NEET Foundation

Chapter 4 Why Do We Fall Ill

We all are aware of the fact that the cell is the basic structural and functional unit of life. Every cell is made up of various biomolecules like proteins, carbohydrates, lipids and nucleic acids. The cells are found in the dynamic state even in the condition when the cell is immobile, other functions like cell repair and the formation of new  cells may take place continuously.

Any kind of improper functioning of these biomolecules will lead to health disorders and subsequently, multiple diseases. You must have heard about people talking about good and bad health.

Read and Learn More: NEET Foundation Notes

How can we define ‘health’ and ‘disease’? In the recent  past, one of the most important things that man has realized is that numerous diseases can be prevented by taking simple preventive  measures that include proper sewage system, safe drinking water,  clean air and surrounding, and personal hygiene. The result of this  activity reveals that health and diseases are interconnected, where ill  health may lead to acquire several diseases.

Chapter 4 Why Do We Fall Ill Health And Its Failure

The Significance of Health

Health depicts the notion of well-being. The meaning of good health may vary from person to person such as for a person working in coal mine, it refers to being fit to perform hard labour while at the same time a person working in office, it may refer to the mental fitness to take wise decisions.

Therefore, the term ’health’ can be defined as the state of complete physical, social and mental well-being. Being healthy does not merely stand for being free from disease. The World Health Organization defines health as a state of complete physical, mental and social wellbeing and not merely the absence of disease or infirmity.

However, maintaining good hygiene reduces the probability of accumulating disease. It reflects the ability of a person to feel good, have a positive outlook and to cope up with day-to-day activities without much difficulty.

The health of a person and community are interrelated. However, there are ­certain basic factors necessary to maintain the health of an individual such as personal hygiene, balanced diet, clean surroundings, proper exercise, good economic conditions, etc.

NEET Foundation Notes For Biology Chapter 4

The three fundamental elements of health are discussed below.

• Physical element: It deals with the body’s ability to partake in exercise, proper nutrition, enough sleep, weight management, abstinence from alcohol and drugs.
• Social health: It deals with the way we react with people in our environment and it includes public, peer and family relationship.
• Mental health: It deals with how we feel, think and manage with life.

Personal and Community Issues Both Matter for Health

The health of all organisms depends on its surroundings and the environment where they live. Besides that we live in villages, towns and cities, our socio-economic environment also plays a crucial role in determining our health.

Consider a situation where there is no agency to ensure proper collection and disposal of waste. What would happen if the drains are not cleaned regularly? Imagine yourself living in a place surrounded by a great deal of garbage thrown on streets with open drain and water being stagnant.

The possibility of developing poor health in such cases increases. Therefore, public cleanliness along with proper hygiene and sanitation is also an important factor to maintain an individual’s health.

Conditions Essential to Maintain Good Health

• Proper sanitation
• Availability of clean drinking water
• Availability of sufficient and nutritious food
• Social equality

Distinction between Healthy and Diseases-Free 

Health is a dynamic state of well-being involving physical, mental and social domains which satisfies the demands of a life that is associated to age, culture, personal responsibilities. The term ‘disease-free’ describes a condition of well-being where one is not suffering from any disease, but cannot be considered as healthy.

Sometimes the body may function efficiently, but it is not compulsory that they are mentally and socially stable and active. Thus, ‘Not being diseased’ is not the same as being ‘healthy’ and we can be in poor health without a simple cause in the form of identifiable disease.

Difference between healthy and disease-free person

Chapter 4 Why Do We Fall Ill Disease And Its Causes

Each organ system in our body has a specific role to perform. The malfunctioning of any of these organs and organ system is characterized by various signs and symptoms, where it indicates the presence of a disease.

Disease

Disease is defined as an abnormal condition that disturbs or modifies the performance of the vital bodily functions. The disease may result as a response to either of the ­following factors as discussed in Table 4.2.

• Environmental factors: Industrial hazards, natural calamities and malnutrition.
• Infective agents: Worms, protozoan, bacteria, fungi and virus.
• Inherent defect of the organism: Genetic anomalies.
• Combination of the factors mentioned above.

Classification of some common diseases in humans

These changes leads to various symptoms and signs of disease. Symptoms are the indication of the existence of something especially of an undesirable situation where we feel that something is going wrong in our body. Headache, cough, dysentery, vomiting are all symptoms of ill health.

These symptoms indicate the persistence of a disease, but they do not indicate what kind of disease it is. For example, a headache may occur due to examination stress or meningitis, or migraine, etc., or any one of the several different reasons.

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The signs and symptoms of a disease are used interchangeably in common practice. However, there is a fine difference between the two terms. When we develop cough or headache or diarrhoea or a wound with pus at some point of time in life. These are all symptoms indicating discomfort but it does not indicate a specific disease.

For example, the symptoms of Chikungunya include high fever, headache, pain behind the eyes, severe joint and muscle pain, nausea, vomiting and skin rashes which can be mistaken for flu or any other viral infections. On the basis of these symptoms, a physician may diagnose Chikungunya infection with a blood test to check for the virus causing the presence of a particular disease.

Sources of Disease

There are various factors which directly or indirectly impair human health. There are two different types of sources, such as intrinsic or internal factors and extrinsic or external factors.

Intrinsic or Internal Factors

The disease causing factors which are found inside our body are termed as intrinsic factors. The vital intrinsic factors responsible for humans to feel ill are as follows.

• Genetic disorders
• Impairment of immune system.
• Improper functioning of body organs, such as heart, liver, kidney, etc.
• Hormonal imbalances are discussed in Table 4.3 (hypo or hypersecretion causes various diseases, like dwarfism, gigantism and diabetes).

Common diseases due to hypersecretion or hyposecretion of hormones

Extrinsic or External Factors

These are the diseases causing external agents which enter our body from outside. The various external factors involved are as follows.

• Insufficient diet or unbalanced diet makes a person unhealthy and prone to nutritional deficiency and acquire other diseases.
• Various pathogenic agents, like bacteria, fungi, virus and worms, etc., are external agents.
• Environmental pollutants like oxides of carbon, sulphur and nitrogen, heavy metals like mercury, lead and arsenic, pesticides may also affect our health.
• Tobacco, alcohol and narcotic drugs may also contribute to body ailments.

Some common deficiency diseases in human beings

 

Chapter 4 Why Do We Fall Ill Types Of Diseases

Acute and Chronic Disease

Based on the duration for which a disease persists, it can classify human diseases into either acute or chronic. Any disease that causes malfunctioning of some parts of the body will impact our general health. Common cold and cough is commonly observed by us from time to time.

Most of us recover and get better very soon and there are no bad effects on general health. In case of acute diseases, we do not lose weight or become short of breath or tired. On the other hand, when we get infected with a chronic disease, such as tuberculosis of lungs and AIDS, it results in the loss of weight and tiredness of the individual.

• Acute disease: Disease such as common cold whose symptoms are rapidly ­visible is termed as acute disease.
• Chronic disease: Disease such as tuberculosis that are long-term and whose symptoms last for months or years are termed as chronic disease.

Difference between acute and chronic diseases

Congenital and Acquired Disease

Based on the occurrence of disease in the body since birth or after birth, the type of disease may be broadly classified as follows.

• Congenital disease: The disease which is present since birth as a result of genetic abnormalities or metabolic disorders is known as congenital disease.
• Acquired disease: The disease that develops after birth is known as acquired disease. They are further divided into two categories, such as (a) infectious or communicable disease; (b) non-infectious or noncommunicable disease.

Infectious diseases are caused by pathogens, such as viruses, bacteria, fungi and protozoans. Non-infectious diseases are caused due to inadequate diet, such as scurvy, kwashiorkor, etc.

Characteristics difference between congenital and acquired diseases

 

Chapter 4 Why Do We Fall Ill Infectious Diseases

Infectious Agents 

Infectious diseases are caused by pathogenic microorganisms, such as ­bacteria, viruses, parasites or fungi. The diseases can be spread, directly or indirectly from one person to another in a community.

The living world has enormous biodiversity classified into different groups and this classification is based on common characteristics among different organisms. Organisms that can cause diseases are found in a wide range of categories and it can be classified. Some of them are viruses, bacteria, fungi, protozoan’s (unicellular organisms) and worms (multicellular organisms).

Some of the common examples of diseases caused by viruses are common cold, influenza andAIDS. Diseases like typhoid, fever, cholera, tuberculosis and anthrax are caused by bacteria. Various common skin infections are caused by different kinds of fungi. Protozoan microbes cause diseases, such as malaria and kalaazar, sleeping sickness while elephantiasis is a worm infection.

• Viruses: Common cold, influenza, dengue fever, AIDS, chicken pox, measles and mumps.
• Fungi: Many common skin infections such as ringworm and athlete’s foot.
• Protozoans: Malaria, kala-azar, sleeping sickness.
• Bacteria: Typhoid fever, cholera and tuberculosis.
• Worms: Intestinal infections such as ascariasis, a parasitic infection by roundworm and elephantiasis, a parasitic infection caused by roundworm.

Why it is important to consider different kinds of infectious agents? 

It is important to consider different kinds of infectious agents because

The answerlies within the mode of treatment to be chosen forthe disease.All these infectious agents have many biological characteristics in common. All viruses live inside the host cells where they multiply and increase their progeny, whereas bacteria very rarely follow the same procedure. Viruses, bacteria and fungi have high multiplication capacity whereas worms as compared to the pathogens multiply very slowly.

Here, the term common traits refer to the similarity observed in the biochemical processes in the cell. As a result, the drugs that block one of these biochemical pathways in one member of the group is likely to be effective against many other members of the same group. But the same drug will remain ineffective against a pathogen belonging to a different group.

For instance, let us talk about the antibiotic penicillin, it blocks the synthesis of the cell wall in bacteria. Many bacteria makes a cell wall to protect themselves against the immunological response of the host. As a result, the growing bacteria lose its capacity to synthesize cell walls, and die easily. Human cells cannot synthesize cell wall at any point of time in their life.

Therefore, penicillin remains passive on us. On the other hand, viruses do not use these biochemical pathways and therefore, remains passive on humans. If we have viral infection (cold), then taking antibiotics does not mitigate the severity or the tenure of the disease. Instead, our body produces an antiviral protein called interferon to combat with viral infection, whereas if we get a bacterial infection along with viral cold, then taking antibiotics will complement its efficacy.

Common infectious diseases caused by various pathogens in humans

Means of Spread

How do infectious diseases spread? Most of the microbes are transmitted from an affected person to an immunized person in a variety of ways. They can be ‘communicated’ from one person to the other and so are also called communicable diseases. There are various modes of spreading the infection from an infected person to a healthy ­person through various modes which are broadly classified into two types and they are as follows.

• Indirect transmission: It occurs when there is no direct human to human contact. The spreading of diseases is through air, water, vectors and contaminated surfaces and objects.
• Direct transmission: It occurs when there is a physical contact between the infected and susceptible person. It includes sexual contact, animal bites and contact with soil. Let us discuss each of them in detail.

Indirect Transmission

• Airborne disease: Influenza, pneumonia and tuberculosis are the prominent examples of airborne ­diseases. The transmission occurs through little droplets thrown out by an infected person who sneezes or coughs towards someone standing in the vicinity of the infected person who inhales the droplets providing microbes a chance to infect the new host.
• Waterborne disease: Diseases can also spread through contaminated water. Cholera, typhoid are ­prominent instances of waterborne diseases. It occurs when the excreta of someone suffering from an infectious disease gets mixed with the drinking water used by people living nearby. The cholera causing microbes enter new hosts through the water they drink.

Direct Transmission 

• Sexually transmitted diseases (STD): Syphilis, gonorrhoea and AIDS are some examples of sexually transmitted diseases. The pathogens for these diseases are transmitted through sexual intercourse between the two partners. However, such sexually transmitted diseases are not spread by casual physical contact such as handshakes or hugs or sports, like wrestling, or by any of the other ways in which we touch each other socially.
• Animal bites: Certain diseases spread through the bite of infected animals. For example, rabies virus is transmitted to a healthy person through the bite of animals that has infected its saliva.
• Contact with soil: Many pathogens can enter the human body from soil through injuries. For example, the bacteria responsible for causing tetanus are usually found in soil and it enters the body through cuts or wounds caused by contaminated objects.
• Vector transmitted diseases: We live in an atmosphere endowed with a wide variety of animal species ahead of us. Most of the diseases are transmitted by other animals. These agents carry the infecting agents from a sick person to another potential healthy host (Table 4.8). These agents act as mediators in spreading infection and hence, they are called vectors. Vectors are also known as carrier of a disease. The most common vectors we all know are mosquitoes. In many species of mosquitoes, the female anopheles needs highly nutritious food in the form of blood to lay mature eggs. Mosquitoes feed on many warm blooded animals, including humans transmitting diseases from person to person.

Human diseases transmitted by various vectors

Chapter 4 Why Do We Fall Ill Symptoms of Disease: Organ Specific And Tissue Specific Manifestations

The microbes can enter into the body through various routes. The large size of human body offers all the possible places, organs or tissues, where they can reside and ­multiply. Different species of microbes can reside in different parts of the body. The most important thing that determines the destination of microbe is the point of entry.

• If they enter from air through the nose, they are likely to go to the lungs as in the case of mycobacterium tuberculosis, which causes tuberculosis.
• If they enter through the mouth, they can stay in the gut lining as in the case of typhoid causing bacteria, Salmonella typhi.
• HIV virus enters into the body through sexual contact and spreads to lymph nodes all over the body. Plasmodium enters through mosquito bite, it reaches to the liver and finally to the red blood cells.

Thus, symptoms of a disease completely depends on the targeted tissue or organ. If the lungs are the target, then symptoms will be cough and breathlessness. If the liver is targeted, then there would be jaundice. If the brain is the target, then headache, vomiting and unconsciousness are the signs.

In addition to these tissue-specific effects of infectious diseases, there may be other common effects which depend on the activation of the immune system. As the pathogen enters into the body of the host our immune system becomes activated and various immune cells like neutrophils, macrophages reach to the site of infection. The aggregation of these immune cells at the site of injury is called inflammation. In response to the invasion, our immune cells lead to the production of antibodies to eliminate that pathogen.

In some cases, the tissue-specificity of the infection leads to very general seeming effects. For example, in case of HIV, the virus on entering the body reaches the immune system to damage its functioning. Therefore, the body can no longer fight with even minor infections. As a result, even a small cold may lead to pneumonia.

Similarly, a minor gut infection can lead to diarrhoea with resulting in the loss of body fluids. Ultimately, other opportunistic infections kill people suffering from HIV-AIDS. It is also important to note that the severity of disease manifestations depend on the number of microbes entering into the body.

If the number of microbes is very small, the disease manifestations may be minor, whereas if the number of microbes is huge then the disease can be severe enough to be life-threatening. The immune system is a prominent factor that determines the number of microbes surviving in the body.

Principle of Treatment

What are the various preventative measures adopted by your family when you fall sick? When does the treatment involve medicines? Basically, there are two ways to treat an infectious disease. One would be to reduce the effect of the disease and the other to kill the causative agent. For the first, we can provide the treatment which will reduce the symptoms. For example, we can take medicines that bring down fever, reduce pain and assist in the recovery.

The treatment may reduce the severity of infection; but it is not enough to kill the pathogen. Hence, the disease may not cure and persist in our body depending upon the nature of pathogen. So, we need to remove the microbes from our body by neutralizing them. How do we kill microbes? One way is to use medicines that interfere with the synthesis of cell wall or various biochemical metabolic pathways to neutralize the pathogen as we discussed earlier.

For example, our cells make new substances by a mechanism which differs from that used by bacteria. We have to find a drug that blocks the synthesis of bacterial biochemical pathway without affecting our own. This can be achieved by the application of antibiotics. Similarly, there are drugs that kill protozoa such as the malarial parasite.

The reason why making anti-viral drugs are more difficult to is that viruses have few biochemical pathways of their own. They enter our cells and replicate its genome with the host’s genome and use our machinery for their life processes and survival.

Principle of Prevention of Disease

There are some limitations to treat an infectious disease and they are discussed below:

• Firstly, when someone is suffering from a disease his body becomes weak and takes time to recover completely.
• Secondly, the treatment takes time which means that someone suffering from a disease will definitely be confined to bed till convalescence.
• Thirdly, the individual suffering from an infectious disease may acts as a potent source to spread ­infection to other people or to the community.

Due to these limitations, it is popularly suggested that ‘Prevention of diseases is better than cure’.

There are various ways by which we can prevent the occurrence of disease and the following are as follows.

• For airborne infection, we can prevent exposure by providing living conditions that are not overcrowded.
• For waterborne infection, we can prevent exposure by procuring clean drinking water.
• For prevention from vector borne infections, clean environment is necessary.
• For example: Mosquito breeding can be stopped by ensuring cleanliness of water.
• Public hygiene and proper sanitation is the panacea to prevent infection

Chapter 4 Why Do We Fall Ill Vaccination

Vaccination is the administration of antigenic material to stimulate an individual’s immune system to generate adaptive immune response against the pathogen.

Nowadays, there is no reported case of smallpox anywhere across the globe, but consider a situation (hundred years ago) when smallpox epidemics was there. In such an epidemic, people feared of coming in contact with the sufferers to avoid the ­invasion of infection.

If a person encounters small pox once in his lifetime, the individual develops immunity against the disease for lifetime. This happens because when the immune system first recognizes an infectious particle, it responds against it and then remembers its specificity and develops the immunological memory for subsequent infections against the same pathogen.

So, when the same pathogen enters into the body of the host, now, this time the immune response is potent and intense to neutralize the antigen from the body. It is the basic principle of vaccination or immunization.

Chapter 4 Why Do We Fall Ill Various Diseases Caused By Pathogenic Agents

Diseases Caused by Viruses

Influenza

It is also known as Flu which is spread by influenza virus. In general, there are three strains of viruses A, B and C. Strains A and B are referred to as the common strains as they infect individuals throughout the world. Virus enters through our respiratory tract and affects the epithelial lining of mucous membrane of nose and throat. It spreads from person to person and also through airborne infection by coughing and sneezing as discussed earlier.

• Symptoms: The symptoms include sudden discharge from the nose, fever, headache, throat pain and later on as the ­infection progresses, body ache, muscular pain and inflammation takes place.
• Prevention: We should stay away from infected people. Use mask or ­handkerchief.
• Control: There is no effective measure against influenza. However, vaccines or antiviral drugs like Amantadine and Rimantadine are used.

Rabies (Hydrophobia)

Rabies spreads through the bite of mammals, like dogs, monkeys, cats, rabbits, etc. Rabies is a deadly disease and it is caused by the virus present in the saliva of infected animals. It enters into the blood and reaches to the brain and from brain, it is transmitted to different parts of the body.

• Symptoms: Severe headache, muscular pain, high fever, difficulty in swallowing, nausea followed by excessive salivation, difficulty in taking liquid foods and finally, fears of water develop. Hence, it is called hydrophobia.
• Prevention
• • Wash the wound immediately with water or with any antiseptic.
  • Mandatory immunization of stray dogs or other animals and also of pet dogs.
• Control: Rabies can be treated with Pasteur’s treatment discovered by Louis Pasteurin which 14 vaccines were given. Nowadays, only 5 anti-rabies vaccines are given at an interval of 0–3–7–14–30 days of dog bite.

Hepatitis or Jaundice

It is a liver disease and any kind of inflammation in liver due to jaundice leads to the impairment of digestion. The types of hepatitis are Hepatitis A, Hepatitis B, Hepatitis C, Hepatitis D and Hepatitis E. It usually spreads through contaminated food or water contaminated with hepatitis virus.

Hepatitis A: Hepatitis is an acute infectious disease of liver that affects both children and adult.

• Symptoms: High body temperature, headache, fatigue, joint paints, vomiting, nausea, loss of appetite, dark yellow skin and urine due to the presence of pigment named bilirubin and light coloured stool within 3–10 days of infection.
• Prevention
• • Use of chlorinated, boiled or mineral water.
  • Hands should be washed after cleaning the bed and vessels of the patients.
  • Proper vaccination.
• Control
  • Application of interferon injection as administered by the doctor.
  • Patient should be fed with high calorie liquid diet like juices, radish, etc.
  • Protein and fat rich diet should be avoided.

Hepatitis B: Hepatitis B is commonly known as ‘serum or transfusion’ hepatitis. This is the most fatal and common type of viral hepatitis among communities. The infection spreads through the infected blood from mothers to their babies or by sexual routes.

• Symptoms: Acute liver disease turned to chronic one, hepatic carcinoma, liver cirrhosis, etc.
• Prevention
• • Alcoholics or liquor should be avoided.
  • Intercourse with more than one partner (promiscuous) should be avoided.

Poliomyelitis

Polio is caused by Polio virus. The virus enters into our body through food and water and reaches the intestine. From bloodstream, it reaches to the CNS (Brain and spinal cord) where it destroys the motor nerves leading to paralysis of body parts, mainly legs.

Children between the age group of 6 months to 5 years are more prone to infection. It is transmitted among children by fecal-oral route through food or water contaminated with stools of patients.

• Symptoms: The symptoms include sore throat and headache. As the infection ­progresses, fever, muscular pain, vomiting, stiffness of the neck and legs enhances and ultimately, paralysis of legs occurs.
• Prevention
• • Physiotherapy helps in the early phase of viral attack to reduce the paralytic effect.
  • Proper disposal of wastes.
  • Proper hygiene and sanitation should be maintained.

AIDS

The term AIDS implies acquired immune deficiency syndrome. It is a fatal disease caused by human immunodeficiency virus (HIV), a retrovirus or RNA virus. When HIV virus enters the body, it attacks the major immune cells of our body like T-helper cells and macrophages. Later, the person becomes immune-deficient, who is prone to other opportunistic infections (secondary infections). The person dies of secondary infections.

