴ (S₂ – S₁) α S₁ [when (t₂ – t₁) remains the same] and (S₂ – S₁) ∝ (t₂ – t₁) [when S₁ is constant]
i.e., S₂ – S₁ ∝ t₂ – t₁ [when both S₁  and (t₂ – t₁) are changing]

A solid get expansion due to an increase of temperature. The iron plates of the joints of a bridge are heated by the sun’s rays and require sufficient space for expansion. For this reason, some gap is left between the two plates. Without this gap, one iron plate puts pressure on another due to thermal expansion. As a result, the bridge may get damaged.

Question 11. Write down the expression for the coefficient of volume expansion of solid. Show that the unit of coefficient of volume expansion does not depend on the unit of volume but depends only on the unit of temperature.

Answer:
1. Let the expression be denoted by γ. If V₁ and V₂ are the volumes of a solid at temperatures t₁ and t₂ respectively, then the increase in volume is (V₂ – V₁) with a rise in temperature of (t₂ – t₁).

∴\(\gamma=\frac{V_2-V_1}{V_1\left(t_2-t_1\right)}\)

\(\gamma=\frac{\text { increase in volume }}{\text { initial volume } \times \text { increase in temperature }}\)

 

Therefore, unit of coefficient of volume expansion \(=\frac{\text { unit of volume }}{\text { unit of volume } \times \text { unit of temperature }}\) = \(=\frac{1}{\text { unit of temperature }}\)

Hence, unit of coefficient of volume expansion depends only on the unit of temperature.

Common Mistakes in Chemical Calculations

Question 12. What do you mean by the statement that the coefficient of volume expansion of iron is 36 x 10^-6/°C? A roof casting generally needs rods of iron but not of any other metal explain why?

Answer:
1. The coefficient of volume expansion of iron is 36 x 10^-6/°C means that with a rise of temperature of 1°C, the volume increases by 36 x 10^-6 of its initial volume.

Alternative answer: The coefficient of volume expansion of iron is 36 x 10^-6/°C. Thus, if the temperature of 1cm³ or 1m³ of iron is increased by 1°C, the volume of iron increases by  36 x 10^-6cm³ or 36 x 10^-6m³.

2. During casting, iron rods are entered into concrete. In summer, temperature is high and so both concrete and rod undergo thermal expansion. On the other hand, temperature is low in winter and both of them contract. It has been found that the coefficient of expansion for both are almost equal. That is why only iron rods are used during casting. Expansion or compression of any other metal does not match with that *of concrete and as a result, cracks develop in the casting.

Question 13. Two Identical sheets, one of copper and the other of iron, are riveted together. What happens if this system is heated? What happens if the temperature of this system is decreased?

Answer:

Given

Two Identical sheets, one of copper and the other of iron, are riveted together.

The coefficient of linear expansion of copper is greater than that of iron. So, with the same increase in temperature, linear expansion of copper is more than that of iron. As the two sheets are riveted together, this pair of sheets bend. Expansion of copper being more, it remains outside.

With the decrease in temperature, this pair of sheets bend. Contraction of copper being more, it remains inside copper.

Question 14. Establish the relation between apparent and real expansions of a liquid with the help of a simple experiment.

Answer:
Experiment: At first, a glass flask fitted with a stopper is taken. A thin glass tube is entered through the stopper and a scale is fixed with the tube. A portion of the tube and the entire glass flask are filled with a coloured liquid. Let the initial level of liquid in the tube be A.

Now this flask is immersed in a vessel filled with hot water. It can be observed that the level of liquid comes down from A to B. Then the level of liquid goes up slowly to C.

Conclusion: When the flask is immersed in hot water, glass gathers heat from water and expands itself. This is the reason why the level of liquid in the tube comes down from A to B. Then heat is transmitted to liquid through glass and liquid expands so that its level in the tube goes up.

From this experiment, it is clearly understood that the volume of the liquid in the glass tube between points A and B is the measure of expansion of the vessel and the volume of the liquid in the glass tube between points, S and C is the measure of real expansion of the liquid. If we ignore the expansion of the vessel, the expansion of the liquid is called apparent expansion.

Therefore, the volume of the liquid in the glass tube between points A and C represents the apparent expansion of liquid.
Here, BC = AB+AC
Hence, real expansion of the liquid = expansion of volume of the vessel + apparent expansion of the liquid.

Question 15. What is the coefficient of apparent expansion of a liquid? What are the factors on which the apparent expansion of a liquid depends?

Answer: The coefficient of apparent expansion of a liquid is the ratio of apparent expansion in volume to its original volume for each degree rise in temperature.

The apparent expansion of a liquid depends on the following factors:
1. Initial volume of the liquid
2. Increase of temperature
3. Nature of the liquid
4. Substance of the vessel.

Wbbse Class 10 Physical Science And Environment

Question 16. Write the expression for the coefficient of apparent expansion of a liquid. A right circular cylinder contains liquid. If the cylinder is heated, the level of liquid in it remains unchanged. How is it possible?

Answer:
1. Suppose, the volume of a definite mass of a liquid is V₁ at temperature t₁ and if the temperature is increased to t₂, its apparent volume is V₂.

Therefore, coefficient of real expansion of the liquid \(\gamma_r=\frac{V_2-V_1}{V_1\left(t_2-t_1\right)}\)

2. Unit of the coefficient of real expansion of a liquid is °C^-1  or °F^-1 or K^-1  .

Question 17. What is the coefficient of real expansion of a liquid? What are the factors on which the real expansion of a liquid depends?

Answer:

1. The coefficient of real expansion of a liquid is the ratio of actual expansion in volume to its original volume for each degree rise in temperature.

2. The real expansion of a liquid depends on the following factors:
(1)Initial volume of the liquid 0 Increase in temperature
(2)Nature of the liquid.

WBBSE Class 10 Revision Notes on Chemical Calculations

Question 18. Between the coefficients of apparent and real expansions, which does measure the inherent property of a liquid?

Answer:

1. To measure the coefficient of thermal expansion of a liquid, it must be kept in a vessel. The coefficient of apparent expansion of a liquid depends on the coefficient of volume expansion of the vessel.

2. For different vessels made of different substances, coefficients of apparent expansion are different; but the coefficient of real expansion remains unchanged. Therefore, between the coefficients of apparent and real expansions, coefficient of real expansion measures the inherent property of a liquid.

Question 19. Write the expression for the coefficient of apparent expansion of a liquid. A right circular cylinder contains liquid. If the cylinder is heated, the level of liquid in it remains unchanged. How is it possible?

Answer:

Suppose, the volume of a definite mass of a liquid is V₁ at temperature t₁ and if the temperature is increased to t₂, its apparent volume is V’₂.

Therefore, coefficient of apparent expansion of the liquid, γ_a = \(\gamma_a=\frac{V_2^{\prime}-V_1}{V_1\left(t_2-t_1\right)}\)

If the cylinder and the liquid equally expand for a increase in temperature, no change occurs in the level of liquid in the cylinder. In this case, the coefficient of apparent expansion of the liquid is zero.

Wbbse Class 10 Physical Science And Environment

Question 20. Write the expression for coefficient of volume expansion of a gas and calculate its value with the help of Charles’ law.

Answer:

Suppose, the volume of a definite mass of gas at 0°C is V/Q. Under constant pressure if the temperature is increased to t°C, the volume becomes Vt.

By definition of coefficient of volume expansion, we may write \(\gamma_p=\frac{V_t-V_0}{V_0 t}\) ……(1)

From equation (1), we get, V_t – V₀ =V₀ γ_pt or, V_t=V₀+γ_pt or, V_t= V₀(l + γ_pt)
Again, we get from Charles’ law, \(V_t=V_0\left(1+\frac{t}{273}\right)\) …..(3)

By comparing equations (2) and (3), we get the value of coefficient of volume expansion of a gas as \(\gamma_p=\frac{1}{273}{ }^{\circ} \mathrm{C}^{-1}=3.663 \times 10^{-3 \circ} \mathrm{C}^{-1}\).

Question 21. What do you mean by apparent expansion and real expansion of liquid? A liquid has coefficient of apparent expansion but in case of a gas, why is the coefficient of apparent expansion not taken into consideration?

Answer:

Apparent expansion of liquid: In case of a liquid kept in a vessel, if the expansion of the vessel is neglected, the expansion of the liquid that is obtained is called the apparent expansion of the liquid.

Real expansion of liquid: In case of a liquid kept in a vessel, if the expansion of the vessel is taken into consideration along with the apparent expansion of the liquid, the expansion of the liquid is called the real expansion of the liquid.

Both liquid and gaseous substances have to be kept inside a vessel and then heated. As a result, expansion of the vessel also takes place along with the expansion of liquid or gas. Expansion of solid is less than the expansion of liquid but, it cannot be neglected. But in case of a gas, expansion of the vessel is not considered as the expansion of solid is 1/100th part of the expansion of a gas taken in it. For this reason, coefficient of apparent expansion of gas is not taken into account.

Chapter 4 Phenomena Of Heat Topic A Thermal Expansion of Solid, Liquid and Gas Very Short Answer Type Questions

Question 1. Unit of coefficient of surface expansion depends

1. Only on the unit of area
2. Only on the unit of temperature
3. On the units of area and temperature
4. On the units of temperature and time

Answer: 2. Only on the unit of temperature

Question 2. Dimensional formula of coefficient of volume expansion is

1. L³ Θ^-1  
2. Θ^-2
   
3. LΘ^-1 
4. Θ^-1

Answer: 4. Θ^-1

Question 3. The value of the coefficient of volume expansion of gas is

1. 1/273 °C^-1 
2. 2/273 °C^-1 
3. 4/273 °C^-1 
4. 1/91 °C^-1 

Answer: 1. 1/273 °C^-1 

Question 4. The initial temperature at the time of expansion of gas is taken as

1. Any temperature
2. 0K
3. 0°C
4. 4°C

Answer: 3. 0°C

Question 5. Which of the following liquids displays anomalous expansion?

