NCERT solutions of class 10 chapter 14 sources of energy science
In text questions
Page no. 243
Question 1: What is a good source of energy?
Answer: A good source of energy fulfils the following criteria:
(I)It produces a lot of heat per unit mass.
(II) It does a huge amount of work per unit mass.
(III) It is easily accessible.
(IV) It is easy to store and transport.
(V)It is economical.
(VI)It produces less amount of smoke.
Question 2: What is a good fuel?
Answer: A good fuel produces a huge amount of heat on burning, does not produce a lot of
smoke, and is easily available.
Question 3: If you could use any source of energy for heating your food, which one would you use
and why?
Answer: Natural gas can be used for heating and cooking food because it is a clean source of
energy. It does not produce huge amount of smoke on burning. Although it is highly
inflammable, it is easy to use, transport, and it produces a huge amount of heat on
burning.
In text questions
Page no. 243
Question 1: What is a good source of energy?
Answer: A good source of energy fulfils the following criteria:
(I)It produces a lot of heat per unit mass.
(II) It does a huge amount of work per unit mass.
(III) It is easily accessible.
(IV) It is easy to store and transport.
(V)It is economical.
(VI)It produces less amount of smoke.
Question 2: What is a good fuel?
Answer: A good fuel produces a huge amount of heat on burning, does not produce a lot of
smoke, and is easily available.
Question 3: If you could use any source of energy for heating your food, which one would you use
and why?
Answer: Natural gas can be used for heating and cooking food because it is a clean source of
energy. It does not produce huge amount of smoke on burning. Although it is highly
inflammable, it is easy to use, transport, and it produces a huge amount of heat on
burning.
Question 1: What are the disadvantages of fossil fuels?
Answer: The disadvantages of fossil fuels are as follows:
(a) Burning of coal and petroleum produces a lot of pollutants causing air pollution.
(b) Fossil fuels release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain,
which affects the soil fertility and potable water.
(c) Burning of fossil fuels produce gases such as carbon dioxide that causes global
warming.
Question 2: Why are we looking at alternate sources of energy?
Answer: Fossil fuels which are traditionally used by human beings everywhere as an energy sources are non-renewable sources of energy. These sources of energy are limited and will disappear after some time. They are being consumed at a large rate. Therefore, we should conserve the energy sources. Hence, we should look for alternate sources of energy.
Question 3:How has the traditional use of wind and water energy been modified for our
convenience?
Answer: Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting water from the well. Today windmills are used to generate electricity. In windmills, the kinetic energy of wind is harnessed and converted into electricity. Water energy which was used for transportation before is now a good source to generate electricity. Dams has been constructed on river for generating electricity. Waterfalls energy which was converted to electricity with the help of turbines.
Question 1: What kind of mirror − concave, convex or plain − would be best suited for use in a solar
cooker? Why?
Answer: A solar cooker uses heat of the sunlight to cook and heat food. A mirror is used in order
to reflect and focus sunlight at a point. A concave mirror is used in a solar cooker for this
purpose. The mirror focuses all the incident sunlight at a point. The temperature at that
point increases, thereby cooking and heating the food placed at that point.
Question 2: What are the limitations of the energy that can be obtained from the oceans?
Answer: The forms of energy that can be obtained from the ocean are tidal energy, wave energy,
and ocean thermal energy. There are several limitations in order to harness these
energies.
(i) Tidal energy depends on the relative positioning of the Earth, moon, and the Sun.
(ii) High dams are required to be built to convert tidal energy into electricity.
(iii) Very strong waves are required to obtain electricity from wave energy.
(iv) To harness ocean thermal energy efficiently, the difference in the temperature of
surface water (hot) and the water at depth (cold) must be 20ºC or more.
Question 3: What is geothermal energy?
Answer: Geothermal power plants use heat of the Earth to generate electricity. This heat energy
of the Earth is known as geothermal energy.
When there are geological changes, the molten rocks present in the core of the earth are
pushed to the earth’s crust. This forms regions of hot spot. Steam is generated when the
underground water comes in contact with these hot spots forming hot springs. This
trapped steam is used to generate electricity in the geothermal power plants.
Question 4: What are the advantages of nuclear energy?
Answer: The advantages of nuclear energy are as follows:
(a) Large amount of energy is produced per unit mass.
