NCERT Solutions for Class 10 Science Chapter 14- Sources of Energy

NCERT Solutions for Class 10 Science Chapter 14- Sources of Energy

Q. What is a good source of energy?

Answer: A good source of energy is one that

a) does a large amount of work per unit volume or mass

b) can be easily accessible

c) is easy to store and transport, and

d) is economical.

Q. What is a good fuel?

Ans: A fuel is said to be good when it is easily available and when it produces a large amount of heat energy when burnt.

Q. Write the characteristics of a good fuel.


a. It should possess a high calorific value.

b. It should have a proper ignition temperature.

c. It should not produce poisonous products during combustion.

d. It should have a moderate rate of combustion.

e. Combustion should be easily controllable

f. It should not leave behind much ash in combustion.

g. It should be cheap.

h. It should be easy to transport.

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

Answer: I would prefer to use cooking gas like LPG. It fulfills many of the criteria of a good fuel like its ignition temperature, good calorific value, and non-polluting characteristics.

Q. What are fossil fuels?

Ans: A natural fuel formed deep under the earth from the remains of living organisms is called fossil fuel.

Q. Write the advantages of fossil fuels.

Ans: Advantages of fossil fuels:

a. It is a cheap Source of Energy

b. It is safe to Transport

c. It has a high Calorific Value

d. It is available in plenty

Q. Write the disadvantages of fossil fuels.

Answer: Disadvantages of fossil fuels.

(i) The burning of fossil fuels produces large amount of carbon dioxide that causes increased greenhouse effect.

(ii) The burning of fossil fuels (such as coal) produces smoke which pollutes the air.

(iii) The burning of fossil fuels produces acidic gases such as sulphur dioxide and nitrogen oxide. These acidic gases cause acid rain that affects our water and soil resources.

(iv) Fossil fuels cannot be replenished in short time because it takes millions of years to form them.

Q. Why are we looking at alternate source of energy?

Ans: As fossil fuels are being used at large scale and they are non renewable sources of energy, they will disappear after some time. After the depletion of non renewable sources of energy we will be left with nothing, hence we are trying to develop alternate sources of energy.

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

Ans: Windmill farms are constructed to produce electricity.

The traditional use of energy from flowing water has been modified by establishing hydro-power plants. At hydro-power plants, the energy of falling water or flowing water is tapped by using a water turbine and then made to drive generators.

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

Ans: A concave mirror would be best suited in a solar cooker because it focuses the sunlight in a very small area of the solar cooker and a high temperature is produced in it which is sufficient to cook the food.

Q. What are the limitations of the energy that can be obtained from the ocean?

Ans: The different forms of energy that can be obtained from the ocean are tidal energy, wave energy and ocean thermal energy. Following are the limitations of the energy obtained from ocean:

a) The relative positioning of the earth, the sun and the moon has an impact on the tidal energy.

b) For the conversion of tidal energy into electricity, high dams are required.

c) To obtain electricity from wave energy, very strong waves are required.

Q. What is geothermal energy?

Ans. The heat energy obtained in the form of steam from under the earth’s crust is called geothermal energy.

Q. What are the advantages of nuclear energy?

Ans: Following are the advantages of nuclear energy:

a) The amount of energy produced per unit mass is large

b) It is a cleaner form of energy as it does not produce any pollutants.

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

Ans: No source of energy can be called pollution-free, because, the use of any source of energy disturbs the environment in one way or the other. A source of energy like a solar cell is pollution free in actual operation but the assembly of the device might have caused some damage to the environment. So, in an absolute sense, no source of energy can be called pollution free.

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

Ans: Hydrogen is a cleaner fuel than CNG. This is because the burning of hydrogen produces only water, which is totally harmless. On the other hand, the burning of CNG produces carbon dioxide gas and water. The carbon dioxide can produce a greenhouse effect in the atmosphere and lead to the excessive heating of the environment in long run.

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

Ans: (i) Energy derived from biomass is a renewable source of energy because waste products are continuously produced. Plants and trees are also grown at reasonable intervals.

(ii) The energy derived from flowing water, wind, sun and ocean are renewable sources because these sources can be harnessed into energy so long as the present solar system exists.

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

Ans: Fossil fuels such as coal and petroleum are two energy sources that are exhaustible because they are only limited reserves. Fossil fuels are non-renewable sources of energy. So we need to conserve them.

Q. A solar water heater cannot be used to get hot water on

(a) a sunny day

(b) a cloudy day

(c) a hot day

(d) a windy day

Answer: (b) A cloudy day.

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

(a) Wood

(b) Gobar gas

(c) Nuclear energy

(d) Coal

Answer: (c) Nuclear energy.