1. Mercury
2. Kerosene
3. Glycerine
4. Water

Answer: 4. Water

Question 6. Expansion of the length of a solid depends on

1. Initial length
2. Increase in temperature
3. The material
4. All of the above

Answer: 4. All of the above

Question 7. If the coefficient of linear expansion of a solid substance is 27xlO-6/°C, what is the value in Fahrenheit scale?

1. 12 x 10^-6°F^-1
2. 16 × 10^-6°F^-1
3. 15 × 10^-6°F^-1
4. 18 × 10^-6°F^-1

Answer: 3. 15 × 10^-6°F^-1

Question 8. Which of the following has practically no expansion in spite of increase in temperature?

1. Iron
2. Nickel
3. Steel
4. Invar (nickel-iron alloy)

Answer: 4. Invar (nickel-iron alloy)

Question 9. If α, β and γ are the coefficients of linear expansion, surface expansion and volume expansion of a solid substance respectively, then

1. α has the highest value
2. β has the highest value
3. γ has the highest value
4. α, (β and γ have equal values

Answer: 3. γ has the highest value

Question 10. If the lengths of a solid substance with α as the coefficient of linear expansion are l₁ and l₂ at temperatures. t₁ and t₂ respectively (where t₂ > t₁ ), then

1. \(\alpha=\frac{l_2-l_1}{t_2-t_1}\)
2. \(\alpha=\frac{l_1}{\left(l_2-l_1\right)\left(t_2-t_1\right)}\)
3. \(\alpha=\frac{\left(l_2-l_1\right)^2}{l_1\left(t_2-t_1\right)}\)
4. \(\alpha=\frac{l_2-l_1}{l_1\left(t_2-t_1\right)}\)

Answer: 4. \(\alpha=\frac{l_2-l_1}{l_1\left(t_2-t_1\right)}\)

Question 11. If the surface areas of a solid substance with β as the coefficient of surface expansion are S₁ and S₂ at temperatures t₁ and t₂ respectively (where t₂ > t₁ ), then

1. \(\beta=\frac{S_2-S_1}{t_2-t_1}\)
2. \(\beta=\frac{S_2}{\left(S_2-S_1\right)\left(t_2-t_1\right)}\)
3. \(\beta=\frac{S_2-S_1}{S_1\left(t_2-t_1\right)}\)
4. \(\beta=\frac{S_2}{S_1\left(t_2-t_1\right)}\)

Answer: 3. \(\beta=\frac{S_2-S_1}{S_1\left(t_2-t_1\right)}\)

Question 12. If the volumes of a solid substance with γ as the coefficient of volume expansion are V₁ and V₂ at temperatures and t₂ respectively (where t₂ > t₁), then

1. \(\gamma=\frac{V_2-V_1}{V_1\left(t_2-t_1\right)}\)
2. \(\gamma=\frac{V_2-V_1}{t_2-t_1}\)
3. \(\gamma=\frac{V_2\left(t_2-t_1\right)}{\left(V_2-V_1\right)}\)
4. \(\gamma=\frac{V_1\left(t_2-t_1\right)}{\left(V_2-V_1\right)}\)

Answer:1. \(\gamma=\frac{V_2-V_1}{V_1\left(t_2-t_1\right)}\)

Question 13. If the temperature of a metallic rod of length 4 m is increased by 2°C, its length increases by 88 x 10^-6m . α of this rod is

1. 9 x 10^-6 °C^-1 
2. 10 x 10^-6 °C^-1
3. 11 X 10^-6 °C^-1
4. 12 x 10^-6 °C^-1

Wbbse Class 10 Physical Science Solutions

Answer: 3. 11 × 10^-6 °C^-1

Question 14. If the coefficients of linear expansion of a solid substance are ac and α_F in Celcius and Fahrenheit scales respectively, then

1. α_F = 5/9 α_c
2. α_F = 9/5 α_c
3. α_F = 5/8 α_c
4. α_F = 5/6 α_c

Answer: 1. α_F = 5/9 α_c

Question 15. The temperatures of two iron rods of lengths 1 m and 2 m are increased to the same extent. What is the ratio of expansion of their lengths?

1. 1:2
2. 1:4
3. 1:8
4. 2:1

Answer: 1. 1:2

Question 16. If any solid substance is heated, which parameter is extended?

1. Only length
2. Only area
3. Only volume
4. All the three

Answer: 4. All the three

Question 17. There are two rods made of the same substance, each of length l. But their radii are r and 2 r, respectively. If the temperatures of both the rods are increased by the same amount, then

1. The length of the first rod increases more
2. The length of the second rod increases more
3. Both increase by the same length
4. It is not possible to predict their expansion

Answer: 3. Both increase by the same length

Question 18. There is a hole in the middle of a metal sheet. What happens if the temperature is increased?

1. Radius of the hole decreases
2. Radius of the hole increases
3. Radius of the hole remains unchanged
4. It is not possible to say whether the radius of the hole will increase or decrease

Answer: 2. Radius of the hole increases

Wbbse Class 10 Physical Science Solutions

Question 19. There are two spheres made of the same substance and having the same radii, one is solid but the other is hollow. If the temperature of both the spheres is increased by the same amount, then

1. Expansion of the hollow sphere is more
2. Expansion of the solid sphere is more
3. Both have the same expansion
4. It is not possible to say which sphere will have more expansion

Answer: 3. Both have the same expansion

Question 20. There are two holes of radii r₁ and r₂ (r_{1 >} r₂) inside a metallic plate. If the metallic plate is heated

1. Value of r₁ increases, value of r2 decreases
2. Values of both r₁ and r₂ increase
3. Values of both r₁ and r₂ decrease
4. Value of r₁ decreases, value of r₂ increases

Answer: 2. Values of both r₁ and r₂ increase

Question 21. A metallic rod is attached along the diameter of a circular metal plate. Both are made of the same element. If the system is heated, the ratio of the circumference and the diameter of the circle is

1. π
2. π/2
3. π/4
4. π/6

Answer: 1. π

Question 22. The dimension of the coefficient of surface expansion of a solid is

1. 1 in length, 2 in mass, 1 in temperature
2. 1 in length, 2 in time, 1 in temperature
3. -1 in temperature
4. 2 in temperature

Answer: 3. -1 in temperature

Question 23. The dimension of the coefficient of volume expansion of a solid is

1. 2 in length, 1 in temperature
2. 2 in mass, 1 in temperature
3. 1 in length, 1 in temperature
4. -1 in temperature

Answer: 4. -1 in temperature

Wbbse Class 10 Physical Science Solutions

Question 24. Volume expansion of a solid depends

1. Only on the initial volume
2. Only on the rise of temperature
3. Only on the coefficient of volume expansion
4. On all the above

Answer: 4. On all the above

Question 25. Surface expansion of a solid depends

1. Only on the initial surface area
2. Only on the rise of temperature
3. Only on the coefficient of surface expansion
4. On all the above

Answer: 4. On all the above

Question 26. For accurate measurement during expansion of a liquid, initial temperature is taken as

1. 0°c
2. 0K
3. 4°c
4. 10°c

Answer: 1. 0°c

Question 27. If the thermal conductivity of glass, k = 0.0025 cal •cm^-1 • °C^-1  • s^-1, then its value in SI is

1. 1.05 W • m^-1 • K^-1
2. 1.1 W • m • K^-1
3. 1 W • m^-1• K^-1
4. 1.2 W • m^-1 • K^-1

Answer: 1. 1.05 W • m^-1 • K^-1

Question 28. If the temperatures on the two sides of a heated rod are the same, then the value of thermal conductivity of the rod (in the unit cal •cm^-1 • °C^-1  • s^-1) is

1. 1
2. 0.5
3. 1000
4. ∞

Answer: 4. ∞

Question 29. There are two rods A and B of lengths lt and l2, and coefficients of linear expansion a± and az, respectively. What is the condition for the difference between the two lengths to remain unchanged at any temperature?

1. \(I_1 \alpha_1^2=I_2 \alpha_2^2\)
2. \(l_1^2 \alpha_1=I_2^2 \alpha_2\)
3. \(I_1 \alpha_2=I_2 \alpha_1\)
4. \(I_1 \alpha_1=I_2 \alpha_2\)

Answer: 4. \(I_1 \alpha_1=I_2 \alpha_2\)

Question 30. The volume of an iron sphere is 1000 cm3. What is the new volume of the sphere if the temperature is increased by 4°C? 7 for iron = 36 x 10-6^-1.