• Transmission: Transmission of HIV virus takes place through the following ways.
• • HIV virus spreads through unprotected intercourse.
  • AIDS spreads through contaminated blood having HIV virus during blood transfusion.
  • During vertical transmission, the mother infected with AIDS may transmit the virus to her offspring during pregnancy.
  • It can also be spread through the use of contaminated injections, needles, syringes, etc.
• Symptoms: Symptoms include regular fever, weight loss, shivering, swelling of lymph nodes, sweating at night, and in the later stage of the disease, amnesia and aphasia are observed.
• Prevention and control
  • There is no effective medicine or vaccine that has been developed for its prevention.
  • People should be made aware of AIDS by starting a general awareness programme.
  • Syringes or needles once used should not be used again.
  • Sexual contact with the HIV infected person should be avoided or condoms should be used.
  • Contaminated blood should never be transfused and before transfusion , blood screening for HIV infection should be mandatory.
  • Common razors and blades should not be used.

Some communicable diseases

Chapter 4 Why Do We Fall Ill Diseases Caused By Bacteria

Tuberculosis

Tuberculosis, a communicable disease was first discovered by the German scientist, Robert Koch in the year 1882. He was awarded Nobel Prize for the discovery in 1905. It is caused by Mycobacterium tuberculosis. Mycobacterium enters through respiratory tract and reaches through various parts of the body, such as lungs, intestine and lymph glands.

After entering the body, the bacteria releases a toxin called tuberculin. The chances of infection are increased when a person inhales the infected droplets through coughing, sneezing, spitting of the infected person.

• Symptoms: The incubation period of tuberculosis includes from few weeks to a few years. The patient infected with tuberculosis feels sick and weak with a gradual loss of appetite and weight. The symptoms of tuberculosis depends upon the pathogen entering into the body and the organ it is infecting.
• Prevention
• • Proper hygiene and sanitation.
  • Infected person should be isolated and proper rehabilitation is necessary.
  • Immunization with Bacillus-Calmette-Guerin (BCG) prevents tuberculosis.
• Control: Tuberculosis can be cured by various drugs but the major ones are ­Rifampicin, Streptomycin, Thioacetozone, etc.

Cholera

It is an acute infectious disease caused by Vibrio cholerae and it is transmitted through flies, contaminated water and food. The bacterium enters through the digestive tract and it reaches the intestinal epithelial cells and multiplies there.

It releases AB toxin which causes irritation in the epithelial lining of the cells leading to the secretion of large amount of water and salts out of the body. The incubation time of bacteria is few hours to days.

• Symptoms: Major diagnostic symptoms include watery stool, vomiting, dehydration with heavy loss of water and body fluids with electrolytes, loss of body weight, weakness, shrinking of eyes, etc.
• Prevention
• • Person should be immunized with cholera vaccine.
  • Boiled water and cooked food should be taken by patient.
  • Proper hygiene and sanitation.
• Control
  • To prevent dehydration, oral rehydration solution (ORS) should be taken immediately and intermittently.
  • ORS includes electrolytes like sodium, potassium, chloride, etc. A drug named tetracycline is proved to be effective against the bacterium.

Typhoid

It is caused by Salmonella typhi found in the intestine of humans. It is the widest and most common communicable disease among communities. Salmonella is a rod-shaped motile bacterium, it enters through the oral route by contaminated food or water with faecal matter of typhoid patients. The onset of the infection begins through faecal matter. The symptoms appear within 10–14 days after infection.

• Symptoms
• • Symptoms of the typhoid fever include continuous fever, headache with ­delirium (disorder of the mind), slow pulse, distended abdomen, watery stool and appearance of rashes on the body.
  • Headache and fever reaches to its peak in the afternoon. The temperature rises each day in the first week and declines during the third or fourth day.
• Prevention
  • Proper hygiene and sanitation.
  • Disposal of faecal matter should not be avoided.
  • TAB vaccination should be given as it provides immunity up to 3 years.
• Control: Chloromycetin, an important drug, is used to treat typhoid fever.

Diarrhoea

The main cause of diarrhoea is food poisoning. In case of food poisoning, the bacteria grows in food and releases toxin. When the food is ingested, toxins are released into the blood and absorbed by the gastrointestinal tract. In this case, the person frequently discharges semi-solid or watery stool.

The infection occurs through contaminated food, water, clothes and bed sheets, etc. There are various causative agents of diarrhoea like the bacteria E. coli, Salmonella, protozoan’s like Entamoeba histolytica, Giardia intestinalis and Balantidium, viruses like Rotavirus, Enterovirus, Adenoviruses and nematode or roundworm Ascaris.

• Symptoms
• • The major symptoms include dehydration, loss of appetite, nausea, vomiting, abdominal cramps, fever, hypotension, mucus and blood in the stool. It is one of the major causes of infant mortality in India.
  • Due to dehydration, major loss of water, electrolytes and body fluids take place leading to the death of the person.
• Prevention
  • Proper hygiene and sanitation.
  • Before taking eatables, hands should be washed properly.
  • Before taking any consumable, they should be washed properly.
• Control
  • To prevent dehydration, oral rehydration solution (ORS) should be taken immediately and intermittently.
  • Liquid stuff such as pulse soup, rice water, porridge (Khichdi), isabgol with water or curd should be given.
  • Microbial drugs.
  • Complete bed rest until patient recovers completely.

Anthrax

The causative agent of anthrax is a rod shaped non-motile bacteria, Bacillus anthracis. This disease is more common in wild and domestic animals, like sheep, horse, pig, ­cattle and including humans. The disease is transmitted by eating uncooked meat of infected animals.

• Symptoms: Symptoms include vomiting, nausea, and loss of appetite, pain and as the disease advances it leads to the death of person.
• Prevention: Vaccination is the only way to cure this disease.
• Control: Antibiotics should be taken to control it.

Peptic Ulcers

These are the inflammatory painful bleeding regions in the stomach and ­duodenum due to frequent consumption of fast or junk food. However, occurrence of peptic ulcer is also possible in certain lifestyle. Stressful life also increases the gastric acidic secretion and leads to the development of peptic ulcers.

Two Australians made a breakthrough that a bacterium called Helicobacter pylori was the causative agent for peptic ulcers. Robin Warren (born 1937), a pathologist from Perth, Australia, saw these small curved bacteria in the lower part of the stomach in many patients. He noticed the symptoms of inflammation around these bacteria.

Barry Marshall (born 1951), a young clinical fellow became interested in Warren’s findings and succeeded in isolating the bacteria from these sources. Marshall and Warren found that an antibiotic Amoxicillin is the cure for this disease and later on due to his findings both were awarded Nobel prize for 2005 in Physiology and Medicine.

• Prevention
• • Fast or junk food should be avoided.
  • Spicy and oiled food stuff should be avoided.
• Control
  • If acidity persists for a long time, then immediately consult the doctor.
  • Amoxicillin drug is advised.

Chapter 4 Why Do We Fall Ill Diseases Caused By Protozoa

Malaria

According to reports, more than two millions of people die every year due to malaria. It is caused by Plasmodium and it spreads through the bite of vector, female Anopheles mosquito.

• Symptoms: Symptoms include extreme cold, shivering, nausea, vomiting, headache, high fever, tachycardia, high respiration, muscular pain, and at the end extreme sweating occurs and body temperature comes to normal. In few cases, enlargement of spleen and liver is reported.
• Prevention
• • Mosquito nets should be used while sleeping.
  • Wire gauze should be used on windows and doors to prevent the entry of mosquitoes.
  • Insect repellents should be used.
• Control
  • Quinine, a drug extracted from the bark of the cinchona tree is used to deal with malarial parasite.
  • Mosquito larvae should be destroyed by adding fumigants or kerosene oil.
  • Biological control is an effective measure to control the population of larvae. The introduction of Gambusia fish in the water body naturally kills the larvae.
  • By undergoing chemical control with the application of insecticides like DDT, Malathion and Parathione, malaria can be effectively prevented.
  • The breeding grounds, pits, ditches around human dwellings should be drained and the collection of water in cooler, water tanks, tyres, etc., should be avoided.

Chapter 4 Why Do We Fall Ill Classroom Corner Fill In The Blanks

Question 1. The pathogens of disease are ______.
Answer. Protozoa

Question 2. ______ are the organisms which carry specific germs.
Answer. Vectors

Question 3. Plague is transmitted by ______.
Answer. Rat Fleas

Question 4. ______ is the diseases for which the first vaccine was developed from living organisms.
Answer. Small Pox

Question 5. ______ are the inactive toxic substances extracted from bacteria.
Answer. Toxoids

Question 6. Small pox vaccine contains ______ virus.
Answer. Cowpox

Question 7. ______ is the pathogen which is responsible for ascariasis.
Answer. Ascaris Lumbricoides

Question 8. Anopheles spreads by ______.
Answer. Malaria

Question 9. ______ is the vaccine used to cure the disease caused by Salmonella typhi.
Answer. Typhoid

Question 10. Trachoma is an infection in the ______.
Answer. Eye

Question 11. ______ is a fatal disease that reduces the immunity of the body.
Answer. Aids

Question 12. Disease which is transmitted through placenta is ______.
Answer. German Measles

Question 13. The immunity developed in our body due to the vaccination of polio and measles is an example of ______.
Answer. Artificial Active Immunity

Question 14. ______ diseases occur occasionally or irregularly.
Answer. Acute

Question 15. Pathogens contain unique type of protein called ______ which causes diseases in our body.
Answer. Antigen

Chapter 4 Why Do We Fall Ill Match The Columns

Question 1.

Select the correct option.

1. A-1, B-2, C-3, D-4
2. A-4, B-2, C-1, D-3
3. A-4, B-1, C-2, D-3
4. A-1, B-3, C-2, D-4

Answer. 3. A-4, B-1, C-2, D-3

Question 2.

Select the correct option.

1. A-1, B-2, C-3, D-4
2. A-4, B-3, C-1, D-2
3. A-4, B-1, C-2, D-3
4. A-1, B-3, C-2, D-4

Answer. 2. A-4, B-3, C-1, D-2

Question 3.

Select the correct option.

1. A-1, B-2, C-3, D-4
2. A-4, B-3, C-1, D-2
3. A-4, B-1, C-2, D-3
4. A-3, B-4, C-2, D-1

Answer. 4. A-3, B-4, C-2, D-1

Question 4.

Select the correct option:

1. A-4, B-1, C-3, D-2
2. A-4, B-3, C-1, D-2
3. A-4, B-1, C-2, D-3
4. A-3, B-4, C-2, D-1

Answer. 1. A-4, B-1, C-3, D-2

Question 5.

Select the correct option:

1. A-4, B-1, C-3, D-2
2. A-4, B-3, C-1, D-2
3. A-4, B-1, C-2, D-3
4. A-3, B-4, C-2, D-1

Answer. 4. A-3, B-4, C-2, D-1

Chapter 4 Why Do We Fall Ill Multiple Choice Question And Answers

Direction: Choose the correct option for each question. There is only one correct response for each question.

Question 1. Cells are the basic units of

1. human beings
2. living beings’
3. proteins
4. well-being

Answer. 2. living beings

Question 2. Cells are made of a variety of which of the following chemical substances?

1. Proteins
2. Carbohydrates
3. Fats or lipids
4. All the above

Answer. 4. All the above

Question 3. The heart is beating, the lungs are ­breathing, the kidney is filtering urine, the brain is

1. responding
2. reacting
3. thinking
4. elaborating

Answer. 3. thinking

Question 4. If the kidneys are not filtering urine, poisonous substances will

1. accumulate
2. disperse
3. dissipate
4. scatter

Answer. 1. accumulate

Question 5. Which of the following is a necessity for cell and tissue functions?

1. Proteins
2. Carbohydrates
3. Fats or lipids
4. Food

Answer. 4. Food

Read and Learn More NEET Foundation Multiple Choice Questions

Question 6. Good economic conditions and jobs are needed for an individual to maintain

1. health
2. wealth
3. standard of living
4. reputation

Answer. 1. health

Question 7. A state of physical, mental and social well-being is called

1. wealth
2. standard of living
3. reputation
4. health

Answer. 4. health

Question 8. Which of the following helps to digest the food taken in?

1. Digestive system
2. Intestine
3. Stomach
4. Kidney

Answer. 1. Digestive system

Question 9. Which of the following is made up of bones and muscles?

1. Musculoskeletal system
2. Digestive system
3. Intestine
4. Stomach

Answer. 1. Musculoskeletal system

Question 10. Which of the following holds the body parts together and helps the body move?

1. Digestive system
2. Intestine
3. Musculoskeletal system
4. Stomach

Answer. 3. Musculoskeletal system

Question 11. Signs of disease are what physicians will look for on the basis of

1. symptoms
2. causes
3. digestive system
4. outside the body

Answer. 1. symptoms

Question 12. Some diseases last for only very short period of time and these are called

1. chronic diseases
2. acute diseases
3. elephantiasis
4. infectious diseases

Answer. 2. acute diseases

Question 13. Other ailments can last for a long time, even as much as a lifetime and they are called

1. chronic diseases
2. acute diseases
3. elephantiasis
4. infectious diseases

Answer. 1. chronic diseases

Question 14. An example is the infection causing elephantiasis, which is very common in some parts of

1. West Indies
2. Sri Lanka
3. India
4. Africa

Answer. 3. India

Question 15. Diseases where microbes are the immediate causes are called

1. chronic diseases
2. acute diseases
3. elephantiasis
4. infectious diseases

Answer. 4. infectious diseases

Question 16. Some cancers are caused by which of the following?

1. Liver abnormalities
2. Lungs abnormalities
3. Heart abnormalities
4. Genetic abnormalities

Answer. 1. Liver abnormalities

Question 17. High blood pressure can be caused by excessive weight and

1. lack of exercise
2. genetic abnormalities
3. excessive salt
4. excessive sodium

Answer. 1. lack of exercise

Question 18. Chronic diseases therefore, have very drastic long-term effects on people’s health as compared to

1. chronic diseases
2. acute diseases
3. elephantiasis
4. infectious diseases

Answer. 2. acute diseases

Question 19. Marshall and Warren received the Nobel prize for physiology and medicine in

1. 2001
2. 2005
3. 2004
4. 2003

Answer. 2. 2005

Question 20. Some common examples of diseases caused by viruses are common cold, influenza, dengue fever and

1. AIDS
2. typhoid
3. tuberculosis
4. anthrax

Answer. 1. AIDS

Question 21. Diseases like typhoid fever, cholera, tuberculosis and anthrax are caused by

1. Worm
2. fungi
3. bacteria
4. virus

Answer. 3. bacteria

Question 22. Many common skin infections are caused by different kinds of

1. bacteria
2. virus
3. worms
4. fungi

Answer. 4. fungi

Question 23. Protozoan microbes cause many familiar diseases, such as malaria and

1. kala-azar
2. penicillin
3. typhoid
4. malaria

Answer. 1. kala-azar

Question 24. Each and everyone of us have also come across intestinal worm infections, as well as diseases like elephantiasis caused by different species of

1. bacteria
2. virus
3. worms
4. fungi

Answer. 3. worms

Question 25. The antibiotic penicillin blocks the bacterial processes that build

1. cell wall
2. vectors
3. lymph nodes
4. cowpox

Answer. 1. cell wall

Question 26. Many microbial agents that can commonly move from an affected person to someone else in a variety of ways are also called

1. commuting diseases
2. incommunicable diseases
3. communicable diseases
4. communic diseases

Answer. 3. communicable diseases

Question 27. It includes handshakes or hugs or sports, like wrestling, or by any of the other ways in which we touch each other socially, it is called

1. casual physical contact
2. formal physical contact
3. forced physical contact
4. potential physical contact

Answer. 1. casual physical contact

Question 28. Other than sexual contact, the AIDS virus can also spread through blood-to-blood contact with infected people orfrom an infected mother to her baby during pregnancy or through

1. hugs
2. saliva
3. touches
4. breast feeding

Answer. 4. breast feeding

Class 11 Physics	Class 12 Maths	Class 11 Chemistry
NEET Foundation	Class 12 Physics	NEET Physics

Question 29. These animals carry the infecting agents from a sick person to another potential host. These animals are thus the intermediaries and they are called

1. vectors
2. nectors
3. cell wall
4. lymph

Answer. 1. vectors

Question 30. Which of the following infection comes into the body through sexual organs and spreads to lymph nodes all over the body?

1. AIDS
2. Typhoid
3. Tuberculosis
4. Anthrax

Answer. 1. AIDS

Question 31. Health is a state of

(1) physical

(2) mental

(3) social well-being

(4) economic

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1), (2) and (4)

Answer. 1. (1), (2) and (3)

Question 32. Diseases are classified depending on their duration.

(1) Acute

(2) Chronic

(3) Mental

(4) Physical

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 4. (1), (2), (3) and (4)

Question 33. Disease may be due to causes like

(1) microscopic

(2) non-infectious

(3) multicellular

(4) infectious

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (2) and (4)
4. (1), (3) and (4)

Answer. 3. (2) and (4)

Question 34. Infectious agents belong to different ­categories of organisms and may be

(1) unicellular

(2) single cellular

(3) microscopic

(4) multicellular

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 3. (1), (3) and (4)

Question 35. Infectious agents are spread through

(1) air

(2) water

(3) physical contact

(4) vectors

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 2. (1), (2), (3) and (4)

Question 36. Effective prevention of infectious diseases in the community requires that everyone should have access to

(1) air

(2) water

(3) public hygiene

(4) immunization

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (3) and (4)

Answer. 4. (3) and (4)

Question 37. Cells are made of a variety of chemical substances, such as

(1) proteins

(2) carbohydrates

(3) fats

(4) lipids

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (3) and (4)

Answer. 2. (1), (2), (3) and (4)

Question 38. In our organs or tissues, various specialized activities are carried out, such as

(1) heart is beating.

(2) lungs are breathing.

(3) kidney is filtering urine.

(4) brain is thinking.

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (3) and (4)

Answer. 2. (1), (2), (3) and (4)

Question 39. Health means a state of

(1) physical

(2) mental

(3) social well-being

(4) living standard

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (3) and (4)

Answer. 1. (1), (2) and (3)

Question 40. The digestive system helps to digest food taken in from outside the body.

(1) Stomach

(2) Intestines

(3) Kidney

(4) Liver

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 4. (1) and (2)

Question 41. The musculoskeletal system holds the body parts together and it helps the body move, it is made up of

(1) liver

(2) bones

(3) muscles

(4) immune system

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (2) and (3)

Answer. 4. (2) and (3)

Question 42. High blood pressure can be caused by

(1) excessive weight

(2) lack of exercise

(3) musculoskeletal

(4) inflammation

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 4. (1) and (2)

Question 43. Diseases are found in a wide range of such categories of classification, such as

(1) viruses

(2) bacteria

(3) fungi

(4) worms

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 2. (1), (2), (3) and (4)

Question 44. The common examples of diseases caused by viruses are

(1) common cold

(2) influenza

(3) dengue fever

(4) AIDS

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 2. (1), (2), (3) and (4)

Question 45. The diseases caused by bacteria are

(1) typhoid fever

(2) cholera

(3) tuberculosis

(4) anthrax

1. (1), (2) and (3)
2. (1), (2), (3) and (4)
3. (1), (3) and (4)
4. (1) and (2)

Answer. 2. (1), (2), (3) and (4)

Question 46. Which is a chronic disease?

1. Tuberculosis
2. Night blindness
3. Cholera
4. Rickets

Answer. 3. Cholera

Question 47. Which one is not a sexually transmitted disease?

1. AIDS
2. Gonorrhoea
3. Syphilis
4. Diabetes

Answer. 4. Diabetes

Question 48. Which one is not a bacterial disease?

1. TB
2. Typhoid
3. Pneumonia
4. Poliomyelitis

Answer. 4. Poliomyelitis

Question 49. AIDS can be transmitted through

1. Blood transfusion
2. Pregnant mother to foetus
3. Sexual contact
4. All the above

Answer. 4. All the above

Question 50. Which one of the following is a deficiency disease?

1. Diabetes
2. Malaria
3. Goitre
4. Tetanus

Answer. 3. Goitre

Question 51. Which is not an infectious disease?

1. Diabetes
2. TB
3. Leprosy
4. Typhoid

Answer. 1. Diabetes

Question 52. Which disease is caused due to deficiency of a hormone?

1. Chickenpox
2. Diabetes
3. AIDS
4. Malaria

Answer. 2. Diabetes

Question 53. Common cold is a/an

1. genetic disorder
2. acute disease
3. chronic disease
4. deficiency disease

Answer. 2. acute disease

Question 54. Choose the wrong statement.

1. High blood pressure is caused by excessive weight and lack of exercise
2. Cancers can be caused by genetic abnormalities
3. Peptic ulcers are caused by eating acidic food
4. Acne is not caused by staphylococcl

Answer. 4. Acne is not caused by staphylococcl

Question 55. We should not allow mosquitoes to breed in our surroundings because they

1. multiply very fast and cause pollution
2. are vectors for many disease
3. bite and cause skin disease
4. are not important insects

Answer. 2. are vectors for many disease

Question 56. Which one of the following causes kala-azar?

1. Ascaris
2. Trypanosoma
3. Leishmania
4. Bacteria

Answer. 3. Leishmania

Question 57. Which disease is not transmitted by mosquitoes?

1. Dengue
2. Malaria
3. Brain fever or encephalitis
4. Pneumonia

Answer. 4. Pneumonia

Question 58. Which one of the following is not important for individual health?

1. Living in clean space
2. Good economic condition
3. Social equality and harmony
4. Living in a large and well furnished house

Answer. 4. Living in a large and well furnished house

Question 59. Which one of the following is not a viral disease?

1. Dengue
2. AIDS
3. Typhoid
4. Influenza

Answer. 3. Typhoid

Question 60. Which one of the following is not a ­bacterial disease?

1. Cholera
2. Tuberculosis
3. Anthrax
4. Influenza

Answer. 4. Influenza

Question 61. The technique of providing immunity by vaccination was first developed by

1. Robert koch
2. Alexender fleming
3. William harvey
4. Edward Jenner

Answer. 4. Edward Jenner

Question 62. ‘Penicillin’ a life saving antibiotic, was discovered by

1. Alexander Fleming
2. Edward Jenner
3. H.G. Khorana
4. William Harvey

Answer. 1. Alexander Fleming

Question 63. For which disease ‘oral’ vaccine is given?