(b) It does not produce smoke. It is a clean energy.
(c) Fission of one atom of uranium produces 10 million times the energy released by
burning of one atom of carbon.
(d) Fusion of four hydrogen atoms produces huge amount of energy approximately equal
to 27 MeV.
Question 1: Can any source of energy be pollution-free? Why or why not?
Answer: No source of energy can be pollution-free. Every source of energy has some type of pollution. For example, the wastes of nuclear reaction are very dangerous to the environment.
Question 2: Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG?
Why or why not?
Answer: Hydrogengas is cleaner than CNG. CNG contains hydrocarbons. Therefore, it has carbon
contents. Carbon is a form of pollutant present in CNG. On the other hand, hydrogen is
waste-free. The fusion of hydrogen does not produce any waste. Hence, hydrogen is
cleaner than CNG.
Question 1: Name two energy sources that you would consider to be renewable. Give reasons for
your choices.
Answer: Two renewable sources of energy are as follows:
(a) Sun: The energy derived from the Sun is known as solar energy. Solar energy is
produced by the fusion of hydrogen into helium, fusion of helium into other heavy
elements, and so on. A large amount of hydrogen and helium is present in the Sun.
Therefore, solar energy can replenish on its own. The Sun has 5 billion years more to
burn. Hence, solar energy is a renewable source of energy.
(b) Wind: Wind energy is derived from air blowing with high speed. Wind energy is
harnessed by windmills in order to generate electricity. Air blows because of uneven
heating of the Earth. Since the heating of the Earth will continue forever, wind energy
will also be available forever.
Question 2: Give the names of two energy sources that you would consider to be exhaustible. Give
reasons for your choices.
Answer: Two exhaustible energy sources are as follows:
(a) Coal: It is produced from dead remains of plants and animals that remain buried
under the earth’s crust for millions of years. It takes millions of years to produce coal.
Industrialization has increased the demand of coal. However, coal cannot replenish
within a short period of time. Hence, it is a non-renewable or exhaustible source of
energy.
(b) Wood: It is obtained from forests. Deforestation at a faster rate has caused a
reduction in the number of forests on the Earth. It takes hundreds of years to grow a
forest. If deforestation is continued at this rate, then there would be no wood left on the
Earth. Hence, wood is an exhaustible source of energy.
Question 1: 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 solar water heater uses solar energy to heat water. It requires bright and intense
sunlight to function properly. On a cloudy day, the sunlight reflects back in the sky from
the clouds and is unable to reach the ground. Therefore, solar energy is not available for
the solar heater to work properly. Hence, solar water heater does not function on a
cloudy day.
Question 2: Which of the following is not an example of a bio-mass energy source?
(a) wood (b) gobar gas
(c) nuclear energy (d) coal
Answer: (c) Bio-mass is a source of energy that is obtained from plant materials and animal
wastes. Nuclear energy is released during nuclear fission and fusion. In nuclear fission,
uranium atom is bombarded with low-energy neutrons. Hence, uranium atom splits into
two relatively lighter nuclei. This reaction produces huge amount of energy. In nuclear
fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. This
reaction produces tremendous amount of energy. Hence, nuclear energy is not an
example of bio-mass energy source.
Wood is a plant material, gobar gas is formed from animal dung, and coal is a fossil fuel
obtained from the buried remains of plants and animals. Hence, these are bio-mass
products.
Question 3: 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) Bio-mass
Answer: (c) Nuclear energy is released during nuclear fission and fusion. In nuclear fission,
uranium atom is bombarded with low-energy neutrons. Hence, uranium atom splits into
two relatively lighter nuclei. This reaction produces huge amount of energy. In nuclear
fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. The
energy required to fuse the lighter nuclei is provided by fission reactions. This reaction
produces tremendous amount of energy. These reactions can be carried out in the
absence or presence of sunlight. There is no effect of sunlight on these reactions. Hence,
nuclear energy is not ultimately derived from Sun’s energy.
Geothermal energy, wind energy, and bio-mass are all ultimately derived from solar
energy.
Geothermal energy is stored deep inside the earth’s crust in the form of heat energy.
The heating is caused by the absorption of atmospheric and oceanic heat. It is the
sunlight that heats the atmosphere and oceans.
Wind energy is harnessed from the blowing of winds. The uneven heating of the earth’s
surface by the Sun causes wind.