1. 0.15 cm³
   
2. 0.144 cm³
   
3. 0.154 cm³
   
4. 0.16 cm³

Answer: 2. 0.144 cm³

Question 31. When an aluminium ball is heated, the largest percentage increase will occur in its

1. Diameter
2. Area
3. Volume
4. Density

Answer: 3. Volume

Question 32. A bar of iron is 100 cm long at 20°C. At 19°C it will be (a of iron = 11 x 10^-6 /°C)

1. 11 x 10^-5 cm longer
2. 11 x 10^-6 cm shorter
3. 11 x 10^-4 cm shorter
4. 11 x 10^-4 cm longer

Answer: 3. 11 x 10^-4 cm shorter

Question 33. A solid ball of metal has a concentric spherical cavity within it. If the ball is heated, the volume of a cavity will

1. Increase
2. Decrease
3. Remain unaltered
4. First increases then decreases

Answer: 1. Increase

Question 34. When a bimetallic strip is heated, it

1. Does not bend at all
2. Get twisted in the form of a helix
3. Bends in the form of an arc with the more expandable metal outside
4. Bend in the form of an arc with the more expandable metal inside

Answer: 3. Bends in the form of an arc with the more expandable metal outside

Question 35. The coefficient of superficial expansion of a solid is 2×10^-5/°C- It’s coefficient of linear expansion is

1. 4 x 10^-5/°C
2. 3 x 10^-5/°C
3. 2 x 10^-5/°C
4. 1 x 10^-5/°c

Answer: 4. 1 x 10^-5/°c

Question 36. If the length of a cylinder on heating increases by 2%. The area of the base will increase by

1. 0.5%
2. 2%
3. 1%
4. 4%

Answer: 4. 4%

Chapter 4 Phenomena Of Heat Topic A Thermal Expansion of Solid, Liquid and Gas Answer In Brief

Question 1. The container has no role in the expansion of which—solid or liquid?
Answer: The container has no role in the expansion of solid.

Question 2. There are two spheres made of the same substance and also have equal radii. One of them is solid and the other is hollow. If the same amount of heat is given to both the spheres, which one expands more?
Answer: The hollow sphere expands more.

Question 3. What is the unit of coefficient of linear expansion of solid?
Answer: The unit of coefficient of linear expansion of solid is °C^-1  or °F^-1 or K^-1.

Question 4. Write one use of a bimetallic strip.
Answer: Bimetallic strip is used as thermostat.

Question 5. A bimetallic strip is made up of two metals A and B. The coefficient of linear expansion of A is more than that of B. If the bimetallic strip is heated, it bends. Which metal remains inside the curvature?
Answer: Metal B remains in the inside portion of the curvature.

Question 6. A bimetallic strip is made up of two metals A and B. The coefficient of linear expansion of A is more than that of B. If the bimetallic strip is cooled, it bends. Which metal remains inside the curvature?
Answer: Metal A remains in the inside portion of the curvature.

Question 7. What is the coefficient of linear expansion of a solid?
Answer: The coefficient of linear expansion of a solid is the fractional increase in length per degree rise in temperature.

Question 8. Does the unit of coefficient of linear expansion of a solid depend on the unit of length?
Answer: No, it does not depend on the unit of length.

Question 9. What is the coefficient of surface expansion of a solid?
Answer: The coefficient of surface expansion of a solid is the fractional increase in area per degree rise in temperature.

Question 10. Does the unit of coefficient of surface expansion of a solid depend on the unit of area?
Answer: No, it does not depend on the unit of area.

Question 11. Define the coefficient of volume expansion of a solid substance.
Answer: The coefficient of volume expansion of a solid is the fractional increase in volume per degree rise in temperature.

Question 12. Does the unit of coefficient of volume expansion of a solid depend on the unit of volume?
Answer: No, it does not depend on the unit of voiume.

Question 13. A scale made of brass is graduated at 0°C. What error may arise in the measurement of a certain distance with this scale at 30°C?
Answer: If a distance is measured by the given scale at 30°C, the reading obtained is less than the actual length.

Question 14. A scale made of brass is graduated at 0°C. 1 What error may arise in the measurement of a certain distance with this scale at 10°C?
Answer: If a length is measured by the given scale at 10°C, the reading obtained is more than the actual length.

Question 15. Why can a platinum wire be easily sealed l with glass by application of heat? 
Answer: As the coefficient of linear expansion of glass and platinum are nearly equal, a platinum wire can be easily sealed with glass by, application of heat.

Question 16. Why cannot a copper wire be sealed with glass by application of heat?
Answer: As the coefficient of linear expansion of copper is greater than that of glass, a copper wire cannot be sealed with glass by application of heat.

Question 17. Name an alloy whose coefficient of thermal expansion is much less than the same of its constituents.
Answer: Invar, an alloy with 36% nickel and 64% iron, has very low coefficient of thermal expansion compared to that of its constituent elements.

Applications of Chemical Calculations in Real Life

Question 18. A liquid is kept in a vessel whose coefficient of volume expansion is 5 x 10^-6 °C^-1. if the real coefficient of expansion of the liquid is 20 x 10^-5 °C^-1, then what is the value of apparent coefficient of expansion?
Answer: Coefficient of apparent expansion of the liquid = coefficient of real expansion of the liquid — coefficient of volume expansion of the substance of the vessel = (20 x 10^-5– 5 x 10^-6) °C^-1 = 19.5 × 10^-5 °C^-1

Question 19. A liquid is kept in two vessels A and B separately and then both are heated. The coefficient of volume expansion of the substance A is greater than that of B. The coefficient of apparent expansion of the liquid is greater in which vessel?
Answer: The coefficient of apparent expansion of the liquid is greater in the vessel B.

Question 20. A spherical metallic ball is heated. Among the radius, surface area and volume, which has the highest percentage increase?
Answer: The volume of the sphere has the highest percentage increase.

Question 21. A spherical metallic ball is heated. Among the radius, surface area and volume, which has the lowest percentage increase?
Answer: The radius of the sphere has the lowest percentage increase.

Question 22. Which coefficient of expansion of a liquid does not depend on the expansion of the container?
Answer: The coefficient of real expansion of a liquid does not depend on the expansion of the container.

Question 23. Which coefficient of expansion of a liquid depends on the expansion of the container?
Answer: The coefficient of apparent expansion of a liquid depends on the expansion of the container.

Question 24. What is the nature of the coefficient of volume expansion of a substance whose volume decreases with increase in temperature?
Answer: The coefficient of volume expansion of a substance, whose volume decreases with increase in temperature, is negative.

Question 25. The coefficient of volume expansion of water is negative in the temperature range of 0°C-4°C. Does the volume of water increase or decrease with an increase in temperature, in the given temperature range?
Answer: The volume of water decreases with an increase in temperature, in the given temperature range.

Question 26. Name one liquid substance whose coefficient of volume expansion is negative in a definite temperature range.
Answer: The value of coefficient of volume expansion of water is negative in the temperature range of 0°C-4°C.

Question 27. Name one solid substance whose coefficient of volume expansion is negative in a definite temperature range.
Answer: The value of coefficient of volume expansion of pure silicon (a solid substance) is negative in the temperature range of -153°C to -255°C.

Question 28. What is the dimensional formula of the coefficients of apparent and real expansion of a liquid?
Answer: The dimensional formula of the coefficients of apparent and real expansion of a liquid is Θ^-1.

Question 29. Define volume coefficient (γ_p) of a gas.
Answer: If the temperature of a gas is raised from 0°C to 1°C by keeping the pressure on a definite mass of gas constant, then the expansion in volume per unit volume of the gas is called the volume coefficient of that gas and it is expressed as γ_p.

Question 30. What is the unit of volume coefficient of gas?
Answer: The unit of volume coefficient of gas is °C^-1  or °F^-1 or K^-1.

Question 31. What is the dimensional formula of volume coefficient of gas?
Answer: The dimensional formula of volume coefficient of gas is Θ^-1.

Question 32. What is the value of volume coefficient of gas?
Answer: The value of volume coefficient of the gas, γ_p= 1/273 °C^-1

Question 33. Is the volume coefficient of gas different for different gases?
Answer: No, the volume coefficient of gas is the same for different gases.

Question 34. The figure 1/273 used in Charles’ law denotes the value of which coefficient of expansion?
Answer: The figure 1/273 used in Charles’ law denotes the value of the coefficient of volume expansion of gas.

Question 35. A beaker at 4°C temperature is filled with a liquid to the brim. The liquid overflows if the temperature is increased. Is the coefficient of volume expansion of the liquid positive or negative?
Answer: The coefficient of volume expansion of the liquid is positive.

Question 36. A beaker at 4°C temperature is filled with a liquid to the brim. The liquid overflows if the temperature is decreased. Is the coefficient of volume expansion of the liquid positive or negative?
Answer: The coefficient of volume expansion of the liquid is negative.

Question 37. Between the coefficients of apparent and real expansion of a liquid, which one has greater value?
Answer: The coefficient of real expansion of a liquid is greater than the coefficient of apparent expansion.

Question 38. Is it possible to construct a liquid thermometer with a glass tube if the coefficients of volume expansion of the liquid and glass are the same?
Answer: No, it is not possible because the level of liquid in the tube remains unchanged with increase in temperature.

Question 39. If value of a in Celcius and Fahrenheit scale are α_c and α_F respectively, then what is the relation between α_c and α_F?
Answer: α_c = 9/5 . α_F

Question 40. Name the substance whose length remains unchanged with the change in temperature.
Answer: Invar.

Question 41. Coefficient of apparent expansion in case of gas is not taken into account’ Why?
Answer: Because volume expansion coefficient of a gas is nearly 100 times more than that of solid.

Question 42. What do you mean by linear expansion coefficient of iron which is or = 12 x 10^-6 /°C ?
Answer: Linear expansion coefficient for iron is a = 12 x 10^-6 /°C means that an iron rod of length 1cm or 1ft or 1 m, when heated through 1°C, will expand by 12 x 10^-6 cm or 12 x 10^-6 ft or 12 x 10^-6 m respectively.

Question 43. If α_c of copper is 17.0 x 10^-6/°C, what is the volume of α_k ?
Answer: As α_c = α_k  Hence aK of copper is =17 x 10^-6 /K.

