NCERT Solutions for Class 10 Science Chapter 16 - Sources of Energy

Question 1:

What is a good source of energy?


A good source of energy is the one which:
(i) releases a large amount of heat per unit mass
(ii) is easily available
(iii) does not cost much
(iv) can be easily transported from one place to another

Question 2:

What is a good fuel?


(i) It should have a high calorific value.
(ii) It should be economical.
(iii) It should have a low ignition temperature.
(iv) It should be easy to store and transport.
(v) It should burn at a controllable rate.

Question 3:

If you could use any source of energy for heating your food, which one would you use and why?


The fuel to be used should be easily accessible and should be easy to store and transport. The fuel should also be economical.
If we are in a city, LPG should be used since it does not produce pollution, is easily available and is economical.
In rural areas, gobar gas should be used. It is almost free, has high calorific value and is almost pollution free. It is also a renewable source of energy.

Question 4:

What are the disadvantages of fossil fuels?


Though fossil fuels are used as a source of energy on a large scale, still, there are a number of disadvantages of using them.
(i) There are only limited reserves of fossil fuels. These fuels were formed from the remains of dead plants and animals over millions of years. If we continue to use them at the present rate, we would soon run out of energy.
(ii) Fossil fuels are non-renewable sources of energy.
(iii) Fossil fuels cause air pollution.
(iv) Oxides of carbon, nitrogen and sulphur released on burning of the fossil fuels are acidic oxides. These lead to acid rain, affecting water and soil resources.
(v) Carbon dioxide produced by the burning of fossil fuels causes greenhouse effect.

Question 5:

Why are we looking for alternative sources of energy?


We are looking for alternative sources of energy because the conventional sources of energy, like coal and petroleum, are not going to last long, cause pollution and are costly.

Question 6:

How has the traditional use of wind and water energy been modified for our convenience?


The energy of the wind can be utilised using windmills. Windmill uses wind energy. Energy of the wind can be used to do mechanical work i.e., to lift water from the well or run a grain-grinding machine. Water energy can be used to produce electric power in hydro power plants. The water is collected in dams. The potential energy of the stored water changes into kinetic energy of the flowing water, which is used to run turbines, thereby generating electricity. Energy of the tides in the sea can also be converted into electricity. During high tides, the water is stored and during low tides, the energy of the stored water is used to convert it into electricity.

Question 7:

What kind of mirror, concave, convex or plane, would be best suited for use in a solar cooker? Why?


A concave mirror is best suited since it can focus sun rays from a large area to a specific area. However, a plane mirror can also be used but a convex mirror is never used. A convex mirror diverges the rays and hence, will not transfer sufficient heat to the cooker.

Question 8:

What are the limitations of the energy that can be obtained from the oceans?


Due to the attraction of the moon, there are high and low tides in the sea. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy into electricity. The limitation of such dams is the scarcity of locations where such dams can be constructed.
The ocean thermal energy of the sea or the ocean is also used to produce electricity but these plants operate only if the temperature difference between the water at the surface and the water at a depth up to 2 km is 20°C or more.

Question 9:

What is geothermal energy?


Due to the changes taking place within the earth, molten rocks formed in the deeper hot regions of the earth are pushed upward in the regions called ‘hot spots’. Steam is generated when underground water comes in contact with the hot spots. The steam trapped in the rocks is routed through a pipe to the turbine and is used to generate electricity. Though the cost is not much, the commercially suitable sites have to be located.

Question 10:

What are the advantages of nuclear energy?


Nuclear energy is preferred over fossil energy, hydro energy, thermal energy etc. for the following reasons:
1. A smaller space is required to harness nuclear energy as compared to the space required to harness hydro energy, thermal energy etc.
2. It produces much more energy than the other conventional sources.
3. It costs less.

Question 11:

Can any source of energy be pollution free? Why or why not?


No, source of energy can be perfectly pollution free but, hydro energy, wind energy, geothermal energy, solar energy are considered as pollution free, though their construction causes pollution.

Question 12:

Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?


Hydrogen is a cleaner fuel than CNG, because it does not pollute the atmosphere. Hydrogen, when burnt in the presence of oxygen, produces harmless water vapours. On the other hand, CNG, when burnt, produces carbon monoxide, carbon dioxide and oxides of sulphur and nitrogen.

Question 13:

Name two energy sources that you would consider to be renewable. Give reasons for your choice.


Solar energy and wind energy are renewable sources of energy. Solar energy is free and can be used anywhere with ease. It can be used to produce electric energy through solar cells. It can be used in solar water heaters and in solar cookers.
Wind is also a renewable source of energy and can be used to run wind farms to produce electricity, to draw water from the wells and to grind the grains.

Question 14:

Give names of two energy sources that you would consider to be exhaustible. Give reasons for your choice.


Coal and petroleum are two energy sources which are exhaustible. It takes millions of years for the formation of petrol and coal inside the earth. Their reserves are limited. Coal, if used at present rate, will not last beyond 200 years whereas petroleum products, which are being extensively used, are not expected to last for more than 50 years. Wood, though considered to be a renewable source of energy, should be used with at most caution. Because, to use wood as a fuel, many trees have to be cut down and it takes more than 10 years for a tree to grow up.