1. TB
2. Typhoid
3. Pertusis
4. Poliomyelitis

Answer. 2. Typhoid

Question 64. ‘BCG’ vaccine is given to infants for ­protection against

1. Diarrhoea
2. Cholera
3. Pneumonia
4. Tuberculosis

Answer. 4. Tuberculosis

Question 65. You are aware of Polio Eradication Programme in your city. Children are ­vaccinated because

1. vaccination kills the polio causing microorganisms
2. prevents the entry of polio causing organism
3. It creats immunity in the body
4. All the above

Answer. 3. It creats immunity in the body

Question 66. The chemicals that kill or stop the growth of certain kinds of microbes are called

1. vaccines
2. microbes
3. antibiotics
4. fungi

Answer. 3. antibiotics

Question 67. Penicillium is a/an

1. antibiotic
2. vaccine
3. alga
4. fungus

Answer. 4. fungus

Question 68. The diseases that can be transmitted through body fluids are

1. AIDS and hepatitis B
2. TB and typhoid
3. influenza and cholera
4. cholera and rabies

Answer. 1. AIDS and hepatitis B

Question 69. ‘Congential diseases’ are those which:

1. are these since birth
2. are inherited
3. are transmitted easily
4. are fatal

Answer. 2. are inherited

Question 70. Widal test helps to diagnose

1. Tetanus
2. Tuberculosis
3. Typhoid
4. Whooping cough

Answer. 3. Typhoid

Question 71. DPT Vaccine is for

1. Diptheria, Polio, Tetanus
2. Diptheria, Pertussis, Tetanus
3. Diptheria, Pertussis, Typhoid
4. Diptheria, Pertussis, Tuberculosis

Answer. 2. Diptheria, Pertussis, Tetanus

Question 72. World TB day is celebrated on

1. March 21
2. March 24
3. March 30
4. March 18

Answer. 2. March 24

Question 73. Polio is caused due to

1. bacteria
2. virus
3. fungi
4. helminthes worm

Answer. 2. virus

Question 74. The Pulse Polio Programme is organized in our country for

1. eradicating polio
2. spreading polio
3. curing polio
4. none of these

Answer. 1. eradicating polio

Question 75. AIDS day is celebrated on

1. 5th June
2. 1st October
3. 11th July
4. 1st December

Answer. 4. 1st December

Question 76. ______ depicts the notion of being well.

1. Health
2. Disease-free
3. Infectious body
4. Healthy agent

Answer. 1. Health

Question 77. ______ refers to the state of absence of comfort to perform daily activities. It depends on the individual only.

1. Disease-free person
2. Health-free body
3. Non-healthy body
4. Healthy body

Answer. 1. Disease-free person

Question 78. ______ is defined as an abnormal condition that disturbs or modifies the performance of vital functions of the body.

1. Disease
2. Health
3. Infection
4. Infectious agent

Answer. 1. Disease

Question 79. The vital intrinsic factors responsible for ill health of humans are ______.

1. genetic disorders
2. environmental hazards
3. pathogenic agents
4. protein malfunctioning

Answer. 1. genetic disorders

Question 80. ______ are the disease causing external agents, which enter our body from outside environment.

1. Extrinsic factors
2. Internal factors
3. External factors
4. Genetic factors

Answer. 1. Extrinsic factors

Question 81. Which disease is caused by virus?

1. AIDS
2. TB
3. Scabies
4. Dengue fever

Answer. 1. AIDS

Question 82. Whooping cough is caused due to which of the following disease?

1. Bacillus anthracis
2. Bordetella pertussis
3. Salmonella typhi
4. Clostridium tetani

Answer. 2. Bordetella pertussis

Question 83. Plasmodium causes which of the following disease?

1. Kala-azar
2. Dengue fever
3. Sleeping sickness
4. Pyorrhea

Answer. 2. Dengue fever

Question 84. Which of the following is an airborne disease?

1. Influenza
2. Typhoid
3. AIDS
4. Gonorrhoea

Answer. 1. Influenza

Question 85. Which of the following disease is transmitted due to louse?

1. Malaria
2. Filariasis
3. Epidemic typhus
4. Typhoid

Answer. 3. Epidemic typhus

Question 86. ______ are the examples of sexually-transmitted diseases.

1. AIDS
2. Cholera
3. Typhoid
4. Malaria

Answer. 1. AIDS

Question 87. ______ are the prominent examples of airborne diseases.

1. Tuberculosis
2. Malaria
3. Gonorrhoea
4. Syphilis

Answer. 1. Tuberculosis

Question 88. Elephantiasis is a ______.

1. worm infection
2. protozoan disease
3. airborne disease
4. waterborne disease

Answer. 1. worm infection

Question 89. Anthrax is caused by ______.

1. bacteria
2. virus
3. fungi
4. protozoan

Answer. 1. bacteria

Question 90. Which of the following is the causative agent of typhoid?

1. Treponema pallidum
2. Salmonella typhi
3. Vibrio cholerae
4. Bacillus anthracis

Answer. 2. Salmonella typhi

Question 91. Which of the following is the first cell to reach the site of infection?

1. Microphages
2. Neutrophil
3. RBC
4. Neuron

Answer. 2. Neutrophil

Question 92. If a person encounters ______ once in life, he develops immunity against it for life time.
Answer. Small pox

Question 93. In which disease the virus enters the respiratory tract and affects epithelial lining of mucus membrane?

1. Influenza
2. Rabies
3. Jaundice
4. Hepatitis

Answer. 1. Influenza

Question 94. Headache, nausea followed by hydrophobia develops in ______.
Answer. Rabies

Question 95. In ______ disease, the virus enters the CNS and destroys motor nerve leading to paralysis mainly in legs.
Answer. Polio

Question 96. Which of the following disease affects our lungs?

1. AIDS
2. Rabies
3. Polio
4. Tuberculosis

Answer. 4. Tuberculosis

Question 97. The BCG vaccine is given for the immunity against which disease?

1. Hepatitis
2. Jaundice
3. Tuberculosis
4. Malaria

Answer. 3. Tuberculosis

Question 98. Malaria is caused due to which of the following?

1. Protozoa
2. Anopheles mosquito
3. Both a and b
4. None of these

Answer. 4. None of these

Question 99. Plasmodium is an example of which of the following?

1. Virus
2. Bacteria
3. Protozoa
4. Worm

Answer. 3. Protozoa

Question 100. Diarrhea, cholera, typhoid are the diseases that have one thing in common that is

1. all of them are caused by bacteria.
2. all of them is transmitted by contaminated food and water.
3. all of them are cured by antibiotics.
4. all the above

Answer. 4. all the above

Question 101. HIV virus attacks which one of the following cells in our body?

1. Red blood cells
2. White blood cells
3. Liver cell
4. Long cell

Answer. 4. Long cell

Question 102. Penicillin is a drug that involves which of the following?

1. Interfere in the biological pathway of bacteria.
2. An antibiotic that can kill bacteria.
3. Both (a) and (b)
4. None of the above

Answer. 4. None of the above

Question 103. Which of the following disease is caused due to worm?

1. Tetanus
2. Rabies
3. Sleeping sickness
4. Filariasis

Answer. 4. Filariasis

Question 104. Which of the following is a bacteria?

1. Plasmodium
2. Trypanosome
3. Rabies virus
4. Salmonella typhi

Answer. 2. Trypanosome

Question 105. Which one of the following is not a viral disease?

1. Dengue
2. AIDS
3. Typhoid
4. Influenza

Answer. 3. Typhoid

Question 106. Which one of the following is not a bacterial disease?

1. Cholera
2. Tuberculosis
3. Anthrax
4. Influenza

Answer. 4. Influenza

Question 107. Which one of the following disease is not transmitted by mosquito?

1. Brain fever
2. Malaria
3. Typhoid
4. Dengue

Answer. 3. Typhoid

Question 108. Which one of the following disease is caused by bacteria?

1. Typhoid
2. Anthrax
3. Tuberculosis
4. Malaria

Answer. 4. Malaria

Question 109. Which one of the following diseases is caused by protozoans?

1. Malaria
2. Influenza
3. AIDS
4. Cholera

Answer. 1. Malaria

Question 110. Which one of the following has a long term effect on the health of an individual?

1. Common cold
2. Chicken pox
3. Chewing tobacco
4. Stress

Answer. 3. Chewing tobacco

Question 111. Which of the following can make you ill if you come in contact with an infected person?

1. High blood pressure
2. Genetic abnormalities
3. Sneezing
4. Blood cancer

Answer. 3. Sneezing

Question 112. AIDS cannot be transmitted by

1. sexual contact
2. hugs
3. breast feeding
4. blood transfusion

Answer. 2. hugs

Question 113. Making anti-viral drugs is more difficult than making anti-bacterial medicines because

1. viruses make use of host machinery.
2. viruses are on the border line of living and non-living.
3. viruses have very few biochemical mechanisms of their own.
4. viruses have a protein coat.

Answer. 3. viruses have very few biochemical mechanisms of their own.

Question 114. Which one of the following causes kala-azar?

1. Ascaris
2. Trypanosoma
3. Leishmania
4. Bacteria

Answer. 3. Leishmania

Question 115. If you live in a overcrowded and poorly ventilated house, it is possible that you may suffer from which of the following diseases?

1. Cancer
2. AIDS
3. Airborne diseases
4. Cholera

Answer. 3. Airborne diseases

Question 116. Which of the following disease is not transmitted by mosquitoes?

1. Dengue
2. Malaria
3. Brain fever or encephalitis
4. Pneumonia

Answer. 4. Pneumonia

Question 117. Which one of the following is not important for an individual’s health?

1. Living in clean space.
2. Good economic condition.
3. Social equality and harmony.
4. Living in a large and well-furnished house.

Answer. 4. Living in a large and well-furnished house.

Question 118. Choose the incorrect statement from the following.

1. High blood pressure is caused by excessive weight and lack of exercise.
2. Cancers can be caused by genetic abnormalities.
3. Peptic ulcers are caused by eating acidic food.
4. Acne in not caused by staphylococci.

Answer. 3. Peptic ulcers are caused by eating acidic food.

Question 119. We should not allow mosquitoes to breed in our surroundings because they

1. multiply very fast and cause pollution.
2. are vectors for many diseases.
3. bite and cause skin diseases.
4. are not important insects.

Answer. 2. are vectors for many diseases.

Question 119. You are aware of the ‘Polio Eradication Programme’ in your city. Children are vaccinated because

1. vaccination kills the polio causing microorganisms.
2. prevents the entry of polio causing organism.
3. it creates immunity in the body.
4. all the above

Answer. 3. it creates immunity in the body.

Question 120. Viruses, which cause hepatitis, are transmitted through

1. air
2. water
3. food
4. personal contact

Answer. 2. water

Question 121. Vectors can be defined as

1. animals carry the infecting agents from sick person to another healthy person.
2. microorganisms which cause many diseases.
3. infected person.
4. diseased plants.

Answer. 1. animals carry the infecting agents from sick person to another healthy person.

Question 122. State any two conditions essential for health.
Answer: The two conditions essential for good health are as follows.

• State of physical, mental and social well-being.
• Better surroundings or environment.

Question 123. State any two conditions essential for being free of disease.
Answer: The two conditions essential for being free of disease are as follows.

• Personal and domestic hygiene.
• Clean environment and surroundings.

Question 124. Define the term ’health’. Discuss the conditions essential to maintain good health.
Answer: Health can be defined as the state of complete physical, social and mental well-being.

• Availability of clean drinking water.
• Availability of sufficient and nutritious food.
• Social equality.
• Proper sanitation.

Question 125. What are intrinsic and extrinsic factors?
Answer: The disease-causing factors that are the components of our body are termed as intrinsic factors. The disease causing external agents, which enter our body from outside are called extrinsic factors.

Question 126. What do you understand by the term disease?
Answer: Disease is defined as an abnormal condition that disturbs or modifies the performance of vital functions of the body.

Question 127. Disease is defined as a ______ that disturbs or modifies the performance of vital functions of the body.
Answer. Abnormal condition

Question 128. What are the diseases caused by internal ­factors of the body?

1. Organic
2. Inorganic
3. Chronic
4. Acute

Answer. 1. Organic

Question 129. Which disease takes place in children with hyposecretion of thyroid?

1. Myxoedema
2. Cretinism
3. Exophthalmia goitre
4. Tetany

Answer. 2. Cretinism

Question 130. Find the odd one out from the following.

1. Scurvy
2. Beriberi
3. Anaemia
4. Haemophilia

Answer. 4. Haemophilia

Question 131. Which disease occurs due to the ­deficiency of protein?

1. Goitre
2. Bleeding disease
3. Marasmus
4. Beriberi

Answer. 3. Marasmus

Chapter 4 Why Do We Fall Ill Long Answer Type Question And Answers

Question 1. What are the diseases? Discuss the various factors which trigger disease.
Answer.

Diseases:

Disease is defined as an abnormal condition that disturbs or modifies the performance of vital functions of the body. Disease may result as a response to either of the following factors.

• Environmental factors: Industrial hazards, natural calamities and malnutrition.
• Infective agents: Worms, protozoan, bacteria, fungi and virus.
• Inherent defect of the organism: Genetic anomalies.

NEET Foundation Physics Chapter 4

Question 2. There are various modes of spreading the infection from an infected person to a healthy person. Discuss the direct and indirect methods of transmission. How sexually transmitted diseases are spread?
Answer.

There are various modes of spreading the infection from an infected person to a healthy person.

• Indirect transmission: It occurs when there is no direct human to human contact. The spreading of diseases is through air, water, vectors and contaminated surfaces and objects.
• Direct transmission: It occurs when there is a physical contact between the infected and susceptible person. It includes sexual contact, animal bites and contact with soil.

Syphilis, gonorrhoea and AIDS are some examples of sexually transmitted diseases. The pathogens for these diseases are transmitted through sexual intercourse between the two partners.

However, such sexually transmitted diseases are not spread by casual physical contact such as handshakes or hugs or sports, like wrestling or by any of the other ways in which we touch each other socially.

Read and Learn More NEET Foundation Long Answer Questions

Question 3. Discuss the principle of prevention of diseases and discuss how we can prevent the occurrence of diseases.
Answer.

The principle of prevention of diseases:

• Firstly, when someone is suffering from a disease, their body becomes weak and it takes time to recover completely.
• Secondly, the treatment takes time which means that someone suffering from a disease will have confined to bed till its convalescence.
• Thirdly, the individual suffering from an infectious disease may acts as a potent source to spread infection to other people or to the community.

There are various ways by which we can prevent the occurrence of disease and it is as follows.

• For airborne infection, we can prevent exposure by providing living conditions that are not overcrowded.
• For waterborne infection, we can prevent exposure by procuring clean drinking water.
• For prevention from vector-borne infections, clean environment is necessary. For example: Mosquito breeding can be stopped by ensuring cleanliness of water.

Question 4. Describe the symptoms and prevention of Hepatitis A and B.
Answer.

Symptoms and prevention of Hepatitis A and B:

Hepatitis A is an acute infectious disease of liver that affects both children and adult. Symptoms are high body temperature, headache, fatigue, joint paints, vomiting, nausea, loss of appetite, dark yellow skin and urine due to the presence of pigment named bilirubin and light coloured stool within 3–10 days of infection.

Prevention:

• Use of chlorinated, boiled or mineral water.
• Hands should be washed after cleaning the bed and vessels of the patients.
• Proper vaccination.

Hepatitis B: Hepatitis B is commonly known as ‘serum or transfusion’ hepatitis. This is the most fatal and common type of viral hepatitis among communities. The infection spreads through infected blood from mothers to their babies or by sexual routes. Symptoms are acute liver disease which turned to chronic one, hepatic carcinoma, liver cirrhosis, etc.

Prevention:

• Alcoholics or liquor should be avoided.
• Intercourse with more than one partner (promiscuous) should be avoided.

Question 5. What are the causative agent of tuberculosis and its symptoms?
Answer.

Causative agent of tuberculosis and its symptoms:

Tuberculosis is caused by Mycobacterium tuberculosis. Mycobacterium enters through respiratory tract and reaches various parts of the body, such as lungs, intestine and lymph glands. After entering the body, the bacteria release s a toxin called tuberculin. The chances of infection are increased when a person inhales the infected droplets through coughing, sneezing, spitting of the infected person.

Symptoms: The patient of tuberculosis feels sick and weak with a gradual loss of appetite and weight. The symptoms of tuberculosis depends upon the region where the pathogen is entering and the type of organ it is infecting.

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NEET Foundation Physics Chapter 4

Question 6. Explain the reasons for the following factors.

1. Balanced diet is necessary for maintaining healthy body.
2. Health of an organism depends upon the surrounding environmental conditions.
3. Our surrounding area should be free of stagnant water.
4. Social harmony and good economic conditions are necessary for good health.

Answer.

• Food is necessary for the growth and development of the body. Balanced diet provides raw materials and energy in appropriate amount needed for the substances, likes protein, carbohydrates, fats, minerals, etc., which in turn are essential for proper growth and functioning of the healthy body.
• Health is a state of being well enough to function well physically, mentally and socially and these conditions depend upon the surrounding environmental conditions. For instance, if unhygienic conditions prevail in the surrounding area, it is likely we might get infected or diseased.
• This is so because many waterborne diseases and insect vectors flourish in stagnant water which causes various diseases in human beings.
• Human beings live in societies and different localities like villages or cities, which determines the social and physical environment and hence, both are to be kept in harmony.
• Public cleanliness is important for individual health. For better living conditions, lot of money is required. We need good food for healthy body and for this we have to earn more money. And also for the treatment of diseases, one has to be in good economic condition.

Question 7. Explain why becoming exposed to pathogens or infected with an infectious microbe does not necessarily mean developing noticeable disease.
Answer.

Due to strong immune system, our body is normally fighting off microbes. We have cells which are specialized to kill the pathogenic microbes. These cells are active when the infecting microbes enter our body and if they are successful in removing the pathogen, we remain disease-free. So even if we are exposed to infectious microbes, it is not necessary that we suffer from diseases.

Question 8. Why are antibiotics not effective for viral disease?
Answer.

Antibiotics not effective for viral disease:

Antibiotics generally block the biosynthetic pathways and they block these pathways of the microbes/bacteria. However, viruses have very few biochemical mechanisms of their own and hence, they are unaffected by antibiotics.

Chapter 4 Why Do We Fall Ill Short Answer Type Question And Answers

Question 1. What are the different means by which infectious diseases are spread?
Answer.

The different means by which infectious diseases spread are as follows.

• Through air: They are also called airborne diseases. The air carries bacteria, virus and the diseases that can be caused are common cold, influenza, tuberculosis, etc.
• Through food and water: When one eats drinks contaminated food/water, that contains bacteria, virus, worm, etc., then it can cause diseases like cholera, typhoid, hepatitis, etc.
• Through contact: Many diseases spread through contact of infected person with the healthy person.
  Example: fungal infections, skin diseases, scabies, etc.
• By sexual contact: Many diseases can be transmitted, for example, syphilis, AIDS.
• By body fluids: Fluids like blood, semen, mother’s milk when infected can also cause diseases. Example: AIDS.
• Vectors: The organism that spreads a disease by carrying pathogens from one place to another is called vector. Example, mosquitoes are vectors that carry pathogens like protozoa.

Question 2. What is extrinsic factor in disease and also discuss the various factors?
Answer.

Extrinsic factor in disease:

These are the disease causing external agents, which enter in our body from outside. The various external factors involved are as follows.

• Insufficient diet or unbalanced diet: It makes a person unhealthy and prone to nutritional deficiency diseases.
• Various pathogenic agents like bacteria, fungi, virus and worms, etc.
• Environmental pollutants like oxides of carbon, sulphur and nitrogen, heavy metals like mercury, lead and arsenic, pesticides may also affect our health.
• Tobacco, alcohol and narcotic drugs may also contribute to ailments.

Question 3. What precautions can you take in your school to reduce the incidence of infectious diseases?
Answer.

The precautions that one takes in school to reduce the incidence of infectious diseases are as follows.

• By using handkerchief while coughing sneezing.
• Washing hands before eating breakfast or lunch.
• Staying at home if anyone suffers from infectious diseases.
• Getting vaccinated before the infection affects.
• Keeping the school surroundings clean, checking for stagnant water.

Read And Learn More NEET Foundation Short Answer Questions

Question 4. How are the congenital and acquired diseases are different from each other?
Answer.

Difference between congenital and acquired diseases

Question 5. What are waterborne diseases?
Answer.

Waterborne diseases:

Diseases can also spread through contaminated water. Cholera and typhoid are the prominent instances of waterborne diseases. This occurs when the excreta from someone suffering from an infectious disease, gets mixed with the drinking water used by people living nearby. The cholera causing microbes enter new hosts through water medium.

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Question 6. Discuss how vectors transmit diseases.
Answer.

Vectors transmit diseases:

Most of the diseases are transmitted by other animals. These agents carry the infecting agents from a sick person to another potential healthy host. These agents act as mediators in spreading infection and hence, they are called vectors. Vectors are also known as carrier of a disease.

The most common vectors we all know are mosquitoes. In many species of mosquitoes, the female anopheles needs highly nutritious food in the form of blood to lay mature eggs. Mosquitoes feed on many warm-blooded animals including humans transmitting diseases from person to person.

Question 7. Discuss the aims of ‘Pulse Polio Immunization Programme’.
Answer.

The aims of ‘Pulse Polio Immunization Programme’

• To immunize all the children below 5 years of age.
• To immunize those children who are not immunized earlier or partially immunized.
• To replace the disease causing wild virus by harmless vaccine virus in the environment.

Question 8. What are the symptoms and prevention of typhoid?
Answer.

Symptoms and prevention of typhoid:

Symptoms of the typhoid fever include continuous fever, headache with delirium (disorder of the mind), slow pulse, distended abdomen, watery stool and appearance of rashes on the body. Headache and fever reaches to its peak in the afternoon. The temperature rises each day in the first week and declines during the third or fourth day.

Prevention:

• Proper hygiene and sanitation.
• Disposal of faecal matter should not be avoided.
• TAB vaccination should be given as it provides immunity up to 3 years.

Question 9. What are the symptoms of malaria?
Answer.

Symptoms of malaria:

Symptoms include extreme cold, shivering, nausea, vomiting, headache, high fever, tachycardia, high respiration, muscular pain, and at the end extreme sweating occurs and body temperature comes to normal. In few cases, enlargement of spleen and liver is reported.