Question 44. Which one is fundamental property of a liquid-coefficient of apparent expansion or coefficient of real expansion?
Answer: Coefficient of real expansion of liquid is fundamental property of a liquid.

Question 45. What is the coefficient of linear expansion of iron if its coefficient of volume expansion is 36 x 10^-6/°C?
Answer: The coefficient of linear expansion of iron (α) = 1/3 the coefficient of linear expansion of iron (γ) = 1/3 x 36 x10^-6 = 12 x 10^-6/°c

Question 46. Mention a name of an electrical appliance in which thermostat is used.
Answer: Refrigerator.

Question 47. Among solids, liquids and gases which expands less on application of heat?
Answer: Among solids, liquids and gases solids expand less on application of heat.

Chapter 4 Phenomena Of Heat Topic A Thermal Expansion of Solid, Liquid and Gas Fill In The Blanks

Question 1. The unit of coefficient of linear expansion of any solid substance depends only on the unit of_______
Answer: Temperature

Question 2. If the coefficient of linear expansion of any solid substance in Celcius scale is 18 x 10^-6 /°C, then its value in Fahrenheit scale is ________
Answer: 10 x 10^-6 /°F

Question 3. Thermal expansion of solid is of _______ types.
Answer: Three

Question 4. Increase of length of a solid substance = ________ x coefficient of linear expansion x increase in temperature.
Answer: Initial length

Question 5. If a stopper made of brass is stuck in a bottle made of steel, the bottle has to be _________ in order to open the stopper.
Answer: Heated

Question 6. The coefficient of ________ expansion of a liquid is its inherent property.
Answer: Real

Question 7. If the coefficient of apparent expansion of a liquid is zero, then the level of liquid in a tube remains ________
Answer: Unchanged

Question 8. For accurate measurement during expansion of a gas, volume at ________ is taken as the initial volume.
Answer: 0°C

Question 9. While measuring the coefficient of volume expansion of a gas, pressure remains _________
Answer: Constant

Question 10. Coefficient of real expansion of liquid = coefficient of real expansion of container ________
Answer: Coefficient of apparent expansion

Question 11. ______ is the device which is used for automatic temperature control.
Answer: Thermostat.

Question 12. The coefficient of real expansion is an ________ property of a liquid.
Answer: Intrinsic

Question 13. On heating a bimetallic strip, made by riveting together with a strip of iron and an equal strip of brass, bends so that, the is on _______ the convex side of the curve.
Answer: Brass

Question 14. Density of liquids ________ with increase in temperature.
Answer: Decrease

Chapter 4 Phenomena Of Heat Topic A Thermal Expansion of Solid, Liquid and Gas State Whether True Or False

Question 1. The coefficient of volume expansion at constant pressure is the same for all ideal gases.
Answer: True

Question 2. The unit of coefficient of apparent expansion of a liquid depends on the unit of temperature.
Answer: True

Question 3. The unit of coefficient of real expansion of a liquid depends on the unit of volume.
Answer: False

Question 4. Thermal expansion of invar is less than that of all other metals or alloys.
Answer: True

Question 5. The thermal expansion of a liquid is generally greater than the thermal expansion of an equal volume of a solid for the same increase in temperature.
Answer: True

Question 6. The thermal expansion of a liquid is generally greater than the thermal expansion of an equal volume of a gas for the same increase in temperature.
Answer: False

Question 7. Coefficient of real expansion of water from 0°C to 4°C is positive.
Answer: False

Question 8. The value of the volume coefficient of a gas is 1/273 °C^-1
Answer: True

Question 9. The value of the pressure coefficient of a gas is 1/273 °C^-1
Answer: True

Question 10. In case .of heat conduction through a bi-metallic strip, the rate of thermal conduction for the two plates remains the same.
Answer: True

Chapter 4 Phenomena Of Heat Topic A Thermal Expansion of Solid, Liquid and Gas Numerical Examples

1. If the length of a rod at temperature t₁ is l₁ and the length becomes l₂ when the temperature is raised to t_2.

(1)Coefficient of linear expansion, \(\alpha=\frac{l_2-l_1}{l_1\left(t_2-t_1\right)}\)
(2) If the initial temperature t₁ = 0°C and the corresponding length of the rod is l₁ = l_0, then at temperature t°C length of the rod is  l_t = l₀( 1 + αt) .

2. If the value of α in Celsius and Fahrenheit scales are α_c and α_F then, α_c= 9/5 α_F

3. If the surface area of a solid at temperature t₁ is S₁ and that at temperature t₂ is S₂ then, coefficient of surface expansion, \(\beta=\frac{S_2-S_1}{S_1\left(t_2-t_1\right)}\)
(1) S_t = S₀(1 +βt)
(2) β_c = 9/5  β_F

4. If the volume of a solid at temperature t₁ is V₁  and that at temperature t₂ is V₂ then, coefficient of volume expansion, \(\gamma=\frac{V_2-V_1}{V_1\left(t_2-t_1\right)}\)

(1)V_t = V₀(1+γT)
(2)γ_c= 9/5 γ_F
(3)α = β/2 = γ/2

5. The coefficient of real expansion of a liquid (γ_r) = the coefficient of apparent expansion of a liquid (γ_a ) + the coefficient of volume expansion of the material of the container (γ_g ) . ie. γ_r = γ_a + γ_g
6. At constant pressure the volume of a fixed mass of gas at a 0°C and t°C are V₀ and V_t respectively, then V_t  = V₀ (1 + γ_pt) and, \(\gamma_p=\frac{V_t-V_0}{V_0 t}\)
∴γ_p = coefficient of  volume expansion at fixed pressure

Question 1. The lengths of an iron rod are 50 cm and 50.03 cm at 0°C and S0°C respectively. What is the value of coefficient of linear expansion of iron?

Answer: Initial temperature of iron rod (t₁) = 0°C and initial length (l₁) = 50 cm
Final temperature (t₂) = 50°C and final length (l₂) = 50.03 cm
Hence, coefficient of linear expansion of iron,

\(\alpha=\frac{l_2-l_1}{l_1\left(t_2-t_1\right)}\) or, \(\alpha=\frac{50.03-50}{50(50.0)}\) or, \(\alpha=\frac{0.03}{50 \times 50}\) or, α = 12 Χ 10^-6 °C

Question 2. The radius of a circular ring of copper is 5 cm. What is the new radius if the temperature is increased by 200°C ? Coefficient of linear expansion of brass, α =17 x 10⁶/°C

Answer: Initial radius of the ring (r₁ ) = 5 cm
Increase of temperature (t) = 200°C

Thus, final radius of the ring,  r₂= r₁( 1 + αt) or, r₂ = 5(1 + 17 x 10^-6 x 200) = 5.017cm

Question 3. The distance between two railway stations 10 km. The temperature of the place fluctuates between 10°C and 45°C in the whole year. If railway lines are to be laid in between these two stations, how much gap has to be given for safety of the line? Coefficient of linear expansion of steel, α = 12 x 10^-6/°C.

Answer: Length of rail line (L) – 10 km = 10000 m Difference between highest and lowest temperature (t) = (45 – 10)°C = 35°C
Suppose, a gap of Z has to be kept for safety of railway lines.
∴ I = L α t or, l = 10000 x 12 x 10^-6 x 35 or, l= 4.2 m .

Word Problems on Chemical Calculations with Solutions

Question 4. If the temperature of a metal sphere is increased by 50° C, its volume increases by 03%. What is the value of coefficient of volume expansion of the metal?

Answer: If the initial volume of the sphere is V, then expansion of volume = 0.3V/100 and increase in temperature = 50°C
Hence, value of coefficient of volume expansion of this metal,

\(\gamma=\frac{\frac{0.3 V}{100}}{V \times 50}\) or, γ = 60 x 10^-6/(°C)

Question 5. With reference to glass, the coefficient of volume expansion of mercury is 15.3 × 10^-5/°C. If the coefficient of volume expansion of glass is 27 x 10^-6/°C, what is the value of coefficient of real expansion of mercury?

Answer: Coefficient of apparent expansion of mercury, 15.3 × 10^-5/°C
Coefficient in volume expansion of glass, yg = 27 × 10^-6/°C = 2.7 × 10^-5/°C

∴ coefficient of real expansion of mercury,γ_r = γ_a + γ_g  or, γ_r =15.3 x 10^-5 + 2.7 x 10^-5 = 18 x 10^-5/°C

Question 6. There is 500 cm³ of mercury at 0°C in a glass vessel. If the apparent and real expansion of mercury at 100 °C are 7,65 cm³ and 9 cm³ respectively, calculate the coefficients of apparent and real expansion of mercury.

Answer:

Given

There is 500 cm³ of mercury at 0°C in a glass vessel. If the apparent and real expansion of mercury at 100 °C are 7,65 cm³ and 9 cm³ respectively,

Initial volume of iron = 500 cm³
Increase in temperature = (100-0)°C = 100°C
Apparent expansion of mercury = 7.65 cm³
Real expansion of mercury = 9 cm³

The coefficient of real expansion of mercury,

\(\gamma_a=\frac{\text { apparent expansion }}{\begin{array}{c}
\text { initial volume } \times \\
\text { increase in temperature }
\end{array}}=\frac{7.65}{500 \times 100}\) = 15.3 x 10^-5/°C

The coefficient of real expansion of mercury,

\(\gamma_r=\frac{\text { apparent expansion }}{\begin{array}{c}
\text { initial volume } \times \\
\text { increase in temperature }
\end{array}}=\frac{9}{500 \times 100}\) = 18 x 10^-5/°C

Question 7. The volume of a definite mass of a gas at . 0°C is 100 cm³ and its volume at constant pressure and 20°C is 107.33 cm³. Calculate the coefficient of volume expansion of gas.