Bio-mass is derived from dead plants and animal wastes. Chemical changes occur in
these dead plants and animal wastes in the presence of water and sunlight. Hence, bio-
mass is indirectly related to sunlight.
Question 4: Compare and contrast fossil fuels and the Sun as direct sources of energy.
Answer: Fossil fuels are energy sources, such as coal and petroleum, obtained from underneath
the Earth’s crust. They are directly available to human beings for use. Hence, fossil fuels
are the direct source of energy. These are limited in amount. These are non-renewable
sources of energy because these cannot be replenished in nature. Fossil fuels take
millions of years for their formation. If the present fossil fuel of the Earth gets
exhausted, its formation will take several years. Fossil fuels are also very costly.
On the other hand, solar energy is a renewable and direct source of energy. The Sun has
been shining for several years and will do so for the next five billion years. Solar energy
is available free of cost to all in unlimited amount. It replenishes in the Sun itself.
Question 5: Compare and contrast bio-mass and hydro electricity as sources of energy.
uranium atom is bombarded with low-energy neutrons. Hence, uranium atom splits into
two relatively lighter nuclei. This reaction produces huge amount of energy. In nuclear
fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. The
energy required to fuse the lighter nuclei is provided by fission reactions. This reaction
produces tremendous amount of energy. These reactions can be carried out in the
absence or presence of sunlight. There is no effect of sunlight on these reactions. Hence,
nuclear energy is not ultimately derived from Sun’s energy.
Geothermal energy, wind energy, and bio-mass are all ultimately derived from solar
energy.
Geothermal energy is stored deep inside the earth’s crust in the form of heat energy.
The heating is caused by the absorption of atmospheric and oceanic heat. It is the
sunlight that heats the atmosphere and oceans.
Wind energy is harnessed from the blowing of winds. The uneven heating of the earth’s
surface by the Sun causes wind.
Bio-mass is derived from dead plants and animal wastes. Chemical changes occur in
these dead plants and animal wastes in the presence of water and sunlight. Hence, bio-
mass is indirectly related to sunlight.
Question 4: Compare and contrast fossil fuels and the Sun as direct sources of energy.
Answer: Fossil fuels are energy sources, such as coal and petroleum, obtained from underneath
the Earth’s crust. They are directly available to human beings for use. Hence, fossil fuels
are the direct source of energy. These are limited in amount. These are non-renewable
sources of energy because these cannot be replenished in nature. Fossil fuels take
millions of years for their formation. If the present fossil fuel of the Earth gets
exhausted, its formation will take several years. Fossil fuels are also very costly.
On the other hand, solar energy is a renewable and direct source of energy. The Sun has
been shining for several years and will do so for the next five billion years. Solar energy
is available free of cost to all in unlimited amount. It replenishes in the Sun itself.
Question 5: Compare and contrast bio-mass and hydro electricity as sources of energy.
Answer: Bio-mass and hydro-electricity both are renewable sources of energy. Bio-mass is
derived from dead plants and animal wastes. Hence, it is naturally replenished. It is the
result of natural processes. Wood, gobar gas, etc. are some of the examples of bio-
mass.
Hydro-electricity, on the other hand, is obtained from the potential energy stored in
water at a height. Energy from it can be produced again and again. It is harnessed from
water and obtained from mechanical processes.
Question 6: What are the limitations of extracting energy from −
(a) the wind? (b) waves? (c) tides?
Answer: (a) Wind energy is harnessed by windmills. One of the limitations of extracting energy
from wind is that a windmill requires wind of speed more than 15 km/h to generate
electricity. Also, a large number of windmills are required, which covers a huge area.
(b) Very strong ocean waves are required in order to extract energy from waves.
(c) Very high tides are required in order to extract energy from tides. Also, occurrence of
tides depends on the relative positions of the Sun, moon, and the Earth.
Question 7: 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) The source of energy that replenishes in nature is known as renewable source of
energy. Sun, wind, moving water, bio-mass, etc. are some of the examples of renewable
sources of energy.
The source of energy that does not replenish in nature is known as non-renewable
source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non-
renewable sources of energy.
(b) Exhaustible sources are those sources of energy, which will deplete and exhaust after
a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.
derived from dead plants and animal wastes. Hence, it is naturally replenished. It is the
result of natural processes. Wood, gobar gas, etc. are some of the examples of bio-
mass.