Q. 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?

(a) Geothermal energy

(b) Wind energy

(c) Nuclear energy

(d) Biomass

Answer: (a) Geothermal energy.

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


Fossil fuelsSun
(i) Non-renewable source of energy.(i) Renewable source of energy.
(ii) Cause a lot of air pollution.(ii) Pollution-free, doesn’t cause any pollution.
(iii) They will exhaust in the future.(iii) It is a non-exhaustible source.
(iv) Energy can be tapped throughout the year.(iv) Energy cannot be tapped during the night and on cloudy and rainy days.

Q. Compare and contrast biomass and hydro-electricity as sources of energy.


(i) Renewable source of energy.(i) Renewable source of energy.
(ii) Biomass plants can be installed at any place to produce biomass as energy source.(ii) Plants can be installed only at the places where dams can be constructed.
(iii) To collect waste materials is a tough and costly process.(iii) Once the plants start to work, it is not difficult to collect water.

Q. What are the limitations of extracting energy from

(a) the wind?

Answer: Limitations of wind energy

(i) Wind energy farms cannot be established everywhere. Wind energy farms can be established only at those places, where the wind blows for the most part of the year.

(ii) The wind required for generating electricity should be strong and steady to maintain the desired level of generation. The minimum wind speed necessary for the satisfactory working of the wind generator is about 15 km/h. This is not always so.

(iii) Wind energy farms require a large area of land.

(iv) The setting up of wind energy farms is very expensive.

(b) waves?

Ans: Limitations of wave energy: The harnessing of sea-waves energy would be a viable proposition only at those places where sea waves are very strong. This has constraints of time and location.

(c) tides?

Ans: Limitations of tidal energy :
(i) There are very few sites around the world that are suitable for building tidal dams.
(ii) The rise and fall of sea water during high and low tides is not enough to generate electricity on a large scale.

Q. On what basis would you classify energy sources as

(a) renewable and non-renewable?

(b) exhaustible and inexhaustible?

Are the options given in (a) and (b) the same?

Answer: (a) Renewable sources: The sources of energy that are being produced continuously in nature and are inexhaustible, are called renewable sources of energy. The energy derived from flowing water, wind, tides, ocean waves, or wood are examples of energy from such sources.

Non-renewable sources: These sources are produced over millions of years under special conditions. Once consumed, these are not replaceable for a very long time. Fossil fuels like coal, petroleum, and natural gas are non-renewable sources.

(b) Exhaustible sources are non-renewable sources, while inexhaustible sources are renewable sources.
Yes, the options given in (a) and (b) are the same.

Q. What are the qualities of an ideal source of energy?

Ans. The ideal source should have the following qualities:

a) It is easy to handle.

b).  It can be transported easily.

c) It should have maximum calorific value.

d) It should have a proper ignition temperature.

e) It should not cause any environmental pollution.

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

Ans. Advantages of solar cooker:

(a) It is cheap and easy to handle.

(b) It does not need any fuel for cooking food.

(c) It is pollution free.

Disadvantages of solar cooker:

(a) It is very slow, takes long time for cooking.

(b) It is dependent on sun’s light, cannot work on cloudy day.

(c) The reflectors position need to be monitored so as it reflects the sunlight at the centre focused point of the solar cooker.

Yes-the places where sun’s energy not sufficient, the use of solar cookers would be limited

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

Ans: Some of the environmental consequences of the increasing demand for energy are the following:

  1. The combustion of fossil fuels is producing acid rain and damaging plants (crops), soil, and aquatic life.
  2. The burning of fossil fuels is increasing the amount of greenhouse gas carbon dioxide in the atmosphere. It has also affected the rainfall.
  3. The cutting down of trees from the forest for obtaining firewood is causing soil erosion and destroying wildlife.
  4. The construction of hydro-power plants is disturbing the ecological balance.
  5. Nuclear power plants are increasing radioactivity in the environment.

The following steps can be taken to reduce energy consumption :

  1. Switch off lights, fans, and TV. and other such electrical appliances when not needed, to save electricity.
  2. Use energy-efficient electrical appliances to save electricity. This can be done by using compact fluorescent lamps (CFL) and tube lights in place of conventional filament-type electric bulbs.
  3. Good quality stoves should be used to burn fuels like kerosene and LPG so as to obtain maximum heat.
  4. Pressure cookers should be used for cooking food to save fuel.
  5. Solar cookers should be used to cook food whenever possible and solar water heaters should be used to get hot water.
  6. The use of biogas as fuel should be encouraged in rural areas.
  7. Bicycles should be used for short distances to save fuel like petrol which is used in cars, scooters and motorcycles.

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