Question 10. What are the causative agent, control and prevention of AIDS?
Answer.

The causative agent, control and prevention of AIDS:

The causative agent is human immunodeficiency virus (HIV). No cure yet; a combination of drugs slows down the progress of the disease. Screening of blood donors, use of disposal needles and syringes, not sharing shaving blades and razors, safe sex practices.

Question 11. List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor. Why or why not?
Answer:

The three reasons why one would think that he is sick are (1) headache, (2) cold and cough, (3) dysentery. This indicates that there may be a disease but it does not indicate what the disease is. So, one would still visit the doctor for treatment to know the cause of above symptom. Even in case of single symptom one needs to visit the doctor to get proper treatment.

Question 12. Discuss how acute disease are different from chronic disease.
Answer:

Acute disease are different from chronic disease

Diseases such as common cold whose symptoms are rapidly visible is termed as acute disease. Chronic disease such as tuberculosis that are long-term and whose symptoms last for months or years are termed as chronic disease.

Question 13. Discuss the differences between infectious and non-infectious diseases.
Answer:

Differences between infectious and non-infectious diseases:

Question 14. Discuss the comparison of symptoms and signs of a disease.
Answer:

The comparison of symptoms and signs of a disease:

Question 15. What are congenital or inborn disease?
Answer:

Congenital or inborn disease:

Inborn diseases are present since birth. Acquired diseases are developed after birth. The main cause is due to genetic disorders. Hence, it is easily passed from one generation to the other.

Question 16. What is immunization?
Answer:

Immunization:

When the body attains immunity against any disease, due to vaccination. This process is called immunization.

Question 17. What are the various preventative measures adopted by your family when you fall sick? 
Answer:

various preventative measures adopted by our family when i fall sick

Basically, there are two ways to treat an infectious disease. One would be to reduce the effect of the disease and the other to kill the causative agent.

Question 18. What is vaccination?
Answer:

Vaccination:

Vaccination is the administration of antigenic material to stimulate an individual’s immune system to generate adaptive immune response against the pathogen.

Question 19. What are the immunization programs available at the nearest health centre in your locality? Which of these diseases are the major health problem in your area?
Answer:

The immunization programmes available at the nearest health care centres axe:

• Child immunization programme starts from 0 to 12 years.
• Polio eradication programme
• H1 N1 screening programme

Question 20. A doctor/nurse/health worker is exposed to more people than others in the community. Find out how she/he avoids getting sick herself/himself.
Answer:

A doctor/nurse/health worker when exposed to sick people they keep their nose and mouth covered, take care of hygiene, wash hands with soap before drinking water or eating food. They use mask, gloves, etc to avoid the direct contact with the person suffering from infectious diseases.

Question 21. Why are normally advised to take bland and nourishing when we are sick?
Answer:

We are advised to take bland and nourishing food when we are sick because our body needs energy to release cells to overcome the infection, the wear and tear of body organ. The nourishing food provides nutrients to our body that will further provide energy and make new cells. No spices in the food makes its digestion process faster, does not release acids in the body that can interfere in the treatment and cure.

Question 22. Which precaution can you take in your school to reduce the incidence of infectious diseases?
Answer:

The precautions that one can take care in school to reduce the incidence of infectious diseases are as follows.

• By using handkerchief while coughing and sneezing.
• Washing hands before eating lunch or breakfast.
• Staying at home if anyone suffers from infectious diseases.
• Getting vaccinated before the infection affects.
• Keeping the school surroundings clean, checking for stagnant water.

Question 23. What are infectious diseases?
Answer:

Infectious Diseases:

Infectious diseases are the diseases caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi.

Question 24. Why is it important to consider different kinds of infectious agents? 
Answer:

The answer lies within the mode of treatment to be chosen for the disease.

Question 25. How do infectious diseases spread?
Answer:

Infectious diseases spread as follows

Most of the microbes are transmitted from an affected person to an immunized person in a variety of ways. They can be ‘communicated’ from one person to other and so are called communicable diseases.

Question 26. Name the sexually transmitted diseases.
Answer:

Sexually transmitted diseases:

Syphilis, gonorrhoea and AIDS are some examples of sexually-transmitted diseases.

Question 27. Name the waterborne disease.
Answer:

Waterborne disease:

Cholera and typhoid are prominent instances of waterborne diseases.

Question 28. What are vectors?
Answer:

Vectors:

Vectors are also known as carrier of a disease. These agents act as mediators in spreading infection and hence, they are called vectors.

Physics Chapter 5 Sound

Sound

Sound is something we hear all the time around us, be it honking of cars on a busy road or chirping of birds in a serene landscape. It plays a major role in our lives where we receive and transmit sound for various purposes in our day-to-day life. Sound is a form of energy which propagates from one place to another through a medium. It is produced by bodies which vibrate. Consider a tuning fork ‘F’ which is excited by hitting on a rubber hammer.

When such a tuning fork is kept near our ears, we hear the sound but are unable to detect the vibrations of the tuning fork. When we speak, sound is produced by the vibration of vocal chords present in a cavity called larynx, in our throat. Sound is transmitted in the form of mechanical waves.

Thus, sound needs a medium to travel, since mechanical waves can propagate only through material medium.

In this chapter, we will learn more about sound and its propagation, its uses and its various forms in detail.

Chapter 5 Sound

Sound is a form of energy like heat energy, light energy, potential energy and kinetic energy. It causes a sensation of hearing in our ears. Sound cannot be created nor destroyed but can be changed from one form to another. For example, when we clap, a sound is produced.

Here, muscular energy is converted into sound energy. This is in accordance with the law of conservation of energy.

Read and Learn More: NEET Foundation Notes

Sound of various varieties is heard around us. We cannot see the sound but it travels in the form of waves and reaches our ears. These waves are formed due to vibrations of particles of the medium. Waves carry energy with them in the form of mechanical energy and produce a sensation of hearing in our ear.

Similarly, in an electric bell, when connected to electricity starts producing sound. Here, again electrical energy is converted into sound energy. Examples of sound discussed below.

1. Horn of a car
2. Alarm clock
3. Music
4. Human voice
5. Barking of dogs
6. Hand clapping

Sound can be described in two different ways.

1. Subjective or psychological sound, which refers to hearing sensation which ceases when the sound sensing organ is withdrawn from the scene.
2. Objective or physical meaning refers to the energy reaching the ear from outside. The energy continues to propagate even if no ear is present to detect it.

Chapter 5 Sound Production of Sound

Physics of sound

Sound is produced when an object vibrates. Now, what is vibration? Vibration is the rapid to and fro motion of an object. The motion of materials or objects causes vibration. To understand it better let us illustrate some examples.

Example 1: Take a guitar and pluck its string at the centre . Now pluck it at the centre. It will start vibrating and you can hear a sound. After few minutes, string will stop vibrating and sound will also stop as well.

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Example 2: Take a U shaped fork. Hang a ball with a thread. Now strike the ball and bring the vibrating tuning fork near the ball. You will hear the sound of the vibrating tuning fork. As soon as the arm of the fork stops vibrating, the ball will also stop oscillating and there will be no sound.

These examples show that sound is produced when an object vibrates and it stops when the object stops vibrating.

As we said abovem sound is a form of energy. Let us elaborate it further. Mechanical energy is required to start vibrations in an object producing sound. The vibrations of object are transmitted in a medium in waveforms from one point to the next and so on.

These waves on reaching our ears produced vibrations in the eardrum which are perceived as sound by us. Thus, sound is a form of energy.

Chapter 5 Sound Propagation of Sound

The vibrating object produces sound thattravels through a medium to reach the ­listener. The medium through which sound travels can either be solid, liquid or a gas. When an object vibrates, it creates a periodic disturbance in the nearby medium.

The particles around the medium also start vibrating. As a result of it, the particles in contact with the vibrating object is first displaced from its equilibrium position. It then exerts a force on the adjacent particle and the adjacent particle is displaced from its position of rest.

After displacing the adjacent particle the first particle comes back to its original ­position. This process gets repeated in the medium till the sound reaches the listener.

Therefore, the disturbance moves forward in the form of compression. The particles of the medium do not move with the compression.

Sound Wavelength

Sound Needs Medium to Travel

Amedium is necessary forthe propagation of sound from one place to another. The matter or substance through which sound is transmitted is called a medium. The medium can be solid, liquid, or gas. Sound cannot travel in vaccum. A true vaccum refers to the complete absence of matter.

Sound waves can travel only through matter. So, sound needs a physical medium in order to travel anywhere. A vibrating object travels from one place to another through the mechanical vibrations of medium particles in the form of waves.

Activity to Show that Sound Needs a Material Medium for its Propagation

Take an electric bell and suspend it inside an air tight glass bell jar. Connect the bell jar to a vacuum pump. When the key is pressed, the circuit of electric belt is complete. The hammer of the electric bell begins to strike the gong repeatedly due to which sound is heard. Now keeping the key pressed, air is gradually with drawn from the jar by starting the vacuum pump.

It is noticed that the loudness of sound goes on decreasing as the air is removed from the bell jar and finally no sound is heard when all the air from the jar has been drawn out. The hammer of the electric bell is still seen striking the gong repeatedly which means that sound is still produced, but it is not heard.

Illustration

When hammer of the bell hits the gong, sound is produced due to vibrations of gong which travels through air to the wall of jar. This causes the wall of jar to vibrate and the air outside the jar is also set in vibration. Therefore, we can hear the sound.

But when hair has been removed from the jar, sound produced due to vibration of gong could not travel to the wall of jar, so wall could not vibrate, hence no sound is heard. This clearly demonstrates that sound requires a material medium for transmission and it cannot travel through vacuum.

Requisites of the Medium

The medium required for propagation of sound must have the following properties:

1. The medium must be elastic so that its particles may come back to their initial positions after displacement on either side.
2. The medium must have inertia so that its particles may store mechanical energy.
3. The medium should be frictionless so that there is no loss of energy in propagation of sound through it.

We know sound can propagate in all states, i.e., solid, liquid and gas. Some materials like water, air, etc., can easily transmit sound from one place to another while on the other hand materials like blanket, thick curtains, etc., transmit only a small fraction of it because it absorbs most of the sound incident on them.

Sound Propagates as Waves

Sound propagates from one place to another in the form of waves, i.e. because of the disturbances of particle of the medium. Wave is a phenomenon or disturbance in which energy is transferred from one point to another without any direct contact between the points. So, sound is considered as a wave. Particle of medium only vibrate. They do not move from one point to another.

On the basis of direction of propagation, waves can be divided into two types – (a) longitudinal waves and (b) transverse waves

Longitudinal Waves

A wave in which particles of the medium vibrate about their mean positions, in the direction of propagation of the wave is called longitudinal wave (Fig. 5.5). Sound travels in air in the form of longitudinal waves. Longitudinal waves can be produced in all forms, i.e., solid, liquid and gas. At compressions, the density and pressure of the medium are maximum, while at rarefaction the density and pressure of the medium are minimum.

Compression and Rarefaction

Air is the most common medium through which sound travels. When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called compression. It is represented by the symbol C.

When the vibrating object moves backwards, it creates a region of low pressure called rarefaction. It is represented by the symbol R.

In the we see that waves are formed when a stone is dropped on the still water surface. Along with waves we also hear sound of stone as the stone strikes the water surface. This is due to the disturbance produced in water. The disturbance spreads in all directions rapidly outwards in the form of circular waves on the surface of water.

Now keep a small paper boat on the water surface at some distance away from the point where the stone strikes, we notice that the ball doesn’t move ahead, instead it will vibrate in the up and down direction as the wave moves ahead. The reason behind this is that the particles of water start vibrating up and down at the point where the stone strikes.

These particles then transfer their energy to other neighbouring particles and they themselves come back to their mean positions. This process continues and thus the disturbance moves ahead on the water surface in the form of waves. The waves die out as soon as the energy imparted by the stone gets dissipated.

Transverse Wave

A wave in which the particles of the medium vibrate about their mean positions, in a direction perpendicular to the direction of propagation of the wave is called a transverse wave.

Transverse wave is composed of:

1. Crest: The position of maximum upward displacement is called crest.
2. Trough: The position of maximum downward displacement is called trough.

Comparison between transverse and longitudinal waves

Progressive and Stationary Waves

There are some waves that start at the point of origin of the waves and progress endlessly into other parts of the medium. Such waves are known as progressive waves.

Consider a progressive transverse water wave moving from left (point P) to right and striking a hard surface at ‘Q’and is called an ‘incident wave’. It then gets reflected at ‘Q’, and travels towards ‘P’. Thus the two waves, one going from ‘P’ to ‘Q’ and the other going from ‘Q’ to ‘P’ called the ‘reflected wave’ overlap resulting in the formation of ‘nodes’ and ‘antinodes’.

Points, where the displacement of a vibrating particle of the medium is zero or minimum are called ‘nodes’ and points, where the displacement of the vibrating particles is maximum are called ‘antinodes’. The closed ­figures so formed are called ‘Loops’.

These loops are On the whole, the wave appears to be stationary or standing, contained between two positions ‘P’ and ‘Q’ and so called as ‘stationary waves’ or ‘standing’. Thus a ‘progressive wave is a wave which is generated at a point in a medium and travels to all parts of the medium infinitely carrying the energy’ and a ‘stationary wave is a wave which is formed by a superposition of two identical progressive waves traveling in opposite directions’.

Comparative study of progressive and stationary waves

Characteristics of Wave Motion

1. A wave is produced by the periodic disturbance at a point in the medium.
2. Due to propagation of a wave in a medium, the particles of the medium vibrate about their mean positions and energy is transferred with a constant speed from one place of medium to the other.

Characteristics of Sound Wave

Sound can be described in terms of the following physical quantities:

1. Amplitude: The maximum displacement of the particle of a medium on either side of its mean position is called amplitude of the wave. It is denoted by the symbol ‘A’. S.I. Its unit is metre (m).

2. Time period: The time taken by a particle of the medium to complete its one ­vibration is called time period of the wave. It is denoted by the letter T. Its S.I. unit is second (s).

3. Frequency: The number of vibrations made by a particle of the medium in one second is called frequency of wave.

Another definition is number of waves passing through a point in one second.

It is denoted by the symbol n, f, neu (υ)

Its S.I. unit is hertz (Hz) or s^-1.

Relation:

υ = 1/T

where υ = frequency, T = time period.

The frequency of a wave is equal to the frequency of vibrations of its source. It is the characteristic of its source which produces the disturbance. It does not depend on the amplitude of vibration or on the nature of medium in which the wave propagates.

4. Wavelength: The distance travelled by the wave in the time period of vibration of particles in the medium is called its wavelength. It is denoted by the letter λ (lambda). Its S.I. unit is metre (m). It depends on the medium in which the wave travels.

In a longitudinal wave, the distance between two consecutive compressions or two consecutive rarefactions is equal to one wavelength.

In a transverse wave, the distance between two consecutive crests or between two consecutive troughs is equal to one wavelength.

5. Wave velocity: The distance travelled by a wave in one second is called its wave velocity. It is the velocity with which energy is transferred from one place to another by wave motion. It is not the velocity of an individual particle vibrating about its mean position.

Wave velocity is constant for a given medium. It depends on the elasticity and the density of the medium. It changes when same wave passes from one medium to the other medium. It is denoted by the letter v. Its S.I. unit is m/s.

Displacement–Time Graph

The above graph shows the variation of displacement of a certain particle of the medium with time, when a wave propagates through it. It is called displacement–time graph.

Displacement–Distance Graph

The above figure shows the displacement–distance graph of a transverse wave at an instant. It is a snapshot of a wave. Distance AE or CG gives us the wavelength (λ) of the wave.

Relationship between Wavelength, Wave Velocity and Frequency

Let velocity of wave = v

Time period = T

Frequency = υ

Wavelength = λ

As per the definition of wavelength,

λ = Distance travelled by wave in one time period

= Wave velocity × Time period

= v × T

vT = λ

T = 1/υ

v × (1/υ) = λ

Therefore,

v = λυ

Hence,

Wave Velocity = Frequency × Wavelength.

Speed of Sound in Different Media

Sound travels in a medium with a finite speed and it takes some time to reach a destination from the source.

The speed of sound in a medium depends on the following factors:

1. Elasticity of (E) of the medium
2. Density (r) of the medium

The speed of sound in a medium is given by the formula

v = \(\sqrt{\frac{E}{\rho}}\)

where E is the modules of elasticity and ρ is the density of medium.

Sir Isaac Newton assumed, when sound travels in a gas, temperature of the gas does not change. In other words, the propagation of sound is an isothermal change. For isothermal change, modulus of elasticity is equal to the pressure of the gas, i.e. E = P.

Therefore, velocity of sound in gas was given by

v = \(\sqrt{\frac{P}{\rho}}\)

The expression given by Newton for the velocity of sound in a gas medium, later was modified by Laplace, where he introduced ‘γ ’, as a constant for a given gas. It is defined as the ratio of the specific heat capacity of the gas at constant pressure to its specific heat capacity at constant volume.

Types of sound

Therefore, v = \(\sqrt{\left(\frac{\gamma P}{d}\right)}\), where, ‘γ ’(gamma) is a constant.

The speed of sound is different in different media. It is more in solids, less in liquid and least in gas. This is because solids are much more elastic than the liquids and gases. The speed of sound is nearly 5100 m/s in steel, 1450 m/s in water and 330 m/s in air at 0 °C. Table 5.3 below gives the speed of sound in different media at 0 °C.

Speed of sound in different media

Example: If sound is produced at one end of a very long steel bar, two sounds are heard at the other end. One which reaches first is propagated through steel and the other which is heard later is through air.

Factors Affecting the Velocity of Sound in a Air

The speed of sound in a gas is affected by

1. Effect of density: As we know v = \(\sqrt{\frac{\gamma P}{\rho}}\), it shows that \(v \propto \frac{1}{\sqrt{\rho}}\)

The speed of sound is inversely proportional to the square root of density of the gas.

The density of oxygen is 16 times the density of hydrogen; therefore the speed of sound in hydrogen is four times the speed of sound in oxygen other factor being same.

2. Effect of temperature: The speed of sound in a gas increases with the increase in the temperature of the gas. This is because with the increase of temperature, density of gas decreases and consequently the speed of sound increases.

Speed of sound is directly proportional to the square root of temperature of medium.

\(V \propto \sqrt{T}\) , where T is the temperature of the gas on the Kelvin scale.

The speed of sound in air increases by about 0.61 m/s for each degree celsius rise in its temperature.

V_t = V₀ + 0.61 t

where ‘t’ is temperature of air in °C.

3. Effect of humidity: The speed of sound in air increases with the increase in humidity in air.

The density of water vapour is about 5/8th times the density of dry air at ordinary temperatures, therefore the increase of moisture in air tends to decrease the density of air. This is the reason why the speed of sound in the humid air is greater than the speed of sound in the dry air.

4. Effect of direction of wind: The speed of sound increases or decreases according to the direction of wind. If wind is blowing in the direction of propagation of sound, the speed of sound increases but if it is flowing in the direction opposite to that of sound, then speed of sound will decrease.

If v is the speed of sound in still air and W is the speed of wind, the speed of sound becomes v + W when wind blows in the direction in which sound travels and the speed of sound becomes v – W when wind blows in direction opposite to the direction in which sound travels.

Factors not Affecting the Velocity of Sound in a Air

The velocity of sound in air is not affected by the change in

1. Wavelength (λ): The velocity of sound in air or any other medium does not depend on its wavelength (λ).
2. Frequency (n): The velocity of sound in air or any other medium does not depend on its frequency.
   We know that v = nλ. As the frequency (n) increases, its wavelength (λ) decreases but does not affect the velocity of the wave.
3. Amplitude: Velocity of sound does not depend on the amplitude of the vibrations.
4. Pressure: The velocity of sound in air or any gas in given by v = \(\sqrt{\frac{\gamma P}{d}}\); where ‘γ ’ is a constant, ‘P’ is the pressure and ‘d’ is the density.
   When the pressure of a gas is changed, its density also changes such that the ratio ‘P’/d is always a constant. Therefore, the variation of pressure of a gas does not affect the velocity of sound in it.

Comparison of Speed of Sound with Speed of Light

• The light can travel in vacuum but sound cannot.
• The speed of light in air is 3 × 10⁸ m/s which is about a million times greater than the speed of sound in air. (i.e. 330 m/s at 0 °C).
• The speed of light decreases in an optically denser medium while the speed of sound is more in solids, less in liquids and least in gases.
• In thunder, light is seen much earlier than sound of thunder is heard, even though they are produced simultaneously.
• In an athletic event, when the starter fires a gun, the sound of fire is heard a little later while the smoke is instantaneously seen. The reason is that v_light > V_sound .

Characteristics of Sound as we Hear It

1. Loudness: Loudness of sound is the measure of sound energy reaching the ear per second. Loudness or softness of a sound wave is the sensation that depends upon its amplitude.

E.g. When we strike the top of a table with more force, it vibrates and produces a loud sound. But, when we strike the top of table with lesser force, the vibrating table top produces soft sound waves. Louder sound has more amplitude.

2. Pitch: When a guitar n flute are played together then the sound emitted by the two musical instruments are different. The difference is due to one more characteristic of sound namely pitch.

Pitch is the sensation (brain’s interpretation) of the frequency of an emitter sound. The pitch of sound (Shrillness or flatness) depends on the frequency of vibration.

Faster the vibration of the source, higher is the frequency and higher the pitch and vice versa, Similarly, low pitch sound corresponds to low pitch.

3. Quality or Timbre: Quality or timbre of sound wave is that characteristic which helps us in distinguishing between two sounds of same loudness and same pitch.

Music and Noise

1. Music is the sound that is pleasant to hear/to the ears (e.g, sound coming out of musical instruments)
2. Noise is the sound that is unpleasant to hear/the ears (E.g., Sound produces by vehicles)

Tone and Note

1. A pure sound of single frequency is called tone.
2. An impure sound produced by mixture of many frequencies is called a note. It is pleasant to hear.