Hydro-electricity, on the other hand, is obtained from the potential energy stored in
water at a height. Energy from it can be produced again and again. It is harnessed from
water and obtained from mechanical processes.
Question 6: What are the limitations of extracting energy from −
(a) the wind? (b) waves? (c) tides?
Answer: (a) Wind energy is harnessed by windmills. One of the limitations of extracting energy
from wind is that a windmill requires wind of speed more than 15 km/h to generate
electricity. Also, a large number of windmills are required, which covers a huge area.
(b) Very strong ocean waves are required in order to extract energy from waves.
(c) Very high tides are required in order to extract energy from tides. Also, occurrence of
tides depends on the relative positions of the Sun, moon, and the Earth.
Question 7: 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) The source of energy that replenishes in nature is known as renewable source of
energy. Sun, wind, moving water, bio-mass, etc. are some of the examples of renewable
sources of energy.
The source of energy that does not replenish in nature is known as non-renewable
source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non-
renewable sources of energy.
(b) Exhaustible sources are those sources of energy, which will deplete and exhaust after
a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.
Inexhaustible resources of energy are those sources, which will not exhaust in future.
These are unlimited. Bio-mass is one of the inexhaustible sources of energy.
Yes. The options given in (a) and (b) are the same.
Question 8: What are the qualities of an ideal source of energy?
Answer: An ideal source of energy must be:
I. Economical
II. Easily accessible
III. Smoke/pollution free
IV. Easy to store and transport
V. Able to produce huge amount of heat and energy on burning
Question 9: What are the advantages and disadvantages of using a solar cooker? Are there places
where solar cookers would have limited utility?
Answer: Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean
renewable source of energy. It is free for all and available in unlimited amount. Hence,
operating a solar cooker is not expensive.
Disadvantage of a solar cooker is that it is very expensive. It does not work without
sunlight. Hence, on cloudy day, it becomes useless.
The places where the days are too short or places with cloud covers round the year,
have limited utility for solar cooker.
Question 10: What are the environmental consequences of the increasing demand for energy? What
steps would you suggest to reduce energy consumption?
Answer: Industrialization increases the demand for energy. Fossil fuels are easily accessible
sources of energy that fullfil this demand. The increased use of fossil fuels has a harsh
effect on the environment. Too much exploitation of fossil fuels increases the level of
green house gas content in the atmosphere, resulting in global warming and a rise in the
sea level. It is not possible to completely reduce the consumption of fossil fuels. However, some
measures can be taken such as using electrical appliances wisely and not wasting
electricity. Unnecessary usage of water should be avoided. Public transport system with
mass transit must be adopted on a large scale. These small steps may help in reducing
the consumption of natural resources and conserving them.
These are unlimited. Bio-mass is one of the inexhaustible sources of energy.
Yes. The options given in (a) and (b) are the same.
Question 8: What are the qualities of an ideal source of energy?
Answer: An ideal source of energy must be:
I. Economical
II. Easily accessible
III. Smoke/pollution free
IV. Easy to store and transport
V. Able to produce huge amount of heat and energy on burning
Question 9: What are the advantages and disadvantages of using a solar cooker? Are there places
where solar cookers would have limited utility?
Answer: Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean
renewable source of energy. It is free for all and available in unlimited amount. Hence,
operating a solar cooker is not expensive.
Disadvantage of a solar cooker is that it is very expensive. It does not work without
sunlight. Hence, on cloudy day, it becomes useless.
The places where the days are too short or places with cloud covers round the year,
have limited utility for solar cooker.
Question 10: What are the environmental consequences of the increasing demand for energy? What
steps would you suggest to reduce energy consumption?
Answer: Industrialization increases the demand for energy. Fossil fuels are easily accessible
sources of energy that fullfil this demand. The increased use of fossil fuels has a harsh
effect on the environment. Too much exploitation of fossil fuels increases the level of
green house gas content in the atmosphere, resulting in global warming and a rise in the
sea level. It is not possible to completely reduce the consumption of fossil fuels. However, some
measures can be taken such as using electrical appliances wisely and not wasting
electricity. Unnecessary usage of water should be avoided. Public transport system with
mass transit must be adopted on a large scale. These small steps may help in reducing
the consumption of natural resources and conserving them.