Answer:

Given

The volume of a definite mass of a gas at . 0°C is 100 cm³ and its volume at constant pressure and 20°C is 107.33 cm³.

Volume of the gas (V₀ ) at 0°C = 100 cm³
Final temperature (t) = 20°C
Final volume (V_t) = 107.33 cm³

Hence, coefficient of volume expansion of the gas,

\(\gamma_p=\frac{V_t-V_0}{V_0 t}\) or, \(\gamma_p=\frac{107.33-100}{100 \times 20}\) or, γ_p = 3.665 x 10^-3/°C

Question 8. The volumes of a definite mass of a gas at constant pressure and at 50°C and 100°C temperature are 323 cm³ and 373cm³, respectively. Calculate the coefficient of volume expansion of the gas.

Answer:

Given

The volumes of a definite mass of a gas at constant pressure and at 50°C and 100°C temperature are 323 cm³ and 373cm³, respectively.

Suppose, volume of the gas at 0°C = V₀ and coefficient of volume expansion = γ_p
At temperature t₁ = 50°C, volume of the gas, V₁= 323 cm3.
∴ V₁ = V₀ (1 + t_1.γ_p) ……(1)

Again, at temperature t₂ = 100°C, volume of the gas, V₂= 373 cm³
∴ V₂ = V₀ (1 + γ_{p •} t2) …….(2)

If (1) is divided by (2), we get  \(\frac{V_1}{V_2}=\frac{1+\gamma_p \cdot t_1}{1+\gamma_p \cdot t_2}\)

or, \(\frac{323}{373}=\frac{1+50 \gamma_p}{1+100 \gamma_p}\)

or, 323 + 32300 γ_p = 373 + 18650 γ_p
or, 32300 γ_p – 18650yp γ_p = 373 – 323
or, 13650 γ_p = 50

or, \(\gamma_p=\frac{50}{13650}=\frac{1}{273}\)
∴ γ_p =1/273/°C

Question 9. Coefficient of apparent expansion of fmercury with respect to glass is 153 x 10^-6 °C^-1 , where coefficient of real expansion of mercury Is I8O x 10^-6 °C^-1. Find the volume expansion coefficient of glass.

Answer:

Given

Coefficient of apparent expansion of fmercury with respect to glass is 153 x 10^-6 °C^-1 , where coefficient of real expansion of mercury Is I8O x 10^-6 °C^-1.

Coefficient of real expansion of mercury (γ_r) = coefficient of apparent expansion of mercury (γ_a) + coefficient of volume expansion of glass (γ_g)

or, 180 x 10^-6 = 153 x 10^-6 + γ_g
∴ γ_g = 180X 10^-6 – 153 x 10^-6 = 27 x 10^-6
∴ Volume expansion coefficient of glass is 27 x 10^-6 °C^-1  

Visual Representation of Chemical Reactions and Calculations

Question 10. A liquid has a coefficient of apparent expansion 180 x 10^-6 °C^-1 for an iron container, and 144.6 X 10^-6°C^-1 for an aluminium container. If the coefficient of volume expansion of iron is 36 x 10^-6 °C^-1, find that of aluminium .

Answer:

Given

A liquid has a coefficient of apparent expansion 180 x 10^-6 °C^-1 for an iron container, and 144.6 × 10^-6°C^-1 for an aluminium container. If the coefficient of volume expansion of iron is 36 x 10^-6 °C^-1,

For iron container, γ = γ_a + γ_iron, symbols have usual meanings = 180 x 10^-6 + 36 x 10^-6 = 216 x10^-6

For aluminium container, γ = γ_a +γ_AI  or, 216 x 10^-6 = 144.6 x 10^-6 x γ_A,

∴ γ_AI= 216 X 10^-6– 144.6 X 10^-6 = 71.4 X 10^-6
∴ Volume expansion coefficient of aluminium is 71.4 x 10^-6 °C^-1 .

Question 11. The internal volume of a glass flask is V cm³  . What volume of mercury should be kept in the flask so that the volume of the empty space remains constant at any temperature? Real expansion of mercury r= 180 x 10^-6 °C^-1 and volume expansion of glass =25 x 10^-6 °C^-1 .

Answer: Let, the volume of mercury be x cm³  .

To keep the volume of the empty space constant at any temperature, the expansion of mercury should be equal to that of the glass flask for the same rise in temperature. If the temperature rise is t°C,then x x 180 x 10^-6 x t = V x 25 x 10^-6 x t or Χ = 25V/180 = 5/36 V
∴ 5/36 V cm³  of mercury should be kept in the flask.

Chapter 4 Phenomena Of Heat Topic B Thermal Conductivity Synopsis

1. Flow of heat from one place to another is called transmission of heat.
2. Heat is transmitted in three different process—conduction, convection and radiation. .
3. The process in which heat flows from a higher temperature region to a lower temperature region of a material without any displacement of material particles is called conduction.

4. Materials which can conduct heat easily are called thermal conductors.
5. Materials which cannot conduct heat easily are called bad conductor of heat or thermal insulators. Fibre glass, paper, cork, water, wood, glass etc are bad conductors of heat.

6. During transmission of heat through any object if both conduction and absorption go on simultaneously, it is called pre-steady state condition of heating.
7. In pre steady state heat conduction through a rod depends on both 0 the coefficient of thermal conductivity and specific heat of the material of the rod.
8. In steady state only conduction of heat takes place not absorption.

9. In steady state heat conduction along a rod depends only on the coefficient of thermal conductivity of its material. The coefficient of thermal conductivity of material is defined as the quantity of heat that conducts per unit time through unit area of the material keeping its opposite faces at a temperature difference of one degree, when the steady state has been reached.

Let a rectangular plate of cross sectional area A and thickness d maintain temperatures θ₁ and θ₂ on its two opposite faces where θ₁>θ₂ . in this condition heat passes perpendicularly through the slab from the hotter surface to the colder surface. If θ amount of heat is transferred perpendicularly across the plate in time t in steady state then it is observed experimentally that,

1. Q is directly proportional to A i.e., Q ∝ A
2. Q is directly proportional to (θ₁ – θ₂) i.e., Q ∝ (θ₁ – θ₂)
3. Q is directly proportional to t, i.e., Q ∝ t
4. Q is inversely proportional to d i.e., Q α 1/d

Hence,\(Q \propto \frac{A\left(\theta_1-\theta_2\right) t}{d}\)

or, \(Q=k \cdot \frac{A\left(\theta_1-\theta_2\right) t}{d}\) k is a constant

The value of the constant depends on the material of the plate. k is known as the coefficient of thermal conductivity.

10. For ideal conductor k is infinity and for an ideal insulator k= 0.

Wbbse Class 10 Physical Science Chapter 4 Question Answer

Units of k: In CGS system, \(calorie $\cdot \mathrm{cm}$
$\mathrm{cm}^2 \cdot{ }^{\circ} \mathrm{C} \cdot$ second\) = cal. cm^-1. °C^-1.s^{-1 .}

In SI it is J. m^-1 . K^-1 . s^-1= W . m^-1 . K^-1

We know that, \(k=\frac{Q \cdot d}{A\left(\theta_1-\theta_2\right) t}\)

∴ Dimensional formula of k, \(=[k]=\frac{\mathrm{ML}^2 \mathrm{~T}^{-2} \times \mathrm{L}}{\mathrm{L}^2 \cdot \Theta \times \mathrm{T}}\) = \(=\mathrm{MLT}^{-3} \Theta^{-1}\)

12. Silver have highest thermal conductivity among metals [k = 406 SI unit)
13. Diamond is the best thermal conductor {k^ 1000 SI unit)
14. Among liquids, mercury is the best conductor {k = 8.3 SI unit)
15. Thermal conductivity of vacuum is zero.

16. Thermal resistance is defined as the property of a substance by which it resists the flow of heat through it.

Electrical resistance (R) = \(=\frac{\text { potential difference }\left(V_1-V_2\right)}{\text { intensity of electric current }(I)}\)

Thermal resistance = \(=\frac{\text { temperature difference }\left(\theta_1-\theta_2\right)}{\text { heat current }(H)}\) = \(=\frac{\left(\theta_1-\theta_2\right)}{Q / t}\)

[Heat current (H) = flow of heat (Q)/ time (t)]

From the relation of k we get, \(Q=\frac{k \cdot A\left(\theta_1-\theta_2\right) t}{d}\) ,\(\text { or, } \frac{\left(\theta_1-\theta_2\right)}{Q / t}=\frac{d}{k \cdot A}\)

Electrical resistance,\(R=\rho \cdot \frac{l}{A}\) [p = resistivity, l = length, A = area of cross section]

So, 1/k is similar to p
Hence 1/k is called thermal Resistivity.

17. Similarities between heat conduction and electrical conduction:

18. Dissimilarities between heat conduction and electrical conduction:

Chapter 4 Phenomena Of Heat Topic B Thermal Conductivity Short And Long Answer Type Questions

Question 1. What is conduction? Write down the characteristics of transmission of heat in the process of conduction.

Answer:

Conduction

It is the method in which heat is transmitted from a warmer place of the substance to a colder place without any displacement of the molecules.

In the conduction process:
1. A solid medium is required for heat transmission.
2. The medium becomes hot during heat transmission.
3. There is no displacement of the molecules of the medium at the time of heat transmission.
4. Heat can be transmitted along any of straight or curved path.

Question 2. What do you mean by pre-steady state condition in case of conduction of heat? Demonstrate with the help of an experiment that the capacity of heat conduction is different for different substances.