Sonic Boom: Speed of sound in air is 333 m/s, speed of faster runner = 12.5 m/s. Many objects such as aircrafts, bullets, and rocket planes travel at speed greater than the speed of sound in air. Such objects are said to be travelling with supersonic speed.

1. Objects moving with speed greater than speed of sound is said to have supersonic speed.
2. Supersonic aircraft produces shock waves in air due to its very high speed. The air pressure variation associated with shock waves produces a very sharp and loud sound called “Sonic boom”.

Chapter 5 Sound Reflection of Sound

Sound waves and music

Sound gets reflected at the surface of solid and liquid in the same way as light does. It follows the law of reflection. Bouncing back of sound wave from the surface of a solid or a liquid is called reflection of sound.

1. The laws of reflection are as follows:
2. The angle of incidence is equal to the angle of reflection.

The incident ray, reflected ray and normal at the point of incidence, they all lie in the same plane.

we have taken two identical cardboard tubes and arrange them as shown in the figure near the hard plywood. At one end of the cardboard, put in an alarm clock. Now try to listen to the clock tick-tock from the other by adjusting the position of the cardboard. Now measure the angles of incidence and reflection. Now lift the second pipe and try to hear the sound.

In this experiment you will notice that the angle of incidence is equal to the angle of reflection. Incident ray, reflected ray and normal all lie in the same plane.

Instead of hard plywood we can use any obstacle of big size which is either polished or rough. This is used for the reflection of sound waves.

Echo

The sound that comes to our ear after reflection is called echo or echo of sound.

Examples

1. Sound we hear after clap is an echo.
2. Sound heard after shouting in a big empty hall is also an echo.

The sensation of sound remains in human brain for about 0.1 s. It means the time interval between the original sound and echo must be at least 0.1 s. At times echo is heard multiple times. This happens when there is successive or multiple reflections. For example, thunderstorm.

As we know the speed of sound in air is 344 m/s. The distance travelled by sound in 0.1 s will be

D = v × T

= 344 × 0.1

= 34.4 m

It means to hear the echo properly, the minimum distance of the reflecting surface should be half of this distance, i.e. 34.4/2 = 17.2 m.

Temperature has impact on echo. So when temperature changes, distance will also change.

Reverberation

When echo is heard multiple times due to repeated and multiple reflections of sound from different reflecting surfaces, it causes persistence of sound. This is called reverberation.

Example: Sound echoes multiple times, when a man shouts at a top of the mountain cliff.

At places like auditorium, big halls sound echoes multiple times. To reduce ­reverberation, roofs and walls are covered by sound absorbing materials. These can be rough plaster, draperies or compressed fibre board. Reverberation can be prevented by stopping the reflection of sound. This could be done by:

• Using soft sound absorbent material, such as curtains, plant fibres, compressed fireboard, carpets are used in big halls.
• These materials absorb undesired reflected sound and reduce reverberation.

Uses of Multiple Reflection of Sound

On one hand reflection of sound can be irritating but on the other side it proves to be helpful. Let us see some examples where reflection of sound is useful.

1. Loudspeaker, Megaphone, Bulb horn: Devices like loudspeaker, megaphones are designed in such a way that they send the sound in a particular direction by multiple reflections without deviating it into various directions.

2. Soundboard: Soundboard is used in big halls or auditoriums where sound is sent towards auditorium. It works on the basis of law of reflection of sound waves.

Soundboard is a big concave board and it is placed behind the stage in such a manner that it focuses the speaker. Sound that is coming from the speaker falls on the soundboard which in turn gets reflected towards the audience. The result of this is that the audience who are sitting far from the speaker can ­easily hear the sound that is coming out from the speaker.

The walls of auditorium are also constructed in the form of curve. Hence, ceiling acts like a soundboard.

3. Stethoscope: Stethoscope is an instrument used by doctors for listening human breath. In stethoscope, human body’s sound is received by chest piece which is sent to ear by multiple reflections done inside the long tube.

Use of Multiple Reflection of Sound

• Measuring the depth of sea or ocean.
• Used for the detection of the position of objects. For example, sea rocks, hidden ice-berg in the sea and ocean shipwrecks.
• Investigating problem inside the human body.

 

Chapter 5 Sound Range of Hearing

The human ear is able to hear sound in a frequency range of about 20 Hz to 20,000 Hz. In other words the audible range of frequency is 20 Hz to 20 kHz. Any sound out of this range is called not audible.

The audible range of frequency varies from person to person and it also varies with age of the person. As the person grows older, his hearing power decreases.

Children can hear higher frequencies of up to 30 kHz while an old person can hear up to 12 kHz. Therefore, on an average the audible range is from 20 Hz to 20 kHz.

The human ear is most sensitive in the range 2 kHz to 3 kHz, where it can hear even a very feeble sound. Unlike human, animals can hear sounds of frequency below 20 Hz and above 20 kHz. Different animals have different range of frequency. Frequency ranges for hearing and speaking by humans and animals.

Let us see the frequency ranges for hearing and speaking of various animals and human.

Chapter 5 Sound Ultrasound and Its Applications

As studied in the last topic, the frequency of sound above 20 kHz is called ultrasound. Ultrasound can travel freely in solids and liquids. In case of gases, its intensity falls. In the medium, the speed of ultrasound is same as that of audible sound. In air, the speed of ultrasound is 330 m/s.

Properties of Ultrasound

Ultrasound has all the properties that an ordinary sound has. But because of its high frequency it has two additional properties.

• The energy carried by ultrasound is very high.
• The ultrasound can travel along a well-defined straight path. It does not bend appreciably at the edges of an obstacle because of its small wavelength.
  The above properties of ultrasound make it very useful for different purposes. It is extensively used in industries and for medical purposes.

Applications of Ultrasound

Some applications of ultrasound are given below:

• Bats avoid obstacles in their path by producing and hearing the ultrasound. They emit ultrasound which returns after striking an obstacle in their way. By hearing the reflected sound and from the time interval, they can judge the direction and the distance of the obstacle in their way.
• Ultrasound is used for drilling holes or making cuts of desired shape in materials like glass.
• It is used for cleaning very small objects like cleaning parts of watches or other electronic items. The objects are placed in the cleaning solution and ultrasonic waves are passed in the solution. This causes high frequency vibrations in the solution and makes the cleaning easier.
• Ultrasound is used for detection of defects in metals. Ultrasound will pass through the object if there is no defect but if there is some defect, ultrasound will get reflected back.
• Ultrasound is widely used for imaging the human organs. Ultrasonography is used to obtain the images of patient’s organs such as liver, gall bladder, uterus, etc. It helps to detect stone, tumour, etc. Echo cardiology is used to obtain the image of the heart.
• Ultrasound is used in surgery to remove cataract and in kidneys to break the stone in fine grains.
• In SONAR (abbreviated form of sound navigation and ranging) to detect and find the distance of objects under water, ultrasound is used.

Infrasonics or Infrasound

Infrasonic waves are the waves which has frequency less than 20 Hz. These waves are produced by large vibrating bodies. For example they are produced by the vibration of the earth’s surface during the earthquake.

These waves are also produced by some animals like elephants, rhinoceroses, whales, etc. These waves are not audible to human ears.

It has been observed that the animal’s behaviour becomes unusual just before tremor is felt. This is because the animals have the ability to detect infrasonic waves produced at the time of tremor.

Sound Navigation and Ranging (SONAR)

SONAR is a device which is used in the ships to locate rocks, icebergs, and submarines, old sank in seas etc.

Ultrasonic waves of high frequency are sent from a ship on the surface. The waves travel in straight line till they hit somebody like shipwreck or submarine. On hitting the body these waves are reflected back as shown in figure.

The transmitter sending the wave notes the time t between sending the signal and receiving it back. Let if d is the distance of the submarine from the ship, than the total distance travelled by the wave in time interval t is 2d.

\(\text { Using speed }=\frac{\text { Distance }}{\text { Time }}\)

v = \(\frac{2 d}{t}\)

Therefore d = \(\frac{1}{2}(v \times t)\)

The velocity v of the ultrasonic wave in water is same as that of audible range of water.

Chapter 5 Sound Structure of Human Ear

Ear acts as a receiver or detector of sound. The sound that is received in the form of pressure variations in air are converted into electrical signals within the ear. This sound on reaching our brain produces a sense of hearing. The human ear consists of three parts:

1. Outer ear: The outer ear looks complicated but it is functionally the simplest part of the ear. It consists of the ‘pinna’ or auricle (the visible projecting portion of the ear), the external acoustic meatus (the outside opening to the ear canal), and the external ear canal that leads to the ear drum. In sum, there is the pinna, the meatus and the canal. That’s all. The outer ear concentrates air vibrations on the ear drum and makes the drum vibrate. The outer ear is also called external ear.

2. Middle ear: The middle ear consists of an eardrum or tympanic membrane connected at the end of the auditory canal. The eardrum is a thin, tightly stretched membrane, also known as sheet (‘kaan ka parda’ in Hindi). The eardrum vibrates when compressions and rarefactions of sound wave hit it. A compression exerts an inward pressure on the outer surface of the eardrum. This forces the eardrum to move inward. However, a rarefaction does the opposite and moves the eardrum outwards.

Hence, the eardrum is made to vibrate by the successive compressions and rarefactions. The vibration of eardrum produces pressure variations within the middle ear. The three bones (hammer, anvil and stirrup) present in the middle ear amplify these pressure variations several times. The middle ear then transmits the sound wave’s amplified pressure variations to the inner ear.

3. Inner ear: The inner ear has a job to convert the sound wave’s amplified pressure variations into electrical signals. This work is done in the inner ear by cochlea, a snail-shaped organ. The cochlea is filled with water like fluid and its inner surface has large number of hair-like nerve cells.

The amplified pressure variations produce vibrations in the nerve cells and they in turn release electrical impulses. The electrical impulses are transmitted to the brain along the auditory nerve. The brain interprets the electrical impulses through a complex process, as sounds.

Chapter 5 Sound Fill in the Blanks

Question 1. Sound shows______variation with temperature.
Answer. Speed

Question 2. Infrasonic sound has less ______.
Answer. Frequency

Question 3. 1 kHz = ______Hz
Answer. 1000

Question 4. The maximum displacement of a wave from its mean position is known as ______.
Answer. Amplitude

Question 5. Wavelength is denoted by the symbol ______.
Answer. λ

Question 6. _____ is the unit of loudness of sound.
Answer. Decibel

Question 7. Echo is observed usually in ______ rooms.
Answer. Large

Question 8. In SONAR, ‘S’ stands for ______.
Answer. Sound

Question 9. In order to distinguish between two different sounds, they must be heard after an interval of ______.
Answer. 0.1 s

Question 10. If the time period is 0.05 second, then the frequency is ______ Hz.
Answer. 20

Question 11. _______________ is required to start vibrations in an object producing sound.
Answer. Mechanical energy

Question 12. Sound is a form of _________________.
Answer. Energy

Question 13. ______ acts as a receiver or detector of sound.
Answer. Ear

Question 14. The ______ vibrates when compressions and rarefactions of sound wave hit it.
Answer. Eardrum

Question 15. The ______ has a job of converting the sound wave’s amplified pressure variations into electrical signals.
Answer. Inner ear

Chapter 5 Sound Match the Columns

Question 1. Choose the correct speed (m/s) of substance at temperature 25 °C.

Select the correct option:

1. A-1, B-2, C-3, D-4
2. A-4, B-3, C-2, D-1
3. A-2, B-1, C-3, D-4
4. A-1, B-2, C-4, D-3

Answer. 2. A-4, B-3, C-2, D-1

Question 2. Choose the correct S.I. unit.

Select the correct option:

1. A-1, B-2, C-3, D-4
2. A-4, B-3, C-2, D-1
3. A-2, B-1, C-3, D-4
4. A-4, B-1, C-2, D-3

Answer. 4. A-4, B-1, C-2, D-3

Question 3. Choose the correct symbol.

Select the correct option:

1. A-1, B-2, C-3, D-4
2. A-2, B-4, C-1, D-3
3. A-2, B-1, C-3, D-4
4. A-4, B-1, C-2, D-3

Answer. 2. A-2, B-4, C-1, D-3

Question 4. Choose the correct code.

Select the correct option:

1. A-1, B-2, C-3, D-4
2. A-2, B-4, C-1, D-3
3. A-2, B-1, C-3, D-4
4. A-4, B-1, C-2, D-3

Answer. 2. A-2, B-4, C-1, D-3

Chapter 5 Sound Assertion Reasoning

Direction: For the following questions the options will remain the following:

1. Both A and R are correct and R is correct explanation of A.
2. Both A and R are correct but R is not a logical explanation of A.
3. A is correct but R is incorrect.
4. R is correct but A is incorrect.

Question 1. Assertion: A boy shouts near mountain, he hears his sound again.
Reason: This is because of the reflection of sound.
Answer. 1. 1. Both A and R are correct and R is correct explanation of A.

Question 2. Assertion: Ultrasonic sound is used to clean electronic components.
Reason: Due to low frequency, dirt particles get detached from the components.
Answer. 2. Both A and R are correct but R is not a logical explanation of A.

Question 3.Assertion: The ceilings of concert halls and conference halls are made curved.
Reason: This way sound wave reaches all thepart after reflection from the curved surface.
Answer. 1. Both A and R are correct and R is correct explanation of A.

Chapter 5 Sound Multiple Choice Question And Answers

Direction: Choose the correct option for each question. There is only one correct response for each question.

Question 1. In SONAR, ______ waves are used.

1. Ultrasonic
2. Infrasonic
3. Radio
4. Audible sound

Answer. 1. Ultrasonic

Question 2. When we change feeble sound to loud sound we increase its ______.

1. Velocity
2. Wavelength
3. Frequency
4. Amplitude

Answer. 4. Amplitude

Question 3. Infrasound can be heard by which animal?

1. Human beings
2. Rhinoceros
3. Bat
4. Dog

Answer. 2. Rhinoceros

Question 4. Sound waves in the air are ______.

1. Radio waves
2. Electromagnetic waves
3. Longitudinal waves
4. Transverse waves

Answer. 3. Longitudinal waves

Read and Learn More NEET Foundation Multiple Choice Questions

Question 5. The unit of quantity on which the loudness of sound depends is ______.

1. Metre
2. Second
3. Hertz
4. m/s

Answer. 1. Metre

Question 6. Sound travels faster in ______.

1. Solid
2. Liquid
3. Gas
4. None of the above

Answer. 1. Solid

Question 7. S.I. unit of frequency is ______.

1. Metre
2. Second
3. Hertz
4. m/s

Answer. 3. Hertz

Question 8. The distance between two consecutive crests or two consecutive troughs is called ______.

1. Velocity
2. Wavelength
3. Frequency
4. Amplitude

Answer. 2. Wavelength

Question 9. ______ is produced with the vibration of objects.

1. Sound
2. Wavelength
3. Frequency
4. Amplitude

Answer. 1. Sound

Question 10. Sound is the form of ______.

1. Force
2. Energy
3. Heat
4. Speed

Answer. 2. Energy

Question 11. Which among the following equation is correct?

1. Wave Velocity = Frequency × Wavelength
2. Frequency = Wavelength × Wave Velocity
3. Wave velocity = frequency/wavelength
4. Wavelength = frequency/wave velocity

Answer. 1. Wave Velocity = Frequency × Wavelength

Question 12. The speed of sound in air is ______ at 0 °C.

1. 330 m/s
2. 331 m/s
3. 332 m/s
4. 334 m/s

Answer. 2. 331 m/s

Question 13. A sound wave travels from east to west then particles of air will move in ______ direction.

1. East–West
2. West–East
3. North–South
4. South North

Answer. 1. East–West

Question 14. The frequency ranges for hearing and speaking of dog is ______.

1. 20 Hz – 20 kHz
2. 50 Hz – 50 kHz
3. 60 Hz – 50 kHz
4. 20 Hz – 50 kHz

Answer. 4. 20 Hz – 50 kHz

Question 15. The frequency of sound above 20 kHz is called ______.

1. Ultrasound
2. Infrasound
3. Ultrasand
4. Infrasonic

Answer. 1. Ultrasound

Question 16. The minimum distance between the source and the reflector so that the echo is heard is approximately equal to ______ m.

1. 10
2. 13
3. 17
4. 20

Answer. 3. 17

Question 17. Choose the correct relationship between wave velocity (v), frequency ( f) and wavelength (λ). 

1. V = fλ
2. V = f/λ
3. V = λ/f
4. V = 1/f λ

Answer. 1. V = fλ

Question 18. Which of the following is not the characteristic of a musical sound?

1. Quality
2. Wavelength
3. Pitch
4. Loudness

Answer. 2. Wavelength

Question 19. We cannot hear sound on the moon because sound does not travel in ______.

1. Solid
2. Liquid
3. Gas
4. Vacuum

Answer. 4. Vacuum

Class 11 Physics	Class 12 Maths	Class 11 Chemistry
NEET Foundation	Class 12 Physics	NEET Physics

Question 20. The physical quantity that oscillates in most waves is ______.

1. Energy
2. Mass
3. Amplitude
4. Wavelength

Answer. 3. Amplitude

Question 21. ______ remains unchanged when a sound wave travels in air or in water.

1. Frequency
2. Amplitude
3. Wavelength
4. Speed

Answer. 1. Frequency

Question 22. The frequency which is not audible to the human ear is ______.

1. 50 Hz
2. 500 Hz
3. 5000 Hz
4. 50000 Hz

Answer. 4. 50000 Hz

Question 23. Sound and light waves both ______.

1. Have similar wavelength
2. Follow the law of reflection
3. Travel through vacuum
4. Travel as longitudinal waves

Answer. 2. Follow the law of reflection

Question 24. The technique used by bats to find their way or to locate food is ______.

1. Flapping
2. SONAR
3. RADAR
4. Echolocation

Answer. 4. Echolocation

Question 25. Which among the following is an example of mechanical wave?

1. Sound wave
2. Radio wave
3. Light wave
4. Infrared wave

Answer. 1. Sound wave

Question 26. Which of the following quantities is transferred during wave propagation?

1. Speed
2. Velocity
3. Acceleration
4. Energy

Answer. 4. Energy

Question 27. ______ is the unit of wavelength.

1. Newton
2. Dyne
3. Erg
4. Angstrom

Answer. 4. Angstrom

Question 28. The S.I. unit of time is ______.

1. Nanosecond
2. Second
3. Minute
4. Hour

Answer. 2. Second

Question 29. The persistence of audible sound due to the successive reflections from the surrounding objects even after the source has stopped to produce that sound is called ______.

1. Echo
2. Reflection
3. Reverberation
4. Rarefaction

Answer. 3. Reverberation

Question 30. Vibrations inside the ear are amplified by three bones namely the ______ in the middle ear.

1. auditory bone, anvil and stirrup
2. hammer, cochlea and stirrup
3. hammer, anvil and stirrup
4. hammer, anvil and pinna

Answer. 2. hammer, cochlea and stirrup

Question 31. The ceilings of concert halls and conference halls are made curved because ______.

1. This way sound waves reaches all the part after reflection from the curved surface
2. This way sound does not become distorted and confusing
3. This way reverberation is avoided
4. All of the Above

Answer. 1. This way sound waves reaches all the part after reflection from the curved surface

Question 32. Note is a sound ______.

1. of mixture of several frequencies
2. of mixture of 2 frequencies only
3. of a single frequency
4. always unpleasant to listen

Answer. 1. of mixture of several frequencies

Question 33. The vibrations or the pressure variations inside the inner ear are converted into electrical signals by the_____.

1. Anvil
2. tympanic membrane
3. pinna
4. cochlea

Answer. 4. cochlea

Question 34. The distance between a compression and the next rarefaction of a longitudinal wave is ______.

1. λ
2. λ/2
3. λ/4
4. λ/8

Answer. 2. λ/2

Question 35. When feeble sound is changed to loud sound, we increase its ______.

1. Frequency
2. Speed
3. Amplitude
4. Velocity

Answer. 3. Amplitude

Question 36. The speed of sound in a gas is not affected by the change in

1. Wavelength of wave
2. Amplitude of wave
3. Pressure
4. Speed

Answer.

1. Wavelength of wave
2. Amplitude of wave
3. Pressure

Question 37. The speed of sound in a medium depends on ______.

1. Time
2. Volume
3. Elasticity
4. Density

Answer.

3. Elasticity

4. Density

Question 38. Sound can travel through ______.

1. Solid
2. Liquid
3. Gas
4. Vacuum

Answer. 

1. Solid
2. Liquid
3. Gas

Question 39. Choose the correct statement

1. The time taken for one complete oscillation in the density of the medium is called the time period of the sound wave.
2. The amplitude of sound wave is the height of the crest or tough.
3. With high frequency, sound has high pitch
4. When frequency is low, sound has low pitch

Answer.

1. The time taken for one complete oscillation in the density of the medium is called the time period of the sound wave.
2. The amplitude of sound wave is the height of the crest or tough.
3. With high frequency, sound has high pitch
4. When frequency is low, sound has low pitch

Question 40. Choose the correct statement

1. If amplitude is bigger, sound is soft.
2. If amplitude is smaller, sound is loud.
3. If amplitude is bigger, sound is loud.
4. If amplitude is smaller, sound is soft.

Answer. 

3. If amplitude is bigger, sound is loud.
4. If amplitude is smaller, sound is soft.

Question 41. Light can travel through ______.

1. Solid
2. Liquid
3. Gas
4. Vacuum

Answer. 

1. Solid
2. Liquid
3. Gas
4. Vacuum

Question 42. Choose the correct unit.

1. The S.I. unit of frequency is Hertz.
2. The S.I. unit of wavelength is metre.
3. The S.I. unit of time is hour.
4. The S.I. unit of time is second.

Answer. 

1. The S.I. unit of frequency is Hertz.
2.The S.I. unit of wavelength is metre
4. The S.I. unit of time is second.

Question 43. Choose the incorrect statement

1. The pitch of sound depends on the frequency of vibration.
2. The pitch of sound depends on the amplitude of vibration.
3. The loudness of sound depends upon the amplitude of vibration.
4. The loudness of sound depends upon the frequency of vibration.

Answer. 

2. The pitch of sound depends on the amplitude of vibration.
4. The loudness of sound depends upon the frequency of vibration.