Question 15:

A solar water heater cannot be used to get hot water on a

  1. sunny day
  2. cloudy day
  3. hot day
  4. windy day

Cloudy day is correct. The sun must be shining for a solar water heater to work effectively.

Question 16:

Which of the following is not an example of a biomass energy source?

  1. wood
  2. gobar-gas
  3. nuclear energy
  4. coal

Nuclear energy

Question 17:

Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the sun’s energy?

  1. geothermal energy
  2. wind energy
  3. nuclear fuel
  4. bio-mass

Nuclear fuels are not derived from the sun’s energy.

Question 18:

Compare and contrast fossil fuels and the sun as direct sources of energy.


1. Both are natural sources of energy.
2. Both are widely used sources of energy.
3. Minimum technology is required to get energy from either of these sources. Dissimilarities/Contrasts:
1. The sun’s energy can be used only during the day but energy from the fossil fuels can be used any time.
2. Solar energy is almost free whereas energy production from fossil fuels costs much.
3. An infinite amount of solar energy is available almost free of cost whereas there is a limited stock of fossil fuels.
4. Solar energy is a renewable source of energy whereas it takes millions of years to produce fossil fuels.
5. Solar energy is totally pollution free whereas fossil fuels produce a lot of pollution.

Question 19:

Compare and contrast biomass and hydroelectricity as sources of energy.


1. Hydroelectricity is totally pollution free whereas biomass source produces a very little pollution, if properly used.
2. Both are renewable sources of energy.
3. The working cost of both the sources is very low. However, the initial cost of hydroelectric source is more than that of biomass source.

1. A large area of land gets submerged under water in a hydroelectric plant whereas a very small area is used for biomass plants.
2. Specific location is required for hydroelectric plants. These can only be established at very high altitudes. Biomass plants can be established almost anywhere.
3. The energy produced from a hydroelectric plant is much more than the energy produced from a biomass plant.

Question 20:

What are the limitations of extracting energy from
(a) the wind,
(b) waves
(c) tides?


(a) The limitations of extracting energy from the winds:
1. It requires a lot of space.
2. It is not available everywhere and at all times.
3. Wind velocity must be sufficient. It should never be less than 15 kmh–1.
(b) The limitations of extracting energy from the waves:
1. Waves are possible only when a strong wind is blowing over the surface of the sea.
2. It is very costly and is difficult to manage.
(c) The limitations of getting energy from the tides:
1. Its cost is high.
2. It is difficult to maintain and operate tidal wave dams deep in the sea.
3. A huge amount of salt gets deposited on the base of the dam.

Question 21:

On what basis would you classify the energy sources as
(a) renewable and non-renewable? (b) exhaustible and inexhaustible?
Are the options given in (a) and (b) the same?


The sources of energy that will get depleted someday are said to be exhaustible sources or nonrenewable sources of energy.
The sources from which we can be assured of constant supply of energy at a particular rate i.e., the sources which can be regenerated are called renewable sources of energy. We are receiving energy from the sun for the past five billion years and we will continue receive it for another five billion years; therefore, we can say that the solar energy is inexhaustible or renewable.
The coal reserves with us are for about 200 years whereas it will take millions of years for it to form again; hence, coal is said to be an exhaustible or a non-renewable source of energy. Hence options given in (a) and (b) are not same.

Question 22:

What are the qualities of an ideal source of energy?


The properties of an ideal source of energy are:
1. It should not cause any pollution.
2. It should be readily available at an economical rate.
3. It should be easy to store and should not produce any hazard during transportation.
4. It should evolve energy at a controllable rate.
5. It should not leave any residue.

Question 23:

What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?


The advantages of using solar cooker:
1. It does not produce any pollution.
2. It saves fuel.
3. Since the food is cooked at a comparatively low temperature, hence the nutrients in the food are not destroyed during the cooking.
4. More than one items can be cooked at the same time.
The limitations of using solar cooker:
1. Solar energy is not available in sufficient amount at all the times. It cannot be used at night time and on cloudy days.
2. The direction of the solar cooker has to be changed again and again.
3. It cannot be used for frying purpose.
4. It cannot cook chapattis.
5. Solar cookers cannot be used at places where there is insufficient amount of sunshine.

Question 24:

What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?


The demand for energy is increasing day by day. Exploiting any source of energy may disturb the environment in one way or the other. For example, getting energy from the fossil fuels may cause a lot of pollution in the air or the construction of dams on the rivers destroys large ecosystems. The steps for reducing energy consumption should be such that we can obtain maximum energy through minimum consumption of the fuels. For this:
1. Under the given situation, technology utilized should be the best possible. For example, using smokeless chulha should be preferred over the traditional chulhas.
2. The fossil fuels should be used with care to derive the maximum benefit out of them.
3. The wastage of energy should be strictly avoided.
4. The sources of energy should be such that they cause minimum damage to the environment.