Answer:

Pre-steady state condition in case of conduction of heat

During transmission of heat through any object if both conduction and absorption go on simultaneously, it is called pre-steady state condition of heating.

Experiment: A rectangular, metallic vessel is taken. Three holes are made on its wall in the same height. Three different metal rods (say of copper, aluminium and iron) of same length and same cross sectional area are inserted through the holes. The portion of the rods outside the vessel are wax-coated.

Next, water is poured in the vessel and then it is heated uniformly by a bunsen burner. In this condition heat conducts along the lengths of the rods. After some time, it is seen that wax has melted in all the rods but up to different lengths.

Conclusion: It is clearly understood from this experiment that the capacity of conducting heat is different for different substances. If wax melts up to l₁, l₂ and l₃ on copper, aluminium and iron rods respectively, it is observed that l₁ > l₂ > l₃

Understanding the Concept of Limiting Reactants

Question 3. What is thermal conductivity? Suppose the thickness of a rectangular plate is d, its cross-sectional area is A and the temperature of its opposite sides are θ₁ and θ₂ respectively (where θ₁ > θ₂). At thermal steady state, if Q amount of heat is transmitted perpendicularly in time t from the hotter side to the colder side then how can you express thermal conductivity of the substance of the plate?

Answer:

Thermal conductivity

The thermal conductivity of a substance is defined as the heat conducted perpendicularly in one second across the opposite faces of a cuboid of unit cross-sectional area and unit thickness when the difference in temperature of its two opposite faces is unity.

By experiment, it has been seen that:

1. Q ∝ A
2. Q∝(θ₁-θ₂)
3. Q ∝1/d
4. Q ∝ t

According to the rule of compound variation, \(Q \propto \frac{A\left(\theta_1-\theta_2\right) t}{d}\) or, \(Q=\frac{k A\left(\theta_1-\theta_2\right) t}{d}\)

∴ \(k=\frac{Q \cdot d}{A\left(\theta_1-\theta_2\right) t}\)

where k is a constant, known as the thermal conductivity of the substance of the plate.

Question 4. Find out the unit of thermal conductivity. Establish a relationship between the units thermal conductivity in CGS system and SI.

Answer: From definition, we have thermal conductivity, K = Q . d/Aθt
Where d= thickness, A= cross-section area, = temperature difference, t= time and Q = heat.

So,unit of k(in SI) = \(=\frac{J \times m}{m^2 \times K \times s}\) = J . m^{-1 .}  K^{-1 .} s^-1    and in CGS it is cal.cm^{-1 .}  K^{-1 .} s^-1

1 cal.cm^-1.  C^{-1 .} s^-1= 42J. (10^-2m)^-1 K^{-1 .} s^-1  = 420W.m^-1.  K^{-1 .} 

Question 5.  What do you mean by thermal resistance? What is the unit of thermal resistance?

Answer:

Thermal resistance

Thermal resistance is defined as the property of a substance by which it resists the flow of heat through it.

Let the thickness of a body be d, its cross-sectional area be A and the thermal conductivity of its substance be k.

Therefore, its thermal resistance is d/kA.
Thermal resistance, = \(\frac{d}{k A}=\frac{\theta_2-\theta_1}{Q / t}=\frac{\left(\theta_2-\theta_1\right) t}{Q}\)

Now, unit of (θ₂-θ₁) is kelvin (K), unit of t is second (s), unit of Q is the joule (J). Hence, unit of thermal resistance is K. s. J-¹.

Question 6. How is the thermal resistance of a conductor compared with its electrical resistance?

Answer: The cause of an electric current(l) through a conductor is the potential difference(V) between its two ends.

According to Ohm’s law V= IR or, \(R=\frac{V}{l}=\frac{V}{\left(\frac{q}{t}\right)}\)…….(1)

Similarly, the cause of conduction of heat through a conductor is the difference of temperature at the two ends of the conductor(θ).

Thus, amount of heat conducted, \(Q=k \cdot A \frac{\theta}{d} \cdot t\) or \(\frac{d}{k A}=\frac{\theta}{\left(\frac{Q}{t}\right)}\) …..(2)

There is somewhat similarity between equation (1) and equation(2). In this way, the quantity(d/kA) is similar to R. Thius is the thermal resistance of a conductor.

Question 7. I = q/t = V/R and \(\frac{Q}{t}=k \cdot A \cdot \frac{\left(\theta_2-\theta_1\right)}{d}\)
What are the similarities between different quantities in these two equations? [The symbols represent conventional physical quantities]

Answer:

The similarities in the two equations are shown:

Type	Electrical quantities	Quantity related to heat conduction
Quantity	Electrical charge (q)	Heat (Q)
Property	Potential difference (V)	Difference of temperature (θ2 – θ1  )
Rate of flow	Current ( I = q/t)	Rate of conduction of heat (Q/t)
Resistance	Electrical resistance (R)	Thermal resistance (d/kA)

Question 8. Define conductor and insulator of heat. Why is the handle of a kettle wrapped with cane?

Answer:

Conductor and insulator of heat.

1. Conductors of heat are those substances through which heat can be conducted easily. For example, iron.
2. Insulators of heat are those substances through which heat cannot be conducted easily. For example, wood.

3. Kettle is generally made of aluminium. Aluminium is a good conductor of heat. When water or any other liquid is heated in a kettle, the kettle also becomes hot along with the liquid inside it. In this condition, it is Very difficult to touch the handle of the kettle. Cane is an insulator of heat. So, if cane is wrapped on the handle of the kettle, no heat is transmitted to the hand and the handle can be touched easily. For this reason, the handle of a kettle is wrapped with a cane.

Question 9. If we touch two chairs, one of wood and the other of iron, both at the same temperature during winter, why does the iron chair feel colder than the other? In which condition they feel same in temperature?

Answer:
1. Our body temperature generally remains higher than the temperature of a chair during winter. Wood is a bad conductor of heat but iron is a good conductor of heat. If we touch an iron chair, heat is transmitted very quickly from our body to the chair but when we touch a wooden chair, conduction of heat is very slow.

2. This is why the iron chair feels colder. As the temperature of the chair becomes equal with one’s body temperature, they feel same in temperature.

Wbbse Class 10 Physical Science Chapter 4 Question Answer

Question 10. Let us take a rod, half of which is made of wood and the other half is made of copper; The rod is wrapped with a thin paper. Now it is held directly over the flame of a burner. Explain what happens.

Answer: If the rod is held directly over the flame of a burner, it is seen that the paper surrounding the wooden portion is burnt immediately but the paper surrounding the copper side is not burnt. Copper being a good conductor .of heat, heat is conducted evenly all over the rod and the temperature of the paper does not reach the ignition point.

But in the case of wood which is a bad conductor of heat, heat is not conducted. As a result, the temperature reaches the ignition point and the paper is burnt. But if held for a long time, the paper on the copper part also gets burnt.

Question 11. Why the birds fluff up their feathers during winter?

Answer: During winter the birds fluff up their feathers to keep themselves warm. When the birds fluff up their feathers, feathers trap air in them. As air being an insulator, does not allow heat from the body to escape. So the birds keep warm.

Question 12. Wearing of two relatively fiver clothes instead of a thick cloth is more comfortable. Why?

Answer:

Wearing of two relatively fiver clothes instead of a thick cloth is more comfortable.

If we wear two relatively fiver clothes instead of a thick cloth, we feel warmer. This happens because the two clothes trap a layer of air between them. Air is a thermal insulator and so it prevents the heat from our body from escaping. So we feel warm and more comfortable.

Chapter 4 Phenomena Of Heat Topic B Thermal Conductivity Very Short Answer Type Questions Choose The Correct Answer

Question 1. Which of the following metals has the highest conductivity?

1. Copper
2. Aluminium
3. Silver
4. Gold

Answer: 3. Silver

Question 2. The value of thermal conductivity of an ideal conductor (in the unit of cal • cm^{-1. °}C^{-1 .} s^-1) is

1. 0
2. 1
3. 100
4. ∞

Answer: 4. ∞

Question 3. The value of thermal conductivity of an ideal insulator (in the unit of cal • cm^-1 • °C^-1  • s^-1) is

1. 0
2. 1
3. 100
4. ∞

Answer: 1. 0

Question 4. At steady state,

1. Both conduction and absorption of heat take place
2. Neither conduction nor absorption of heat takes place
3. Only absorption of heat takes place, not conduction
4. Only conduction of heat takes place, not absorption

Answer: 4. Only conduction of heat takes place, not absorption

Question 5. The value of the thermal conductivity of a substance is 42 W • m^-1  K^-1. What is its value in CGS unit?

1. 0.1
2. 0.12
3. 0.13
4. 0.15

Answer: 1. 0.1

Question 6. Dimensional formula of thermal resistance is

1. M^-1L^-2T^-3 Θ^-1
   
2. M^-1L^-3T³ Θ
3. ML^-2T³ Θ
4. M^-1L^-2T³ Θ

Answer: 4. M^-1L^-2T³ Θ

Question 7. What is the power of L in the dimensional formula of thermal conductivity?

1. 1
2. 2
3. -1
4. -2

Answer: 1. 1

Question 8. Diamond is

1. Good conductor of heat and electricity
2. Bad conductor of heat and electricity
3. Bad conductor of heat, good conductor of electricity
4. Good conductor of heat, bad conductor of electricity

Answer: 4. Good conductor of heat, bad conductor of electricity

Question 9. Which of the following is a good conductor of heat?