Question 44. Choose the correct statement

1. Speed of sound in Glass at 25 °C is 3980 m/s.
2. Speed of sound in Oxygen at 25 °C is 390 m/s.
3. Speed of sound in Steel at 25 °C is 5960 m/s.
4. Speed of sound in Hydrogen at 25 °C is 1284 m/s.

Answer. 

1. Speed of sound in Glass at 25 °C is 3980 m/s.
3. Speed of sound in Steel at 25 °C is 5960 m/s.
4. Speed of sound in Hydrogen at 25 °C is 1284 m/s.

Question 45. Choose the incorrect speed of sound in air.

1. 344 m/s
2. 355 m/s
3. 366 m/s
4. 377 m/s

Answer. 

2. 355 m/s
3. 366 m/s
4. 377 m/s

Question 46. For hearing an echo, the minimum distance should be:

1. less than 10 m
2. between 10 m and 15 m
3. 17 m or more
4. none of the above

Answer. 3. 17 m or more

Question 47. The quantities that a travelling wave carry with it are

1. mass
2. velocity
3. wavelength
4. energy

Answer. 4. energy

Question 48. Sonar works on the principle of

1. reflection of sound waves
2. momentum of sound waves
3. energy of sound waves
4. refraction of sound waves

Answer. 1. reflection of sound waves

Question 49. When a wave goes from one medium to another medium, which quantity does not changes?

1. frequency
2. wavelength
3. velocity
4. time period

Answer. 1. frequency

Question 50. Hearing of repetition of sound after reflection from a distant object is called:

1. reverberation
2. resonance
3. echo
4. none of these

Answer. 3. echo

Question 51. Which of the following sound waves can not be heard by human?

1. 20 Hz
2. 500 Hz
3. 15 Hz
4. 1500 Hz

Answer. 3. 15 Hz

Question 52. A boy sitting in a boat fires a gun. An observer P is at a distance of 50 m from the boat. Another observer Q is a diver, who is 50 m under water. Both hear the sound of gun:

1. P hears the sound first
2. Q hears the sound first
3. both P and Q hear the sound
4. none of the above

Answer. 2. Q hears the sound first

Question 53. Mechanical waves on the surface of a ­liquid are:

1. transverse
2. longitudinal
3. torsional
4. both transverse and longitudinal (or ripples)

Answer. 4. both transverse and longitudinal (or ripples)

Question 54. Ultrasonic waves are those waves:

1. which a man can hear
2. which a man cannot hear
3. which are of high velocity
4. which have high amplitude

Answer. 2. which a man cannot hear

Question 55. If the amplitude of waves at a distance r from a point source is A, the amplitude at a distance 2r will be:

1. 2A
2. A
3. A/2
4. A/4

Answer. 3. A/2

Question 56. Sound travels in air as:

1. longitudinal waves
2. transverse waves
3. torsional waves
4. electromagnetic waves

Answer. 1. longitudinal waves

Question 57. For the wave shown in figure, the frequency and wavelength, if its speed is 320 m/sec, are

1. 8 cm, 400 Hz
2. 80 cm, 40 Hz
3. 8 cm, 4000 Hz
4. 40 cm, 8000 Hz

Answer. 3. 8 cm, 4000 Hz

Question 58. With the propagation of a longitudinal wave through a material medium, the quantities transmitted in the direction of propagation are

1. energy, momentum and mass
2. energy
3. energy and mass
4. energy and linear momentum

Answer. 4. energy and linear momentum

Question 59. Light can travel in vacuum but no sound, because:

1. speed of sound is very much slower than light
2. light waves are electromagnetic in nature
3. sound waves are electromagnetic in nature
4. light waves are not electromagnetic in nature

Answer. 2. light waves are electromagnetic in nature

Question 60. Sound energy is basically:

1. mechanical energy
2. electromagnetic energy
3. potential energy
4. electrical energy

Answer. 1. mechanical energy

Question 61. The transfer of energy in a material medium due to the periodic motion of its particle is called:

1. wave front
2. wave motion
3. pulse
4. none of these

Answer. 2. wave motion

Question 62. The sound waves in a medium are characterised by the:

1. linear motion of particles in the medium
2. rotatory motion of particles in the medium
3. oscillatory motion of particles in the medium
4. none of the above

Answer. 3. oscillatory motion of particles in the medium

Question 63. The sound waves which travel in the air are called:

1. transverse waves
2. longitudinal waves
3. polarised waves
4. none of the above

Answer. 2. longitudinal waves

Question 64. In case of transverse waves the particles of a medium vibrate:

1. in the direction of wave propagation
2. opposite to the direction of wave propagation
3. at right angles to the direction of wave propagation
4. none of the above

Answer. 3. at right angles to the direction of wave propagation

Question 65. A sonic boom is produced in the air when an aircraft flies at a speed:

1. equal to the speed of sound
2. more than the speed of sound
3. less than the speed of sound
4. climbs vertically

Answer. 2. more than the speed of sound

Question 66. The animal which cannot hear ultrasonic waves is:

1. bat
2. cow
3. dog
4. dolphin

Answer. 2. cow

Question 67. A longitudinal wave consists of:

1. crest and troughs in the medium
2. compressions and rarefactions in the medium
3. both (a) and (b)
4. neither (a), nor (b)

Answer. 2. compressions and rarefactions in the medium

Question 68. The transverse waves can propagate only in:

1. liquids
2. gases
3. solids
4. vacuum

Answer. 3. solids

Question 69. In the compression region of the medium in case of longitudinal wave:

1. the volume momentarily decreases
2. the density momentarily increases
3. the pressure momentarily increases
4. all of the above

Answer. 4. all of the above

Question 70. A part of longitudinal wave in which particles of medium are farther away than the normal particles is called:

1. rarefaction
2. trough
3. compression
4. crest

Answer. 1. rarefaction

Question 71. A slinky can produce in laboratory:

1. transverse waves only
2. longitudinal waves only
3. both (a) and (b)
4. none of the above

Answer. 3. both (a) and (b)

Question 72. In case of transverse wave:

1. the hump on the –y axis is called trough
2. the lowest point the hump on the –y axis is called trough
3. the hump on +y axis is called trough
4. the highest point on the hump on the +y axis is called trough

Answer. 2. the lowest point the hump on the -y axis is called trough

Question 73. The wavelength is the linear distance between the:

1. two consecutive compressions
2. two consecutive rarefactions
3. one compression and one rarefaction
4. both (a) and (b)

Answer. 4. both (a) and (b)

Question 74. The change in density/pressure of a medium from maximum value to minimum value and again to maximum value, due to the propagation of a longitudinal wave is called complete:

1. oscillation
2. frequency
3. amplitude
4. none of these

Answer. 1. oscillation

Question 75. The number of oscillations passing through a point in unit time is called:

1. vibration
2. frequency
3. wavelength
4. none of these

Answer. 2. frequency

Question 76. The bat hunts it prey by emitting and receiving reflected:

1. super sonic waves
2. ultrasonic waves
3. sonic waves
4. infrasonic waves

Answer. 2. ultrasonic waves

Question 77. The SI unit of frequency is

1. hertz
2. gauss
3. decibel
4. none of these

Answer. 1. hertz

Question 78. If the frequency of a wave is 25 Hz, the total number of compression and rarefactions passing through a point in 1 second is

1. 25
2. 50
3. 100
4. none of these

Answer. 2. 50

Question 79. Amplitude of a longitudinal wave in the medium

1. is the extent to which a medium gets compressed
2. is the extent to which a medium gets rarefied
3. is the extent to which a medium gets rarefied
4. none of the above

Answer. 3. is the extent to which a medium gets rarefied

Question 80. The linear distance between a compression and a rarefaction or a crest and a trough is:

1. \(\frac{\lambda}{2}\)
2. \(\frac{\lambda}{4}\)
3. 1
4. \(\frac{3 \lambda}{2}\)

Answer. 1. \(\frac{\lambda}{2}\)

Question 81. A stretched string is plucked gently to produce a note. The string is producing:

1. longitudinal waves
2. stationary waves
3. transverse waves
4. both (a) and (c)

Answer. 3. transverse waves

Question 82. A stretched slinky is given a sharp push along its length. A wave travels from one end to another. The wave so produced is:

1. transverse wave
2. longitudinal wave
3. stationary wave
4. none of these

Answer. 2. longitudinal wave

Question 83. A longitudinal sound wave in air consists:

1. a number of rarefaction pulses one after the other
2. a number of compression pulses one after the other
3. compression and rarefaction pulses alternating with each other
4. a rarefaction pulse followed by compression pulse, separated by some distance

Answer. 3. compression and rarefaction pulses alternating with each other

Question 84. Infrasonic vibrations have frequency:

1. less than 10 Hz
2. less than 20 Hz
3. between 20 and 20,000 Hz
4. more than 20,000 Hz

Answer. 2. less than 20 Hz

Question 85. The range of sonic waves is between:

1. 20 Hz to 2000 Hz
2. 20 Hz to 10,000 Hz
3. 20 Hz to 15,000 Hz
4. 20 Hz to 20,000 Hz

Answer. 4. 20 Hz to 20,000 Hz

Question 86. When a vibrating object moves backwards, it creates a region of low pressure called ______.

1. Reflection
2. Rarefaction
3. Wavelength
4. Frequency

Answer. 2. Rarefaction

Question 87. The distance travelled by a wave in one second is called its ______.

1. Wave velocity
2. amplitude
3. Wavelength
4. Frequency

Answer. 1. Wave velocity

Question 88. The unit of wave velocity is ______.

1. m
2. s
3. m/s
4. km

Answer. 3. m/s

Question 89. Choose the correct equation

1. Wavelength = wave velocity/time period
2. Wavelength = wave velocity × time period
3. Wave velocity = wavelength × time period
4. Wavelength = wave velocity

Answer. 2. Wavelength = wave velocity/time period

Question 90. Sound cannot travel in ______.

1. Solid
2. Liquid
3. Gas
4. Vacuum

Answer. 4. Vacuum

Question 91. ______ is an instrument used by doctors for listening breaths.

1.  Radar
2. Stethoscope
3. Soundboard
4. Loudspeaker

Answer. 2. Stethoscope

Question 92. Soundboard works on the basis of law of ______ of sound waves.

1. Reflection
2. Rarefaction
3. Newton
4. None of the above

Answer. 1. Reflection

Question 93. The sound that comes to our ear after reflection is called ______.

1. Reflection
2. Infrared
3. Ultrasound
4. Echo

Answer. 4. Echo

Question 94. The speed of sound in a gas is not affected by the change in ______.

1. Distance
2. Time
3. Pressure
4. Speed

Answer. 3. Pressure

Question 95. The speed of sound in a gas increases with the increase in the ______ of gas.

1. Speed
2. Density
3. Temperature
4. None of the above

Answer. 3. Temperature

Question 96. ______ is used to detect and find the distance of objects under water.

1. Ultrasonography
2. Sonar
3. Radiology
4. Chronology

Answer. 2. Sonar

Question 97. The energy carried by ultrasound is very ______.

1. High
2. Low
3. Medium
4. None of the above

Answer. 1. High

Question 98. The frequency range of hearing for human is ______.

1. 20 Hz – 20 kHz
2. 30 Hz – 30 kHz
3. 40 Hz – 40 kHz
4. 50 Hz – 50 kHz

Answer. 1. 20 Hz – 20 kHz

Question 99. The sound of frequency less than 20 Hz is known as ______.

1. Ultrasound
2. Infrasonic
3. Rarefaction
4. Reflection

Answer. 2. Infrasonic

Question 100. The sound of frequency greater than 20 kHz is known as ______.

1. Ultrasound
2. Infrasonic
3. Rarefaction
4. Reflection

Answer. 1. Ultrasound

Chapter 5 Sound Short Answer Type Question And Answers

Question 1. If an echo is heard 5 seconds later in a theatre, calculate the distance of the reflecting surface.
Answer.

Given:

If an echo is heard 5 seconds later in a theatre

Total distance travelled by sound wave,

D = 5 × 340 = 1700 m

Distance of the reflecting surface

= D/2 = 1700/2 = 850 m

Distance of the reflecting surface = 850 m

Question 2. Distinguish between intensity and loudness.
Answer.

Difference between intensity and loudness:

Question 3. What are the requirements of the medium for the sound to propagate?
Answer.

Requirements of the medium for the sound to propagate:

The medium required for propagation of sound must have the following properties:

The medium must be elastic so that its particles may come back to their initial positions after displacement on either side.

The medium must have inertia so that its particles may store mechanical energy.

The medium should be frictionless so that there is no loss of energy in propagation of sound through it.

Read And Learn More NEET Foundation Short Answer Questions

Question 4. A tuning fork having a frequency of 250 Hz is made to vibrate by striking it against a rubber pod. What is the wavelength of the sound waves it produces in

1. air  
2. water
3. iron?

Velocity of sound in air, water and iron = 330 ms^-1, 1500 ms^-1 and 5 kms^-1 respectively.
Answer.

Given

A tuning fork having a frequency of 250 Hz is made to vibrate by striking it against a rubber pod.

Velocity of sound in air, water and iron = 330 ms^-1, 1500 ms^-1 and 5 kms^-1 respectively.

We know that

v = fλ

i.e., λ = \(\frac{v}{f}\)

In air, \(\lambda_a=\frac{330 \mathrm{~ms}^{-1}}{250 \mathrm{~s}^{-1}}\)

= 1.32m

Similarly,

\(\lambda_w=\frac{1500 \mathrm{~ms}^{-1}}{250 \mathrm{~s}^{-1}}\)

= 6.0m

In iron,

\(\lambda_{\text {iron }}=\frac{5000 \mathrm{~ms}^{-1}}{250 \mathrm{~s}^{-1}}\)

= 20.0 m

Question 5. If a tuning fork having a frequency of 400 Hz is made to vibrate continuously how many

1. Compression
2. Rarefactions

Pass a point P in air in 0.1 s?
Answer.

Given

A tuning fork having a frequency of 400 Hz is made to vibrate continuously

When a tuning fork vibrates once, it produces one sound wave, which consists of one compression and one rarefaction.

∴ Its frequency is 400 Hz, it vibrates 400 times in one second.

In one second, it vibrates 400 times.

So, in 0.1 seconds it vibrates 0.1 × 400 = 40 times.

So, it will produce 40 waves, i.e., 40 compressions and 40 rarefactions.

∴ Number of compressions passing a point P  in 0.1 second is 40.

Similarly, a number of rarefaction passing a point P is 0.1 second is also 40.

Question 6. Displacement–The distance graph of particles vibrating in a gas under the influence of a tuning fork of frequency 512 Hz is as follows: Find the velocity of sound in the gas.

Answer.

Given

Points A and B represent the consecutive compressions. Distance between them is called ‘wavelength’ (λ).

So, λ = (100 cm − 20 cm) = 80 cm

Distance between points C and D = (120 cm − 40 cm) = 80 cm is also the wavelength(λ).

∴ λ = 80 cm = 0.8 m

We know that

v = fλ

= 512 × 0.8

= 409.6 ms^-1

∴ Velocity of sound in the gas = 409.6 ms^-1

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Question 7. A train is travelling in a railway track made of iron. A boy standing far away puts his ears to the track. He hears two sounds. Why? Calculate the time interval between these two sound waves.
Velocity of sound in air = v_a
Velocity of sound in iron = v_s (where v_s > v_a)
Answer.

Given

A train is travelling in a railway track made of iron. A boy standing far away puts his ears to the track. He hears two sounds.

It is because he receives the sound waves travelling through air as well as through iron. Since sound travels much faster through iron he will the hear sound travelling through iron first.

Time ‘t1’ taken by the sound to travel from the train to the boy through the iron rail is given by

\(\text { Time }=\frac{\text { Distance }}{\text { Speed }}\)

\(t_1=\frac{d}{v_n}\)  (1)

Similarly, time ‘t2’ taken by sound to travel to him is,

\(t_2=\frac{d}{D_d}\)  (2)

∴ Time interval ∆t between two sound waves reaching the boy is

∆t = t₂ − t₁

= \(\left(\frac{d}{v_a}-\frac{d}{v_n}\right)\)

Question 8. Calculate the velocity of sound through iron given that the modulus of elasticity for iron = 2 × 10¹¹ Pa and density of iron = 8 × 10³ kgm^-3.
Answer.

Velocity of sound through a solid is given by

\(v=\sqrt{\frac{Y}{\rho}}\)

Where Y = young’s modulus

ρ = Density

V = \(\sqrt{\frac{\left(2 \times 10^{11}\right) \mathrm{Pa}}{\left(8 \times 10^3\right) \mathrm{kgm}^{-3}}}\)

= \(\sqrt{0.25 \times 10^8 \frac{\mathrm{Nm}^{-2}}{\mathrm{kgm}^{-3}}}\)

= \(\sqrt{25 \times 10^6 \frac{\mathrm{kgms}^{-2} \mathrm{~m}^{-2}}{\mathrm{kgm}^{-3}}}\)

= \(\sqrt{25 \times 10^6 \mathrm{~m}^2 \mathrm{~s}^{-2}}\)

= 5 x 10³ ms^-1

The velocity of sound = 5 x 10³ ms^-1

Question 9. How does a SONAR work?
Answer:

Working Of SONAR

SONAR is a device which is used in the ships to locate rocks, icebergs submarines, old sank in the seas etc. Ultrasonic sound of high frequency are sent from a ship on the surface. The waves travel in the straight line till they hit something like shipwreck or submarine.

On hitting the body these waves are reflected. The transmitter sending the waves note the time lag between sending the signal and receiving it back. This time lag is multiplied by speed of sound in water and the distance calculated is halved to get the actual distance of the object from the ship.

Question 10. Describe the structure and function of a human ear.
Answer:

Structure and function of a human ear:

The human ear consists of three parts:

1. Outer ear: It is functionally the simplest part of the ear. It consists of ‘pinna’ or auricle i.e. the visible portion of the ear, the external acoustic meatus i.e. the outside opening to the ear canal and the ear canal.
2. Middle ear: The middle ear consists of eardrum or tympanic membrane connected at the end of auditory canal. The eardrum vibrates when compression and rarefaction of the sound waves hit it. The three bones (hammer, anvil and stirrup) present in the middle ear the pressure variations several times. Thus the middle ear transmits the sound wave’s amplified pressure variation to the inner ear.
3. Inner ear: The inner ear converts the sound waves amplified pressure variation into electrical signals. This work is done by cochlea, a snail-shaped organ. The cochlea is filled with water like fluid and its inner surface has large number of hair like nerve cells. The amplified pressure variation produces vibrations in the nerve cells and they in turn release electrical signals which are sent to the brain along the auditory nerve. The brain interprets the electrical signals through a complex process as sounds.

Question 11. What are the factors affecting the speed of sound in a gas?
Answer:

Speed of sound in a gas is affected by:

1. Density
2. Temperature
3. Humidity
4. Direction of wind

Question 12. What are the factors which does not affect the speed of sound in air?
Answer:

The factors which does not affect the speed of sound in air are:

1. Wavelength
2. Frequency
3. Amplitude
4. Pressure

Question 13. What are the laws of reflection of sound?
Answer:

The laws of reflection of sound are:

• The angle of incidence is equal to angle of reflection.
• The incident ray, reflected ray and normal at the point of incidence, all lie in the same plane.

Question 14. What do you mean by reverberation?
Answer:

Reverberation:

When echo is heard multiple times, due to repeated and multiple reflections of sound from different reflecting surfaces, it causes persistence of sound. This phenomenon is called reverberation.

Question 15. Name the devices which use multiple reflections of sound.
Answer:

Loudspeaker, megaphone, soundboard and stethoscope are the devices which use multiple reflections of sound.

Question 16. A boy shouted at the top of the mountain. The echo is heard after 10 seconds. Speed of the sound is 450 m/s. How far is the mountain from the boy?
Answer:

Given

A boy shouted at the top of the mountain. The echo is heard after 10 seconds. Speed of the sound is 450 m/s.

v = 450 m/s

T = 10 s

Distance d = 450 × 10 = 4500 m

As sound has to travel twice the distance, hence distance between boy and mountain = 4500/2

= 2250 m

Hence distance between boy and mountain = 2250 m

Question 17. Why sound is called a mechanical wave?
Answer:

Mechanical wave:

Sound is called a mechanical wave because it requires a medium to travel from one place to another.

Question 18. What properties should the medium have for the propagation of sound?
Answer:

The medium required for propagation of sound must have the following properties:

• The medium should be elastic so that its particles comes back to the mean position after displacement on the either side.
• The medium must have inertia so that its particles may store mechanical energy.
• The medium should be frictionless so that there is no loss of energy in propagation of sound through it.

Question 19. What do you mean by crest and trough?
Answer:

Crest And Trough:

The position of maximum upward displacement is called crest and position of maximum downward displacement is called trough. These two are created in the medium during the propagation of transverse wave.

Question 20. What is the difference between progressive wave and stationary wave?
Answer:

The difference between progressive wave and stationary wave

Progressive waves start at a point and moves indefinitely and infinitely to all parts of the medium. These waves transmit energy from one place to another. While standing waves appear to stand at a place and confined between two points in a medium. These waves store energy in them.

Question 21. What are the characteristics of a sound wave?
Answer:

The characteristics of the sound waves are:

• Amplitude
• Time period
• Frequency
• Wavelength
• Wave velocity

Question 22. On which factors does the speed of a sound in a medium depends?
Answer:

Speed of sound in a medium depends on elasticity of the medium as well as density of the medium.

Question 23. A sound wave has a frequency of 200 Hz. Wavelength is 15 m. How much time it will take to cover 2 km?
Answer:

Given

A sound wave has a frequency of 200 Hz. Wavelength is 15 m.

ν = 200 Hz

λ = 15 m

Speed v = ν × λ = 200 × 15 = 3000 m/s

Time t = d/υ

= 2000/3000

= 0.67 seconds

0.67 seconds time will it take to cover 2 km

Question 24. A sound has a frequency of 220 Hz. Its speed is 440 m/s. What will be the wavelength of the sound wave?
Answer:

Given

A sound has a frequency of 220 Hz. Its speed is 440 m/s.

ν = 220 Hz

v = 440 m/s

λ = v/ν = 440/220 = 2 m

The wavelength of the sound wave λ = 2 m

Chapter 5 Sound Long Answer Type Question And Answers

Question 1. Differentiate between transverse and longitudinal waves.
Answer.

Difference between transverse and longitudinal waves:

Question 2. Explain how defects in a metal block can be detected using ultrasound.
Answer.

Defects in a metal block can be detected using ultrasound:

Ultrasounds are used to detect cracks in the metal blocks. The cracks inside the metal blocks, which are imperceptible from outside, decreases the strength of the structure.

Ultrasonic waves can pass through the metal block and detectors are conditioned to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected indicating the occurrence of the flaw or defect in that metal block.

Read and Learn More NEET Foundation Long Answer Questions

Question 3. Calculate the difference in Newton’s value of velocity of sound in air and that found by Pascal.
Answer.

The difference in Newton’s value of velocity of sound in air and that found by Pascal:

Velocity of sound in a gas is given by

v = \(\sqrt{\frac{E}{\rho}}\)

Where E is the modulus of elasticity of the gas.

Newton said ‘when sound travels through air through compression and rarefactions, the changes taking place in air are isothermal changes.’ For isothermal changes,

E = Pressure of gas

= Pressure of air

= 1.013 × 10⁵ Nm^-2

∴ According to Newton,

v_a = \(\sqrt{\frac{P_a}{\rho_a}}\)

v_a = \(\sqrt{\frac{1.013 \times 10^5 \mathrm{Nm}^{-2}}{1.29 \mathrm{kgm}^{-3}}}\)

Newton’s value of v_a = 280 ms^-1

Almost a century later, Laplace said ‘Sound travels very rapidly through air such rapid changes cannot be isothermal. They must be adiabatic in nature.’

For adiabatic changes,

E = YP

= 1.4 × 1.013 × 10⁵ Pa

So, according to Pascal,

va = \(\sqrt{\frac{Y P_a}{\rho_e}}\)

= \(\sqrt{\frac{1.4 \times 1.013 \times 10^5}{1.29}}\)

= 331.6 ms^-1

Velocity of sound in air at 0 °C is about 332 ms^-1.

So, Laplace’s value is very close to the actual value of velocity of sound in air. Thus Laplace corrected Newton. This is therefore, called

Laplace’s correction.

∆v = (331.6 − 280)ms^-1.

= 51.6 ms^-1.

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Question 4. At what temperature the velocity of sound in air, will be double that of air at 0 °C ? (Given v0 = 332 ms^-1).
Answer.

We know that,

\(\frac{v_2}{v_1}=\sqrt{\frac{T_2}{T_1}}\) \(\frac{v_2}{v_0}=\sqrt{\frac{T_2}{T_1}}\)

\(\frac{2 v_0}{v_0}=\sqrt{\frac{T_2}{273}}\)   (∴ V₂ = 2V₀)

Squarring on both sides, we get

\(4=\frac{T_2}{273}\)

T₂ = 1092 K

= (1092 − 273) °C

= 819 °C

At 819 °C temperature the velocity of sound in air, will be double that of air at 0 °C

Question 5. Velocity of sound in a gas at STP is 400 ms^-1. If both the pressure and the absolute temperature of the gas are doubled, then how will the velocity of sound change?
Answer.

Given:

Velocity of sound in a gas at STP is 400 ms^-1. If both the pressure and the absolute temperature of the gas are doubled

Change in pressure has no effect on the velocity of sound. Only temperature change has,

Given: T₁ = 0 °C = 273 K, v₁ = 400 ms^-1, T₂ = 2 × 273 k,

We know that, T₂ = ?

\(\frac{v_2}{v_1}=\sqrt{\frac{T_2}{T_1}}\)

\frac{v_2}{400}=\sqrt{\frac{(2 \times 273)}{273}}

v₂ = 400 \sqrt{2}

= 565.7 ms^-1.

The Change In Velocity Of Sound Is 565.7 ms^-1.

Question 6. A boy blows a whistle and its echo from a distant wall is heard after 1.8 seconds. How far is the wall from him? Velocity of sound in air at room temperature = 340 ms^-1.
Answer.

Given:

A boy blows a whistle and its echo from a distant wall is heard after 1.8 seconds.

If d be the distance of the wall from the boy, then sound travels a distance d to the wall and back to the boy.

So, total distance travelled by sound is 2d.

Time taken by sound to go to the wall(reflection of sound) and back.

\(t=\frac{\text { Distance }}{\text { Velocity }}\) \(t=\frac{2 d}{v}\)

=> \(1.6=\frac{2 d}{340}\)

2d = 340 x 1.6

∴ \(d=\frac{340 \times 1.6}{2}\)

= 272 m

Question 7. Two ships are 6 km apart in Indian Ocean. Signal sent by one ship is reflected by the ocean bed and received at the second ship after 6.6 s. Find the depth of the Indian Ocean. (Velocity of sound in water = 1500 ms^-1)
Answer.

Given:

Two ships are 6 km apart in Indian Ocean. Signal sent by one ship is reflected by the ocean bed and received at the second ship after 6.6 s.

The figure below shows two ships S₁ and S₂. Signal sent by ships S₁ travels to the ocean bed along S1B and gets reflected along BS₂ to reach the ship S₂. So, distance travelled by sound is S₁BS₂ = 2 S₁B.

In ∆ S₁BM,

\(S_1 B=\sqrt{d^2+\left(S_1 M\right)^2}\)

Time taken by (sound) signal to travel distance x = S₁BS₂ is given by

\(t=\frac{\text { Distance }}{\text { Velocity }}=\frac{S_1 B S_2}{v}\)

= \(\frac{S_1 B+B S_2}{v}\)

= \(\frac{2 S_1 B}{v}\)   (∴ Bs₂ = s₁B)

\(t=\frac{2 \sqrt{d^2+\left(S_1 M\right)^2}}{v}\)

∴ \(\sqrt{d^2+\left(S_1 M\right)^2}=\left(\frac{v t}{2}\right)\)

Squarring on both sides,

\(d^2+(S, M)^2=\left(\frac{v t}{2}\right)^2\) \(d^2+(3000)^2=\left(\frac{1500 \times 6.6}{2}\right)^2\)

d² + (3000)² = (4950)²

∴ d² = 4950² − 3000²

= (4950 + 3000)(4950 − 3000)

d2 = (7950)(1950)

\(d=\sqrt{(7950) \times(1950)}\)

⇒ d = 3937.4 m

⇒ d ≅ 3940 m

⇒ d ≅ 3.94 km

The depth of the Indian Ocean ≅ 3.94 km

Question 8. A sound wave of wavelength 0.332 m has a time period of 10^-3 s. If the time period is decreased to 10^-4 s. Calculate the wavelength and frequency of the new wave. Name the subjective property of sound related to its frequency and the light related to its wavelength.
Answer.

Given:

A sound wave of wavelength 0.332 m has a time period of 10^-3 s. If the time period is decreased to 10^-4 s.

Here λ = 0.332 m

Time taken to travel,

t = 10^-3 s

Velocity = \(\frac{\lambda}{t}\)

v = \(\frac{0.33}{10^{-3}}\)

v = 0.33 × 10³

v = 330 m/s

Time period for second wave = 10^-4 s

Wavelength λ = vT

= 330 × 10^-4

Wavelength λ = 0.033 m

Frequency = \(\frac{1}{T}\)

= \(\frac{1}{10^{-3}}\)

Frequency = 10³ Hz

Question 9. Derive a relation between Wave-Velocity, frequency and wavelength.
Answer.

A relation between Wave-Velocity, frequency and wavelength:

Let velocity of wave = v

Time period = T

Frequency = υ

Wavelength = λ

As per the definition of wavelength,

λ = Distance travelled by wave in one time period

= Wave Velocity × Time period

= v × T

vT = λ

t = \(\frac{1}{v}\)

\(v \times\left(\frac{1}{v}\right)=\lambda\)

Therefore, v = λυ.

Hence,

Wave Velocity = Frequency × Wavelength

Question 10. Meera is standing between two hills. She shouted loudly and hears first echo after 0.5 sec and second echo after 1 sec. What is the distance between two hills?
Answer.

Given:

Meera is standing between two hills. She shouted loudly and hears first echo after 0.5 sec and second echo after 1 sec.

Let the distance between nearest cliff and

Meera = x m and the distance between distant cliff and Meera = y m

Distance between two cliff = (x + y) m

Total distance covered by sound to produce first echo = 2x m and time = 0.5 sec.

2x = 340 × 0.5

\(x=340 \times \frac{0.5}{2}=85 \mathrm{~m}\)

Total distance covered by sound to produce second echo = 2y m and time = 1 sec

2y = 340 × 1

y = \(340 \times \frac{1}{2}\)

y = 170m

So distance between the two cliffs = (85 + 170) = 255 m

Question 11. A man fires a gun and hears its echo after 5 seconds. The man then moves 310 m towards the hill and fires his gun again. This time he hears the echo after 3 seconds. Calculate the speed of sound.
Answer.

Given:

A man fires a gun and hears its echo after 5 seconds. The man then moves 310 m towards the hill and fires his gun again. This time he hears the echo after 3 seconds.

Let d be the distance between the man and the hill in the beginning

v = \(\frac{2 d}{t}\)

v = \(\frac{2 d}{5}\)   (1)

He moves 310 m towards the hill. Therefore distance will be (d − 310) m.

v = \(2 \frac{(d-310)}{3}\)   (2)

Since velocity of sound is same, equating (1) and (2).

\(\frac{2 d}{5}=2 \frac{(d-310)}{3}\)

3d = 5d − 1550

2d = 1550

d = 775 m

Velocity of sound v = \(2 \times \frac{775}{5}\)

Velocity of sound v = 310 ms^-1

Question 12. An engine is approaching a hill at a constant speed. When it is at a distance 0.9 km, it blows whistles, whose echo is heard by the driver after 5 s. If the speed of sound is 340 ms^-1,calculate the speed of the engine.
Answer.

Given:

An engine is approaching a hill at a constant speed. When it is at a distance 0.9 km, it blows whistles, whose echo is heard by the driver after 5 s.

Let v_e be the speed of the engine.

Distance covered by the engine in 5 s = 5 v_e

Distance covered by sound in reaching the hill and coming back to moving driver

= 900 × 2 − 5v_e

= 1800 − 5v_e

According to given condition,

t = \(\frac{\left(1800-5 v_e\right)}{v}\)

As t = 5 s and v (speed of sound) = 340 ms^-1

5 = \(\frac{(1800-5 v)}{340}\)

1700 = 1800 − 5v_e

Or v_e = 20 ms^-1

Physics Chapter 4 Work And Energy

In previous chapter we have discussed about fundamental concepts of physics, which deal with the laws of nature like motion, forces, and Newtons laws of motion and gravitation, etc. Work and energy are the other two basic principles of nature which we come across knowingly or unknowingly in our day to day life.

In this chapter, we will discuss about some of the basic concepts on which work and energy are co-related. Also, energy and power are closely related to work.

All living beings need food to survive. Complex food molecules are broken down by our body and converted into simple soluble form, which in turn is absorbed by the body to get ‘Energy’. Thus, energy can be defined as the element which allows us to perform any function.

For our day to day activities like singing, dancing, running, etc., we need energy. Without energy we cannot perform any work.

For machines, cars, etc., the energy is provided by electricity or the fuel which we provide. Thus, any object whether living or non-living requires energy to do any work.

Chapter 4 Work And Energy

Work

In the language of science, work is said to be done only if the force applied in a specific direction produces motion in the body. In other words, if the body displaces from its original position, work is said to be done otherwise it is not done irrespective of all your efforts. In our everyday life, we consider any useful mental or physical labour as work.

Certain activities like playing in a field, chit chatting with friends, singing a song, watching television, attending a party are sometimes not counted as work. What defines ‘work’ depends on how we use it in science.

From the above mentioned examples, it is clear that how work we usually do is different from the scientific definition of work. To understand the concept better, we would study the concept of work done by a constant force.

We will consider a constant force ’F’ acting on the body and body being displaced in the direction of the force by a distance ’S’ as shown.

Let ’W’ be the work done.

According to the definition,

Work done = force × displacement

Mathematically,

W = F × S

Elaborating the above equation, the work done by a body is equal to the magnitude of the force applied on the body multiplied by the displacement carried in the direction of force. Work has only magnitude and no direction. If either force or displacement in the above equation is zero then the work becomes zero.

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If in the above equation, 1 newton of force is applied on the body producing a ­displacement of 1 metre in the body in the direction of motion, then the work done is said to be 1 Nm or 1 Joule. (1 Nm = 1 Joule).

If force F acts in the direction of displacement at an angle θ, then in the direction of displacement the rectangular component will be represented by F cos θ.

Work done = Force(rectangular component) × displacement

W = F cos θ × S

Therefore, depending on the value of θ (i.e., cos θ) work done can be positive, negative or zero.

Concept of Positive and Negative Work

Work can be positive or negative depending upon the direction of force applied. If the force applied is along the direction of the displacement, work done is positive. Example of such situation is pulling of a toy by a kid (parallel to the ground), pushing the door, etc. In these examples, work done is equal to the product of force and displacement.

On the other hand, when the force applied and displacement act in the opposite directions, the work done is said to be negative. Example of this type of work is, when a body is moving with a uniform velocity and suddenly a retarding force is exerted on the body to halt its motion.

The retarding force is opposite to the direction of motion. The angle between the force applied and the displacement is 180°. The work done in this case is said to be negative. Work done is represented by F × (–S) or (–F) × S. Negative work done is indicated by the minus sign.

 

Chapter 4 Work And Energy Track Your Learning Question And Answers

Question 1. The angle between the force & displacement is_________ in case of negative work.

1. 45°
2. 90°
3. 0°
4. 180°

Answer. 3. 0°

Question 2. Which of the above quantity does not depend upon work done on an object?

1. displacement
2. angle between force and displacement
3. force applied
4. initial velocity of the object

Answer. 4. initial velocity of the object

Question 3. If the force applied is along the direction of the displacement, work done is said to be ______.

1. Negative
2. Positive
3. Neutral
4. Cannot be determined

Answer. 2. Positive

Question 4. Nm is a SI unit of

1. Work
2. Power
3. Acceleration
4. Force

Answer. 1. Work

Question 5. kWh is the unit of

1. Work
2. Power
3. Acceleration
4. energy

Answer. 4. energy

Chapter 4 Work And Energy

Every process on this earth requires energy. Our earth has evolved because of energy. The life processes that keep us alive require energy. Every single process needs energy. Just like work, let us understand what energy is, from where do we get energy in the language of science.

In simple language, energy is defined as the capacity of doing work. It is the property possessed by objects which allows them to do work or can exert force on another object. Which means energy is transferred from one object to the other.

The latter may move in the direction of force experienced and hence receives the energy and therefore do some work. Thus, the first object has a capacity to do work. This means that any object that can do work, possesses energy.

Commercial Unit of Energy

When we have to express large quantities of energy, joule is not used. We use a bigger unit of energy called kilowatt hour (kWh). Let us understand with the help of an example, suppose we have a machine that uses 1000  J of energy every second. If this machine is used continuously for one hour, it will consume 1 kWh of energy. Thus, 1 kWh is the energy used in one hour at the rate of 1000 J s^-1 (or 1 kW).

1 kW h = 1 kW × 1 h

1000 W × 3600 s = 3600000 J

1 kW h = 3.6 × 10⁶ J

The energy used in households, industries and commercial establishments is usually expressed in kilowatthour. For example, electrical energy used during a month is expressed in terms of ‘units’. Here, 1 ‘unit’ means 1 kilowatt hour.

Classification of Resources

Natural resources are valuable and easily available to us. They are classified on the basis of their ability to replenish or recover. They are broadly classified into:

1. Renewable resources
2. Non Renewable resources

1. Renewable resources: When the energy source used is easily replenished in a short period and there are practically limitless reserves (inexhaustible). An example is the solar energy that is the source of energy from the sun, or the wind used as an energy resource. Other renewable energies are original solar, natural wind (atmospheric flows), natural ­geothermal, oceanic tidal, natural waterfall (hydraulic flows), etc.
2. Non Renewable resources: They are limited sources of energy on earth (exhaustible) in quantity and therefore are ­non-replenishable. The non-renewable energy sources include, ­non-exclusively, fossil source like petroleum, natural gas, coal, etc.

Different Sources of Energy

There are various sources of energy that are used across the world by human beings to generate power and do the work. Over the years, there are other sources being discovered however, none of them has reached the stage where they can fulfill the power requirements of the modern era.

Human beings rely majorly on natural resources, unfortunately some of them are combustible. For this reason, we should look for artificial and alternate sources.

The reason why we are looking for alternate sources of energy is to produce electricity and run machines on a massive scale.

Solar Energy

Solar energy is the chief source of energy generated from the sun in the form of electric or thermal energy. Solar energy is captured in large solar panels made up of silicon and arsenic which convert the sun’s rays into usable electricity. Besides generating electricity, solar energy is also used in thermal applications.

Wind Energy

In wind energy, wind is used to generate electricity with the help of kinetic energy created by moving air. Wind energy is transformed into electrical energy with the help of wind turbines or wind energy conversion systems. The kinetic energy is then changed to rotational energy, by moving a shaft which is further connected to a ­generator which later produces electrical energy.

Geothermal Energy

Geo means ‘earth’ and thermal means ‘energy’;It is the produced from within the earth. Geothermal energy can be used for heating and cooling purposes or to generate clean electricity. However, for the generation of electricity, high or medium temperature resources are required.

Hydrogen Energy

Hydrogen has the ability to power fuel cells in zero-emission electric vehicles and the fuel cell’s potential for high efficiency. Hydrogen is a tremendous source of energy and can be used as a source of fuel to power ships, vehicles, homes, industries and rockets. It is renewable source of energy. It is environment friendly.

Tidal Energy

Tidal energy converts the energy obtained from tides into other forms of energy mainly electricity. Although because of its complications, it is not yet widely used. Tidal energy has potential for future electricity generation. Tidal power is a eco-friendly energy source.

Hydroelectric Energy

Hydroelectric energy involves water flowing through a pipe before pushing against and turning turbine blades connected to an electric generator. Hydropower provides 16 percent of the world’s electricity.

Biomass Energy

Biomass energy is produced from organic material and is commonly used throughout the world. Chlorophyll present in plants captures the sun’s energy by converting ­carbon dioxide present in the air and water from the ground into carbohydrates through the process of photosynthesis. When the plants are burned, the water and carbon dioxide is again released back into the atmosphere.

Biomass energy is used for heating and cooking in homes and also as a fuel in industrial production. This type of energy produces large amount of carbon dioxide into the atmosphere which is a greenhouse gas, thus it is not very efficient.

Nuclear Power

It is the most novel way of getting energy and quantitatively the most important renewable source of energy. Nuclear energy originates from the fission or fusion of uranium atoms. This produces massive heat to generate steam, which is then used by a turbine generator to generate electricity. Since, nuclear power plants do not burn fuel, they are environment friendly.

Fossil Fuels (Coal, Oil and Natural Gas)

Fossil fuels are the world’s dominant source of energy. Oil is converted into many products, the most used of which is gasoline. Natural gas is starting to become more common, vehicles are seen running on it. To get to the fossil fuel and convert it to use there has to be a heavy destruction and pollution of the ­environment.

The fossil fuel reserves are also limited, expecting to last only another 100 years given are the basic rate of consumption. It is estimated by 2040 that maximum of the fossil fuel deposits would get exhausted.

Understanding Energy Better

We come across different forms of energy in our daily lives. The biggest source of energy is the sun and also the tiniest source comes from nuclei of the atoms. Every action that we do involves energy from hitting a cricket ball, cycling, hitting a nail with the hammer, etc. The body which does work loses energy and the one on which work is done gains energy.

The demand for energy is increasing day by day and the pressure of extracting energy possesses a threat to our planet. We will discuss about energy demands and other threats later in the chapter.

A body which has energy has the capability of doing work. A body which has energy can exert a force on other bodies. Due to this, energy is transferred from one body to the other. The body which received energy may move/does work. The units of work are same as that of energy (Joule). Thus, 1 joule of energy is required to do 1 J of work.

Forms of Energy

The energy present around us is available in different forms like heat energy, sound energy, light energy, electricity, chemical, mechanical (kinetic + potential), etc. They can be interchanged from one form to another. When work done on an object is known, upon which energy is acquired then it is called mechanical energy. They are of two types:

Forms of energy

Kinetic Energy

The energy possessed by a body by virtue of its motion is called as kinetic energy. A body moving can do more work than a stable one. A rotating wheel, moving windmill, bullet fired from a gun, speeding car, etc. Greater the speed of the object, greater is the kinetic energy. Thus, objects in motion possess energy called as kinetic energy.

Now, student may ask how much energy (kinetic) does a moving body possess? We will try to devise a ­formula for that.

Consider the above figure:

Consider a body of mass ’m’ starts moving from rest, with uniform velocity ’u’. After a time interval ’t’ its velocity becomes v.

If initial velocity of the body is u or vi = 0, final velocity vf = v and the displacement of body is ’S’. Then

First of all we will find the acceleration of body.

Using the equation of motion

2aS = v_f² – v_i²

Putting the above mentioned values

2aS = v² – 0

a = \(\frac{v^2}{2 S}\)

Now force is given by

F = ma

Putting the value of acceleration

F = \(m\left(\frac{v^2}{2 S}\right)\)

As we know that

Work done = F⋅S

Putting the value of F

Work done = \(\left(\frac{m v^2}{2 S}\right)(S)\)

Work done = \(\frac{m v^2}{2}\)

or

Work done = \(\frac{1}{2} m V^2\)

Since the work done in motion is called ‘kinetic energy’

i.e. K.E. = Work done

or

K.E. = \(\frac{1}{2} m V^2\)

Potential Energy

The energy possessed by the body by virtue of its height or position is called as potential energy. The energy gets stored in the body because of the work done on the object. The energy while doing work is stored in the body as potential energy.

It does not cause any alterations in its speed or velocity. Some of the examples where we come across with potential energy are that of pulling of rubber band, winding the key of a toy car, water in the water tank at the top of the house, etc.