1. Cork
2. Air
3. Wood
4. Graphite

Answer: 4. Graphite

Question 10. A rectangular plate has thickness = d, cross sectional area = A and thermal conductivity = k. What is the value of thermal resistance?

1. d/kA
2. kA/d
3. dA/k
4. A/kd

Answer: 1. d/kA

Question 11. What is the increase in area of a substance if the coefficient of its surface expansion = 2 x 10^-5°C^-1, initial area = 104 cm² and increase of temperature = 100°C?

1. 21 cm² 
2. 20 cm² 
3. 22 cm²
4. 23 cm² 

Answer: 2. 20 cm² 

Question 12. In which case the thermal conductivity increases from left to right?

1. Al, Cu, Ag
2. Ag, Cu, Al
3. Cu, Ag, Al
4. Al, Ag, Cu

Answer: 1. Al, Cu, Ag

Question 13. For cooking food, which of the following type of utensil is most suitable?

1. High specific heat and high conductivity
2. Low conductivity
3. Low specific heat and low conductivity
4. Low specific heat and high conductivity

Answer: 4. Low specific heat and high conductivity

Question 14. Under steady state, the temperature of a body

1. Increases with time
2. Decreases with time
3. Does not change with time and is same at all the points of the body
4. Does not change with time but different at different points of the body

Answer: 4. Does not change with time but different at different points of the body

Question 15. Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minute and 30 minutes respectively. The ratio of their thermal conductivity will be

1. 3:2
2. 1:1
3. 2:3
4. 4:1

Answer: 1. 3:2

Question 16. The coefficient of thermal conductivity depends upon

1. Temperature difference of two surfaces
2. Area of the plate
3. Thickness of the plate
4. Material of the plate

Answer: 4. Material of the plate

Wbbse Class 10 Physical Science Chapter 4 Question Answer

Question 17. A piece of metal appears colder in winter morning than a piece of wood when touched because

1. Metal has high specific heat
2. Metal has high thermal conductivity
3. Metal has low specific heat
4. Metal has low thermal conductivity

Answer: 2. Metal has high thermal conductivity

Question 18. On heating one end of a rod, the temperature of whole rod will be uniform when,

1. k=1
2. k = 0
3. k = very small
4. k = infinity

Answer: 4. k = infinity

Question 19. Mud houses are cooler in summer and Warmer in winter because

1. Mud is a good conductor of heat
2. Mud is a bad conductor of heat
3. Thermal conductivity of mud is infinite
4. Thermal conductivity of mud is 0

Answer: 2. Mud is a bad conductor of heat

Question 20. If thermal conductivity of a material is k, then it’s thermal resistivity is

1. k
2. 1/k
3. k²
4. 1/k²

Answer: 2. 1/k

Chapter 4 Phenomena Of Heat Topic B Thermal Conductivity Answer In Brief

Question 1. Name one liquid which is a good conductor of heat.
Answer: Mercury is a liquid which is a good conductor of heat.

Question 2. Name one substance whose electrical conductivity is very low but whose thermal conductivity is very high.
Answer: Diamond has very low electrical conductivity but very high thermal conductivity.

Question 3. What is the value of the thermal conductivity of a diamond?
Answer: The value of thermal conductivity of a diamond is 5.2380 cal • cm^-1. s^-1. K^-1    or, 22 W . cm^-1. K^-1 (approx.).

Question 4. Name the substance with the highest thermal conductivity at room temperature.
Answer: According to the latest available information, monocrystalline synthetic diamond has the highest thermal conductivity at room temperature.

Question 5. What is the thermal conductivity of monocrystalline synthetic diamond at room temperature?
Answer: The thermal conductivity of monocrystalline synthetic diamond at room temperature is 33.2 W • cm^-1. K^-1 (approx.).

Question 6. State whether diamond or copper has the higher value of thermal conductivity.
The thermal conductivity of diamond is approximately five times more than that of copper.

Question 7. What is the dimensional formula for thermal conductivity?
Answer: Dimensional formula for thermal conductivity is MLT^-3Θ^-1.

Question 8. What is the unit of thermal conductivity in CGS system?
Answer: Unit of thermal conductivity in CGS system is cal.cm^-1. °C^-1.s^-1 .

Question 9. What is the unit of thermal conductivity in SI?
Answer: Unit of thermal conductivity in SI is W • m^-1 • K^-1.

Question 10. When is the value of the thermal resistance of a substance equal to the reciprocal of its thermal conductivity?
Answer: The value of the thermal resistance of a substance is equal to the reciprocal of its thermal conductivity when its thickness is equal to its cross sectional area.

Question 11. By keeping the length (thickness) of a slab unchanged, if its area of cross section is halved, how many times does its thermal resistance increase?
Answer: By keeping the length (thickness) of a slab unchanged, if its area of cross section is halved, its thermal resistance increases two times.

Question 12. By keeping the area of cross section of a slab unchanged, if the length (thickness) is halved, how many times does its thermal resistance increase?
Answer: By keeping the area of cross section of a slab unchanged, if its length (thickness) is halved, its thermal resistance is also halved.

Question 13. If the thermal conductivity of a substance is k = 0.8 cal • cm^-1. °C^-1. s^-1, what is the value of k in SI?
Answer: The value of thermal conductivity k in SI is 0.8 X 420 W • m^-1 • K^-1 = 336 W • m^-1 • K^-1.

Question 14. When do we feel an iron chair and a wooden chair to be hot to the same extent, by touching?
Answer: We feel the two chairs to be hot to the same extent, when the body temperature and the temperatures of the two chairs become equal.

Wbbse Class 10 Physical Science Chapter 4 Question Answer

Question 15. What are thermal conductors of heat?
Answer:

Thermal conductors of heat

Materials which can conduct heat easily are called thermal conductors of heat.

Question 16. What are insulators or bad conductors of heat?
Answer: Materials which can not conduct heat easily are called insulators or bad conductors of heat.

Question 17. Thickness and area of cross section of a rectangular metallic plate are d and A respectively. Thermal conductivity of the material of the plate is k. What is its thermal resistance?
Answer: Thermal resistance of the plate is d/kA.

Question 18. If thickness and area of cross section of a metallic plate are unchanged then what will be the relation between thermal resistance and thermal conductivity?
Answer: If thickness and area of cross section of a rectangular slab are unchanged then thermal resistance (R) is inversely proportional to the thermal conductivity.

Question 19. If thermal conductivity is k then which physical quantity is denoted by 1/k?
Answer: 1/k denotes the thermal resistivity.

Question 20. Keeping area of cross section of a rectangular slab unchanged, if thickness of the slab is 1/2 of its initial value, then what 2 will be the change in its thermal resistance?
Answer: Thermal resistance will be 1/2 of its initial value.

Question 21. What is the value of thermal conductivity of vacuum?
Answer: The thermal conductivity of vacuum is zero.

Question 22. What is the value of thermal conductivity of an ideal insulator of heat?
Answer: The value of thermal conductivity of an ideal insulator of heat is zero.

Question 23. What is the value of thermal conductivity of an ideal conductor of heat?
Answer: The value of thermal conductivity of an ideal conductor is infinite.

Question 24. In which state of conduction of heat through solids no heat is absorbed by any layer of the solid?
Answer: In steady state there is no absorption of heat by any layer of a solid.

Question 25. In which state of conduction of heat through solids heat is absorbed by different layers of a solid?
Answer: In pre-steady state of conduction of heat through solids some amount of heat is absorbed by the different layers of the solid.

Chapter 4 Phenomena Of Heat Topic B Thermal Conductivity Fill In The Blanks

Question 1. There is _______displacement of the molecules of the medium during transmission of heat by the conduction process.
Answer: No

Question 2. Thermal conductance of wooden dust is_____ than that of wood.
Answer: Less

Question 3. Thermal conductivity of vacuum is _______
Answer: Zero

Question 4. The value of thermal conductivity of diamond is _______ than that of gold.
Answer: More

Wb Class 10 Physical Science Solutions

Question 5. If the value of thermal conductivity is more, thermal resistance is _______
Answer: Less

Question 6. From _______ experiment it was proved that thermal conductivity of different materials are different.
Answer: Ingenhousz

Question 7. SI unit of thermal resistance is _______
Answer: K/watt

Question 8. Flow of heat from one place to another is called _______ of heat.
Answer: Transmission

Question 9. Conduction usually takes place in ______
Answer: Solids

Question 10. All gases are _____ conductors of heat.
Answer: Bad

Question 11. vacuum can not conduct heat and therefore it is an _______ insulator.
Answer: Ideal

Question 12. Rate of flow of heat is called ______ current.
Answer: Heat

Question 13. The reciprocal of coefficient of thermal conductivity is ______ of the conductor.
Answer: Thermal Resistivity

Question 14. Material medium is necessary for transmission of heat in the process of _____
Answer: Conduction

Question 15. In the process of ______ of heat, heat can travel along a straight or a curved path.
Answer: Conduction

Chapter 4 Phenomena Of Heat Topic B Thermal Conductivity State Whether True Or False

Question 1. The coefficient of thermal conductivity of a conductor does not depend on the substance of the conductor.
Answer: False

Question 2. All metals are bad conductors of heat.
Answer: False

Question 3. The rate of thermal conduction remains the same if the temperature difference between the two ends of a conducting rod is made twice the previous value.
Answer: False

Question 4. Material medium is necessary for conduction of heat.
Answer: True

Question 5. During conduction of heat through solids, molecules of the solid can move freely.
Answer: False

Question 6. Vacuum is an ideal conductor of heat.
Answer: False

Question 7. Thermal conductivity of diamond is less than that of silver.
Answer: False

Question 8. Silver is the best metallic conductor of heat.
Answer: True

Question 9. Thermal conductivity is the property of a material that, indicates its ability to conduct heat.
Answer: True

Chapter 4 Phenomena Of Heat Topic B Thermal Conductivity Numerical Examples

1. If the temperatures of the two faces of a rectangular plate of cross sectional area A and of thickness d be θ₁ and θ₂ (θ₁ > θ₂) then the amount of heat conducted in time t from the hot to the cold face of the plate will be,

\(Q=\frac{k A\left(\theta_1-\theta_2\right) t}{d}\)

2. Heat current = \(\frac{Q}{t}=\frac{k A\left(\theta_1-\theta_2\right)}{d}\)

3. Temperature gradient = \(\frac{\theta_1-\theta_2}{d}\)

4. Thermal resistance of a conductor = \(\frac{1}{k} \cdot \frac{d}{A}\)

5. Thermal resistivity of a conductor = 1/k

Wb Class 10 Physical Science Solutions

Question 1. Thickness, surface area and thermal conductivity of two rods are in the ratio 1: 2 . What is the ratio of thermal resistance of the two rods?

Answer:

Given:

Thickness, surface area and thermal conductivity of two rods are in the ratio 1: 2 .

Suppose, thickness, cross sectional area and thermal conductivity of two rods are d₁, d₂: A₁, A₂ and k₁, k₂ respectively.

∴ \(\frac{d_1}{d_2}=\frac{A_1}{A_2}=\frac{k_1}{k_2}=\frac{1}{2}\)

Thermal resistance of the first rod, \(R_1=\frac{d_1}{k_1 A_1}\) and thermal resistance of the second rod, \(R_2=\frac{d_2}{k_2 A_2}\)

∴ \(\frac{R_1}{R_2}=\frac{d_1}{k_1 A_1} \times \frac{k_2 A_2}{d_2}\) or, \(\frac{R_1}{R_2}=\frac{d_1}{d_2} \times \frac{k_2}{k_1} \times \frac{A_2}{A_1}\) or, \(\frac{R_1}{R_2}=\frac{1}{2} \times 2 \times 2\) or, \(\frac{R_1}{R_2}=2\)

Therefore, the ratio of thermal resistance of the two rods is R₁: R₂ = 2:1

Question 2. A and B are two rods of the same length. For each of them, temperature on two sides are T₁°C and T₂°C(T₁> T₂) respectively. Which condition has to be fulfilled in order to have the same rate of transmission of heat through both the rods?

Answer:

Given:

A and B are two rods of the same length. For each of them, temperature on two sides are T₁°C and T₂°C(T₁> T₂) respectively.

Suppose, length of each rod = l, thermal conductivities are k₁ and k₂ respectively and cross sectional areas are A₁  and A₂ respectively. Rate of transmission of heat through both rods are equal.

∴ \(\frac{k_1 A_1\left(T_1-T_2\right)}{1}=\frac{K_2 A_2\left(T_1-T_2\right)}{l}\) or, k₁A₁  = k₂A₂

Therefore, the condition k₁A₁  = k₂A₂ has to be fulfilled in order to have the same rate of transmission of heat through them.

Question 3. The rate of transmission of heat through a rod is 6000 J/s. Its length and cross sectional area are 1m and 0.5 m² respectively. If the thermal conductivity of the rod is k = 200W•m^-1K^-1, what is the difference of temperature between the two sides?

Answer:

Given:

The rate of transmission of heat through a rod is 6000 J/s. Its length and cross sectional area are 1m and 0.5 m² respectively. If the thermal conductivity of the rod is k = 200W•m^-1K^-1,

Length of the rod (d) = lm
Cross sectional area (A) = 0.5 m²
Rate of transmission of heat through the rod(Q/t) =6000 J/s
Suppose, temperature difference between the two sides of the rod = θ°C

∴ \(\frac{Q}{t}=\frac{k A \theta}{d}\) or, \(6000=\frac{200 \times 0.5 \times \theta}{1}\) or, 100θ=6000 or, θ = 60°C

Wb Class 10 Physical Science Solutions

Question 4. Window has an area of 3 m² and thickness of glass of 2 mm . Temperature at the inside and outside of the glass surface are 20°C and -5°C, respectively. What amount of heat is transmitted through the windows to the outside per minubte due to conduction? Thermal conductivity of glass is 0.002 CGS unit.

Answer:

Given:

Window has an area of 3 m² and thickness of glass of 2 mm . Temperature at the inside and outside of the glass surface are 20°C and -5°C, respectively.

Here, k = 0.002 CGS unit A = 3 m²= 3 x 104cm², θ = 2O°C, θ = -5°C, t = 60 s, d = 2 mm = 0.2 cm

We know, \(\mathrm{Q}=\frac{k A\left(\theta_2-\theta_1\right) t}{d}\) = \(\frac{0.002 \times 3 \times 10^4\{20-(-5)\} \times 60}{0.2}\) = 45 104cal

Therefore, an amount of heat of 45x 10⁴ cal is transmitted from the room through each window.
Hence, 2 x 45 x10⁴ caI= 90 x10⁴ cal of heat is transmitted through the two windows.

Question 5. The area of cross section of a metallic rod of length 20 cm is 2 cm². If coefficient of thermal conductivity of the material of the rod is k=0.5 cal. cm^-1 • °C^-1 • s^-1   then find its thermal resistance.

Answer:

Given:

The area of cross section of a metallic rod of length 20 cm is 2 cm². If coefficient of thermal conductivity of the material of the rod is k=0.5 cal. cm^-1 • °C^-1 • s^-1  

Length of the rod (d) = 20 cm, area of cross section of the metallic rod (a) = 2 cm²

∴ Thermal resistance of the rod \(R_T=\frac{d}{k A}=\frac{20}{0.5 \times 2}\) = 20°C^-1 • s • cal^-1

Question 6. Two opposite surfaces of a cuboid of volume 1000 cm³ are kept in contact with steam at 100°C and ice at 0°C respectively. The coefficient of thermal conductivity of the material of the cuboid k = 0.5 cal. cm^-1 • °C^-1 • s^-1 and latent heat of melting of ice = 80 cal/g. What mass of ice will melt in time 8 min?

Answer:

Given:

Two opposite surfaces of a cuboid of volume 1000 cm³ are kept in contact with steam at 100°C and ice at 0°C respectively. The coefficient of thermal conductivity of the material of the cuboid k = 0.5 cal. cm^-1 • °C^-1 • s^-1 and latent heat of melting of ice = 80 cal/g.

Length of a each side of the cuboid (l) = \(\sqrt[3]{100}\) = 10cm

∴ Area of each surface of the cuboid (A) = (10)² = 100 cm²
Temperature difference between two opposite surfaces (θ₁– θ₂ ) = (100 – 0)°C = 100°C
Coefficient of thermal conductivity of the material (k) = 0.5 cal. cm^-1 • °C^-1 • s^-1

Time for conduction of heat (t) = 8 min = 8 x 60 = 480 s
Latent heat of melting of ice (Z.) = 80 cal/g

If, m g ice melts, then, according to the problem, \(m \cdot L=\frac{k \cdot A\left(\theta_1-\theta_2\right) t}{d}\)

or,\(m \cdot 80=\frac{0.5 \times 100(100-0) \cdot 480}{10}\)

or, \(m=\frac{0.5 \times 100 \times 100 \times 480}{80 \times 10}=3000\)

∴ 3000g or 3kg ice will melt.

Question 7. room has a glass window of area 1 m² and thickness 0.5 cm. The inside and the outside temperature of the room are 10°C and 40°C respectively. Find the amount of heat conducted in 10 min through the window if k of the glass is = 0.0012 cal. cm^-1 • °C^-1 • s^-1

Answer:

Given:

Room has a glass window of area 1 m² and thickness 0.5 cm. The inside and the outside temperature of the room are 10°C and 40°C respectively.

Thickness of the glass (d) = 0.5 cm , area of the glass window (A) = 1m² = 10⁴ cm², temperature difference (θ₁ -θ₂) = (40 – 10) = 30°C, time (f) = 10 min = 10 x 60 s = 600 s .

∴ The amount of heat transmitted through the glass window, \(Q=\frac{k A\left(\theta_2-\theta_1\right) \cdot t}{d}\) = \(m=\frac{0.5 \times 100 \times 100 \times 480}{80 \times 10}=3000\) = 4.32 x 10⁵cal

Chapter 4 Phenomena Of Heat Miscellaneous Type Questions Match The Columns

Question 1.

Column A	Column B
Unit of coefficient of apparent expansion of a liquid	1. M-1L-2T3
Unit of thermal conductivity	2. K-1
Dimensional formula of thermal resistance	3. MLT-3Θ-1
Dimensional formula of thermal conductivity	4. W m-1 K-1

Answer:
Unit of coefficient of apparent expansion of a liquid: 2. K^-1
Unit of thermal conductivity: 4. W m^-1 K^-1 
Dimensional formula of thermal resistance: 1. M^-1L^-2T³
Dimensional formula of thermal conductivity: 3. MLT^-3Θ^-1

Question 2.

Column A	Column B
The metal which has the highest thermal conductivity	1. Water
A liquid which is a good conductor of heat	2. Wood
A substance which has a high thermal resistivity	3. Mercury
A liquid which displays the anomalous expansion	4. Silver

Answer:
The metal which has the highest thermal conductivity: 4. Silver
A liquid which is a good conductor of heat: 3. Mercury
A substance which has a high thermal resistivity: 2. Wood
A liquid which displays the anomalous expansion: 1. Water

WBBSE Solutions for Class 10 Physical Science and Environment