Potential Energy in a Body at Some Height

An object has energy known as potential energy when raised at a certain height. Greater the potential energy, greater is the height. Work is done on the object, against the gravity in bringing an object to a height. The energy gets stored in the object.

Gravitational potential energy of an object above the ground at a certain point is defined as raising the body to that point against the gravity.

Let us try to devise a formula to calculate the potential energy.

Consider an object of mass, m. Let it be raised through a height h from the ground. A force is required to do this. The minimum force required to raise the object is equal to the weight of the object mg. The object gains energy equal to the work done on it. Let the work done on the object against gravity be W. That is, work done,

W = force × displacement

= mg × h

= mgh

Since work done on the object is equal to mgh, energy equal to mgh units is gained by the object. This is the potential energy (EP) of the object.

E_p = mgh

The potential energy of an object at a height depends on the ground level or the zero level. An object in a given position can have a certain potential energy with respect to one level and a different value of potential energy with respect to another level. At ground potential energy is zero and at some height it is equal to mgh.

The potential attained by the body is independent of the path followed. The potential energy depends only on the initial and final positions. Energy is independent of the path followed.

Conservative and Non-Conservative Forces

Work done by gravity in moving object from one place to another depends only on the initial and final positions and doesn’t depend on the path taken. The work done by gravity from A to B is same by path 1, 2 and 3.

Hence the work done by such forces depends only on initial and final position and not on the path taken. Hence such forces are called conservative forces. Examples of conservative forces are Gravitational forces, spring force, etc.

On the other hand non conservative forces are those in which work done depends on path taken. For example fiction force is non conservative force.

Law of Conservation of Energy

This law states that energy can neither be created nor destroyed. It can only be changed from one form to the other. The total energy of the system remains constant.

According to the law of conservation of energy, energy can only be converted from one form to another; it can neither be created nor destroyed. The total energy before and after the transformation remains the same.

The law of conservation of energy is valid in all situations and for all kinds of transformations.

Consider a simple example. Let an object of mass m be made to fall freely from a height h. At the start, the potential energy is mgh and kinetic energy is zero. Why is the kinetic energy zero? It is zero because its velocity is zero. The total energy of the object is thus mgh.

As it falls, its potential energy will change into kinetic energy. If v is the velocity of the object at a given instant, the kinetic energy would be \(\frac{1}{2} m V^2\). As the fall of the object continues, the potential energy would decrease while the kinetic energy would increase.

When the object is about to reach the ground, h = 0 and v will be the highest. Therefore, the kinetic energy would be the largest and potential energy will be the least. However, the sum of the potential energy and kinetic energy of the object would be the same at all points. That is,

Potential energy + kinetic energy = constant

\(m g h+\frac{1}{2} m v^2=\mathrm{constant}\)

The sum of kinetic and potential energies gives the total mechanical energy of the system.

Efficient use of Energy

Energy is very important to us. We need energy in every form or the other to sustain or to carry out any work. From the naturally gifted resources, we get energy in one form or the other, for example, coal, petroleum, sunlight, etc. It is our duty to preserve and protect these resources. Judicious use of energy is very important to keep the resources available for future generations.

 

Chapter 4 Work And Energy Track Your Learning Question And Answers

Question 1. ______ is defined as the capacity of doing work.

1. Work
2. Energy
3. Power
4. None

Answer. 2. Energy

Question 2. The main source of energy is ______, which gives energy to all the entities of the universe either directly or indirectly.

1. Sun
2. Sea
3. Ocean
4. Coal

Answer. 1. Sun

Question 3. The energy used in households, industries and commercial establishments is usually expressed in:

1. Joules
2. Watt
3. Kilowatt hour
4. None of the options

Answer. 3. Kilowatt hour

Question 4. The largest group of geothermal power plants in the world are located in ______.

1. Germany
2. India
3. United States
4. UK

Answer. 3. United States

Question 5. Tidal energy uses rise and fall of tides to convert ______ energy of incoming and outgoing tides into electrical energy.

1. Potential
2. Mechanical
3. Electrical
4. Kinetic

Answer. 4. Kinetic

Question 6. When the speed of a bike increases by 120%, then its kinetic energy increases by:

1. 4.84 times
2. 3 times
3. 1.44 times
4. By 240 %

Answer. 1. 4.84 times

Question 7. How fast should a man of 50 kg run so that his kinetic energy reaches 500 J?

1. 5 m/s
2. 10 m/s
3. 20 m/s
4. 2(5)1/2 m/s

Answer. 4. 2(5)1/2 m/s

Chapter 4 Work And Energy Rate of Doing Work

We all consume energy at some rate. Therefore, rate of consuming energy is called power. Power measures the speed of work done, that is, how fast or slow the work is done. Power is defined as the rate of doing work or the rate of transfer of energy. If an agent does a work W in time t, then power is given by:

\(\text { Power }=\frac{\text { work }}{\text { time }} \text { or } P=\frac{W}{t}\)

The unit of power is watt having the symbol W. 1 watt is the power of an agent, which does work at the rate of 1 joule per second. We can also say that power is 1 W when the rate of consumption of energy is 1 J s^-1. 1 watt = 1 joule/second or 1 W = 1 J s^-1. We express larger rates of energy transfer in kilowatts (kW).

1 kilowatt = 1000 watts

1 kW = 1000 W

1 kW = 1000 J s^-1

Key Points to Remember

1. Work done on an object is defined as the magnitude of the force multiplied by the distance moved by the object in the direction of the applied force. The unit of work is joule: 1 joule = 1 newton × 1 metre.
2. Work done on an object by a force would be zero if the displacement of the object is zero.
3. An object having capability to do work is said to possess energy. Energy has the same unit as that of work.
4. An object in motion possesses what is known as the kinetic energy of the object. An object of mass, m moving with velocity v has a kinetic energy of \(\frac{1}{2} m V^2\).
5. The energy possessed by a body due to its position called the potential energy. The gravitational potential energy of an object of mass, m raised through a height, h from the earth’s surface is given by mgh.
6. According to the law of conservation of energy, energy can only be transformed from one form to another; it can neither be created nor destroyed. The total energy before and after the transformation always remains constant.
7. Energy exists in nature in several forms such as kinetic energy, potential energy, heat energy, chemical energy etc. The sum of the kinetic and potential energies of an object is called its mechanical energy.
8. Power is defined as the rate of doing work. The SI unit of power is watt. 1 W = 1 J/s.
9. The energy used in one hour at the rate of 1kW is called 1 kW h.

Chapter 4 Work And Energy Very Short Question and Answers

Question 1. Define power. What is the SI unit of power?
Answer:

Power:

Power is defined as total work done divided by total time taken. The SI unit of power is Watt.

Question 2. What is the commercial unit of energy? Convert it into Js^-1
Answer:

Commercial unit of energy:

The commercial unit of energy is kilowatt-hour (kWh).

Question 3. A boy of mass 60 kg runs up a staircase of 50 steps in 10 s. If the height of each step is 10 cm, find his power. Take g = 10 m s^-2.
Answer:

Given

A boy of mass 60 kg runs up a staircase of 50 steps in 10 s. If the height of each step is 10 cm

Weight of the boy = mg = 60 × 10 ms^-2

= 600 N

Height of the staircase,

h = 50 × 10/100 m

= 5 m

Time taken to climb = 10 s

P = work done/time

P = mgh/t

P = 600 × 5/10 s

P = 300 W

Thus, power is 300 W.

Question 4. An electric bulb of 60 W is used for 6 h per day. Calculate the ‘units’ of energy consumed in one day by the bulb.
Answer:

Given

Power of electric bulb = 60 W

= 0.06 kW.

Time used,

t = 6 h

Energy = power × time taken

= 0.06 kW × 6 h

= 0.36 kWh

= 0.36 ‘units’.

The energy consumed by the bulb is 0.36 ‘units’.

Chapter 4 Work And Energy

Question 1. A pump transfers 500 L of water to the overhead tank of a building of height 12 m in 15 minutes. Calculate the power of motor pump.
(Take g = 10 ms^-2) (Mass of 1 L of water = 1 kg)

1. P = 66.7 W
2. P = 68 W
3. P = 72 W
4. P = 83 W

Answer. 1. P = 66.7 W

Question 2. A machine does 192 J of work in 12 Sec. What is the power of the machine?

1. 8 W
2. 2 W
3. 16 W
4. 10 W

Answer. 3. 16 W

Question 3. A weighting 500 kg runs up a hill rising himself vertically 10 m in 40 Sec. Calculate power. given g = 9.8 m^-1

1. 1220 W
2. 2000 W
3. 1623 W
4. 1225 W

Answer. 2. 2000 W

Question 4. A rickshaw puller pulls the rickshaw by applying a force of 200 N. If the rickshaw moves with constant velocity of 10 ms^-1. Find the power of rickshaw puller.

1. 2220 W
2. 2000 W
3. 2623 W
4. 1005 W

Answer. 2. 2000 W

Question 5. Calculate the time taken 60 W bulb to consume 3600 J of energy.

1. 3 min
2. 60 min
3. 6 min
4. 1 min

Answer. 4. 1 min

Chapter 4 Work And Energy Practice Exercises

Question 1. When a body falls freely towards the earth, then its total energy

1. increases
2. decreases
3. remains constant
4. first increases and then decreases

Answer. 3. remains constant

Question 2. A car is accelerated on a levelled road and attains a velocity 4 times of its initial velocity. In this process the potential energy of the car

1. does not change
2. becomes twice to that of initial
3. becomes 4 times that of initial
4. becomes 16 times that of initial

Answer. 1. does not change

Question 3. In case of negative work the angle between the force and displacement is

1. 0°
2. 45°
3. 90°
4. 180°

Answer. 4. 180°

Question 4. An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass is 3.5  kg. Both spheres are dropped simultaneously from a tower. When they are 10m above the ground, they have the same

1. acceleration
2. momenta
3. potential energy
4. kinetic energy

Answer. 1. acceleration

Question 5. A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a levelled road. The work done against the gravitational force will be (g = 10 m s^-2)

1. 6 × 103 J
2. 6 J
3. 0.6 J
4. zero

Answer. 4. zero

Question 6. Which one of the following is not the unit of energy?

1. joule
2. newton metre
3. kilowatt
4. kilowatt hour

Answer. 3. kilowatt

Question 7. The work done on an object does not depend upon the

1. displacement
2. force applied
3. angle between force and displacement
4. initial velocity of the object

Answer. 4. initial velocity of the object

Question 8. Water stored in a dam possesses

1. no energy
2. electrical energy
3. kinetic energy
4. potential energy

Answer. 4. potential energy

Question 9. A body is falling from a height h. After it has fallen a height h/2 it will possess

1. only potential energy
2. only kinetic energy
3. half potential and half kinetic energy
4. more kinetic and less potential energy

Answer. 3. half potential and half kinetic energy

Chapter 4 Work And Energy Fill in the Blanks

Question 1. If force and displacement are in the same direction, the work would be ______.
Answer. Positive

Question 2. The work done on a 5 kg body to displace it by ______ is 5 J, given that force applied is 1 N.
Answer. 5 m

Question 3. Work done on a body get stored as ______.
Answer. Potential energy

Question 4. A bird sitting at a height has only ______ energy.
Answer. Potential

Question 5. Kinetic energy is a ______ quantity.
Answer. Scalar

Question 6. If the speed of a body is doubled, its kinetic energy must become ______.
Answer. Four times

Question 7. The sum of potential energy and kinetic energy is called ______ energy.
Answer. Mechanical

Question 8. When a ball is thrown up, ______ energy is converted into potential energy.
Answer. Kinetic

Question 9. Electricity is measured by electric meters installed in our homes that measure electric energy in units of ______.
Answer. Kilowatt-hour (kWh)

Question 10. Energy is a ______ quantity.
Answer. Scalar

 

Chapter 4 Work And Energy Match the Columns

Question 1. Match the column 1 with 2.

Select the correct option:

1. A-3, B-1, C-4, D-2
2. A-4, B-3, C-2, D-1
3. A-3, B-4, C-1, D-2
4. A-1, B-3, C-2, D-4

Answer. 2. A-4, B-3, C-2, D-1

Question 2. Match the column 1 with 2.

Select the correct option:

1. A-2, B-3, C-4, D-1
2. A-4, B-3, C-2, D-1
3. A-3, B-4, C-1, D-2
4. A-1, B-3, C-2, D-4

Answer. 1. A-2, B-3, C-4, D-1

Chapter 4 Work And Energy Assertion Reasoning

Direction: Choose the correct answer from the following choices:

1. Assertion and reason are both correct statements and reason is explanation for assertion.
2. Assertion and reason are both correct statements but reason is not the correct explanation for assertion.
3. Assertion is correct statement but reason is incorrect statement.
4. Assertion is incorrect statement but reason is correct.

Question 1. Assertion (A): Humans are machines, they can do lot of work.
Reason (R): People are able to do work because of energy.
Answer. 1. Assertion and reason are both correct statements and reason is explanation for assertion.

Question 2. Assertion (A): Thus, work done by force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force.
Reason (R): Work has both magnitude and direction.
Answer. 3. Assertion is correct statement but reason is incorrect statement.

Question 3. Assertion (A): Work done is negative when the force acts opposite to the direction of displacement.
Reason (R): Work done is positive when the force is in the direction of displacement.
Answer. 2. Assertion and reason are both correct statements but reason is not the correct explanation for assertion.

Question 4. Assertion (A): The energy possessed by an object is measured in terms of its capacity of doing work.
Reason (R): The unit of energy is, therefore, the same as that of work, that is, joule (J).
Answer. 1. Assertion and reason are both correct statements and reason is explanation for assertion.

Question 5. Assertion (A): Flowing water, ­blowing wind, a running athlete, etc., possess kinetic energy.
Reason (R): Kinetic energy is the energy possessed by an object due to its motion.
Answer. 1. Assertion and reason are both correct statements and reason is explanation for assertion.

Chapter 4 Work And Energy Comprehension Passage

An object at a certain height possess potential energy. Now, work is done on it, against the gravity by bringing the object to some other point.

Gravitational potential energy of an object above the ground at a certain point is defined as raising the body to that point against the gravity.

Let us try to devise a formula to calculate the potential energy.

Consider an object of mass m. Let it be raised through a height h from the ground. A force is required to do this. The minimum force required to raise the object is equal to the weight of the object mg.

The object gains energy equal to the work done on it. Let the work done on the object against gravity be W. That is, work done.

W = force × displacement

= mg × h

= mgh

Since work done on the object is equal to mgh, energy equal to mgh units is gained by the object. This is the potential energy (EP) of the object.

E_p = mgh

Question 1. When a body is raised above the ground against gravity, which energy is used?

1. Potential energy
2. Kinetic energy
3. Gravitational potential energy
4. Gravitational kinetic energy

Answer. 3. Gravitational potential energy

Question 2. ‘Mgh’ is the formula for

1. Kinetic energy
2. Potential energy
3. Both (a) and (b)
4. None of the above

Answer. 2. Potential energy

Chapter 4 Work And Energy Integer Type Question And Answers

Question 1. Calculate the kinetic energy of the body of mass 4 kg moving with the velocity of 0.1 metre per second.
Answer. 0.02 J

Question 2. How much work is done by a force 20 N in moving an object through a distance of 2 m in direction of the force?
Answer. 40 J

Question 3. What is the work to be done to increase the velocity of a car from 20 km h-1 to 40 km h^-1 if the mass of the car is 1200 kg?
Answer. 2.22 x 105 J

Question 4. 10 tube lights each of 50 W are operated for 15 hours. Calculate electrical energy consumed in ‘units’.
Answer. 7.5 kWh

Question 5. Rahul, having her own mass 50 kg, climbs 20 m height along with 30 kg mass in 40 s. Calculate her power and work done. (take g = 10 m/s²)
Answer. W = 16 kJ P = 400 W

Chapter 4 Work And Energy Very Short Question and Answers

Question 1. Define energy and its commercial unit. Express it in terms of Joules.
Answer:

Energy and its commercial unit.:

Energy is defined as the capacity of doing work. The commercial unit of energy is kilowatt-hour.

1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J

Question 2. How are resources classified?
Answer:

Classification Of resources:

When energy source used is easily replenished in a short period and the reserve is limitless is called renewable source. The sources of energy which are limited in quantity and are exhaustible are called non-renewable sources of energy.

Question 3. Name the different sources of energy.
Answer:

The different sources of energy

The five sources of energy are solar energy, wind energy, geothermal energy, hydroelectric energy and biomass energy

Question 4. What are the different forms of energy?
Answer:

Different forms of energy:

The various forms include mechanical energy (potential energy + kinetic energy), chemical energy, heat energy, light energy and electrical energy.

Question 5. Define mechanical energy and its types.
Answer:

Mechanical energy and its types:

Mechanical energy is of two types i.e., the energy possessed by a body due to its motion is called kinetic energy. The energy possessed by a body due to its position or height is called potential energy.

Question 6. Define conservative and non-conservative sources of energy.
Answer:

Conservative and non-conservative sources of energy:

If the work done by a force depends only on initial and final positions but not on the path taken, then the force is said to be conservative. If the work done by a force depend on the path taken then the force is said to be non-conservative.

Question 7. Define law of conservation of energy.
Answer:

Law of conservation of energy:

Energy can neither be created nor destroyed. It can only be changed from one form to another.

Question 8. A car is moving with the uniform velocity of 50 km/h. What is the kinetic energy of the object of mass 40 kg kept in the car?
Answer:

Given:

A car is moving with the uniform velocity of 50 km/h.

We know that both objects and car are moving with the same velocity

i.e., v = 50 km/h = 50 × 103/(60 × 60)

= 13.88 m/s²

Mass of the object,

m = 40 kg

K.E. = \(\frac{1}{2} m V^2\)

K.E. = \(\frac{1}{2} \times 40 \times(13.88)^2\)

K.E. = 3853.08 J

The kinetic energy of the object of mass 40 kg kept in the car is 3853.08 J

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Question 9. The acceleration due to gravity is 20 m/s², what will be the potential energy of a body of mass 1 kg kept at the height of 10 m?
Answer:

Given:

The acceleration due to gravity is 20 m/s²,

Potential Energy = mgh

Mass, m = 1 kg

Acceleration due to gravity,

g = 20 m/s²

Height, h = 10 m

Potential Energy = 1 × 20 × 10

= 200 J

Hence, potential energy is 200 Joules.

Question 10. Calculate potential energy of water in a tank having l = 4 m, b = 3 m and h = 2, situated on top of a house whose height is 9 m.
Take rw = 1 x 10³ kg/m³ and g = 10 ms^-2
Answer:

Given

l = 4 m, b = 3 m and h = 2, situated on top of a house whose height is 9 m.

Take rw = 1 x 10³ kg/m³ and g = 10 ms^-2

Volume of water = Volume of tank

= lbh

= 4 m × 3 m × 2 m

= 24 m³

Mass of water = Volume of density

= 24 × 10³ kg

Mean height of water above the ground

H = h₁ + h₂

= 9 m + 1 m

= 10 m

Therefore, Potential energy = MgH

= 24 × 10³ × 10 × 10

= 24 × 10⁵ J

Potential energy of water in a tank = 24 × 10⁵ J

Question 11. A body of mass 0.5 kg is in rest at a height of 20 m above the ground.

1. Find its total energy.
2. What is the total energy, if it starts falling freely and has fallen through a height of 5 m? (Take g = 10 ms^-2)
3. What conclusion can be drawn from these calculations?

Answer:

(1) P.E. of the body = mgh

= 0.5 × 10 × 20

= 100 J

K.E. of the body = \(\frac{1}{2} m V^2\)

= \(\frac{1}{2} \times 0.5 \times 0\)

= 0

Total energy = P.E. + K.E.

= 100 + 0

= 100 J

∴ Total energy = 100 J

(2)

Velocity of the body at point B is given by

v² = u² + 2aS

= 0 + 2 × 10 × 5

= 100

∴ v = 10 ms^-1

∴ Its K.E. at point B = \(\frac{1}{2} m V^2\)

= \(\frac{1}{2} \times 0.5 \times(10)^2\)

= \(\frac{1}{2} \times 0.5 \times 100\)

= 25 J

Its P.E. at point B = mgh2

= 0.5 × 10 × 15

= 75 J

Its total energy at point B = K.E. + P.E.

= 25 J + 75 J

= 100 J

Thus, we find that the total energy of a freely falling body remains constant, though its potential energy gradually change into kinetic energy.

Question 12. Calculate the kinetic energy of a body of mass 4 kg moving with the velocity of 0.2 meter per second.
Answer:

Kinetic Energy = \(\frac{1}{2} m V^2\)

Here mass = 4 kg

Velocity = 0.2 m/s

So, by putting the values in formula:

Kinetic energy = \(\frac{1}{2} \times 4 \times(0.2)^2\)

= \(\frac{1}{2} \times 4 \times 0.2 \times 0.2\)

= 0.08

The kinetic energy of a body = 0.08

Question 13. Define work and its types.
Answer:

Work and its types:

If a force is applied on a body which led to displacement in the body then work is done. Work is the product of magnitude of force and displacement.

Positive work: If a force is applied in the same direction to displacement, then work done is said to be positive.

Negative work: If a force is applied in the opposite direction of displacement, then work done is said to be negative.

Question 14. A swimmer makes a swing jump between two points, by holding one end of a rope, other end of which is tied to some higher point. What type of work is done by rope in jumping of the swimmer from one point to another?
Answer:

Zero work done.

Question 15. Calculate the work done in operating the crane, if it lifts a mass of 1600 kg through a vertical height of 40 m. 
Answer:

Given

The crane, if it lifts  A mass of 1600 kg through a vertical height of 40 m

g = 9.8 m/s²

F = mg = 1600 kg × 9.8 m/s²

= 15680 N

W = F × S = 15680 N × 40 m = 627,200 J

Work done in operating the crane = 627,200 J

Question 16. How much work is done by a force of 15 N in moving an object through a distance of 2 m in the direction of force?
Answer:

Given

Force of 15 N in moving an object through a distance of 2 m in the direction of force

W = F × S

Hence force, F = 15 N

Distance, S = 2 m

Work done, W = 15 × 2

W = 30 Joules

∴ Work done = 30 Joules