NCERT Solutions for Class 10 Science chapter-14 Sources of Energy
1. What is a good
source of energy?
Solution : A good source of energy should have the
following qualities:
(a) It should be
easily available.
(b) It should have
high calorific value.
(c) It should be easy
to store and transport
(d) It should be
economical
(e) It should not
cause environmental pollution
2. What is a good
fuel?
Solution : A good fuel is that which release more
heat on burning, is easily available at the economical rate and do not cause
environmental pollution.
3. If you could use
any source of energy for heating your food, which one would you use and why?
Solution : We shall use LPG/PNG gas or electricity
for heating your food because these are pollution free and have high calorific
value.
4. What are the disadvantages
of fossil fuels?
Solution : There are following disadvantage of
fossil fuels:
(a) Burning of fossil
fuels causes’ pollution.
(b) Oxides of Sulphur
and nitrogen produced on burning of fossil fuel causes acid rain.
(c) Carbon dioxide
causes greenhouse effect.
(d) Fossil fuels are
non-renewable sources of energy.
5. Why are we looking
at alternate sources of energy?
Solution : Fossil fuels are non-renewable sources
of energy and their reserves are limited one. Hence, we need to conserve them.
If we continue consuming these sources at same rate as presently, we may soon
run out of energy. To avoid such a situation, we are looking for alternative
sources of energy.
6. How has the
traditional use of wind and water energy been modified for our convenience?
Solution : Traditionally, waterfalls were used as a
source of potential energy which was converted to electricity with the help of
turbines. Since waterfalls are few in number, water dams have been constructed
in large numbers. Nowadays, hydro-dams are used in order to harness potential
energy of stored water. In water dams, water falls from a height on the
turbine, which produces electricity.
Earlier, the windmills were used to harness wind energy to do mechanical work
such as lifting/drawing water from a well. Today, windmills are used to
generate electricity. In windmills, the kinetic energy of wind is harnessed and
converted into electricity. The rotatory motion of the blades turns the turbine
of the electric generator to generate electricity.
7. What kind of mirror
–concave or convex or plain –would be best suited for use in a solar cooker?
Why?
Solution : 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.
8. What are
limitations of the energy that can be obtained from the oceans?
Solution : Limitations of energy obtained from
oceans:
(a) There are very few
locations where dams to utilize tidal energy can be built.
(b) Cost of
installation of power houses is extremely high and efficiency of plants is comparatively
small.
(c) Power plants built
in oceans will need high continuous maintenance.
9. What is geothermal
energy?
Solution : Geothermal energy is the heat energy
present inside the earth in certain regions called hot spots. When underground
water comes in contact with the hot spot, steam is generated. This steam is
routed through a pipe to a turbine and used to generate electricity.
10. What are the
advantages of nuclear energy?
Solution : Main advantages of nuclear energy are as
follows:
(a) For given mass
fuel consumed the amount of energy released is very large.
(b) Nuclear power
plants can be designed and constructed at any place.
(c) If proper
precautions are taken while running nuclear power plants, a major fraction of
energy need can be obtained from nuclear energy sources.
11. Can any source of
energy be pollution free? Why or why not?
Solution : No, source of energy is completely
pollution free. A source of energy to be pollution free if neither it causes
any pollution during its actual operation nor there any pollution during
assembly of devices utilizing that source of energy. Solar cell device may have
caused some pollution.
12. Hydrogen has been
used as rocket fuel; would you consider it a clear fuel than CNG? Why of why
not?
Solution : Hydrogen can be considered a cleaner
fuel because its burning produces water vapour which is non-polluting. However,
due to explosive nature of hydrogen, its storage and transportation is
difficult.
13. Name two energy
sources that you would consider to be renewable. Give reasons for your choices.
Solution : Solar energy, wind energy, ocean energy
etc. are renewable sources of energy due to the following reasons:
(a) These forms of
energy are available in plenty in our natural environment.
(b) These energy
sources will not be depleted because their supply is large and extraction of
usable energy from these sources is negligible.
14. Give the names of
two energy sources that you would consider to be exhaustible. Give reasons for
your choices.
Solution : Coal and petroleum are two exhaustible
sources of energy. These fuels were formed over million for years ago and there
are only limited reserves. If we continue to use them as at present, these
reserves will be exhausted soon.
15. 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.
Solution : (b) cloudy day.
16. Which of the
following is not an example of a bio-mass energy?
(a) wood
(b) gobar-gas
(c) nuclear energy
(d) coal
Solution : (c) nuclear energy
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?
(a) geothermal energy
(b) wind energy
(c) nuclear energy
(d) bio-mass
Solution : (c) nuclear energy
18. Compare and
contrast fossils fuels and the Sun as direct sources of energy.
Solution : Distinction between fossils fuels and
Sun energy:
19. Compare and
contrast bio-mass and hydro electricity as sources of energy.
Solution : Difference between bio-mass and
hydroelectricity:
20. What are the
limitations of extracting energy from :
(a) the wind?
(b) waves?
(c) tides?
Solution :
Limitation of extracting energy from the wind :
i. It can be
established at those places only, where wind blows for the greater part of a
year.
ii. Wind speed should
be higher than 15 km/h.
iii. It requires high
level of maintenance.
Limitation of extracting
wave energy and tidal energy :
i. It can be harnessed
by trapping the sea waves in a dam. Only very few suitable sites exist where
dams can be constructed.
ii. It is not a
continuous and reliable source of energy.
iii. it is extremely
costly and difficult to use.
21. 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?
Solution :
(a) Renewable sources of energy are those sources which can be regenerated
again. Non-renewable sources of energy are those sources which would get
depleted some day and cannot be regenerated.
(b) Exhaustible
sources of energy are those which will be exhausted some day and cannot be
regenerated. Inexhaustible sources of energy are those which can be regenerated
again due to some continuing or repetitive currents of energy and are
inexhaustible.
Options in both cases
are exactly same.
22. What are the
qualities of an ideal source of energy?
Solution : The qualities of ideal sources of energy
are:
(a) It should be
easily accessible, inexhaustible and a renewable source of energy and cost of
harnessing energy should be reasonably small.
(b) It should be
easily stored and transported.
(c) It should have
high calorific value.
(d) It should be
pollution free.
23. What are the
advantages and disadvantages of using a solar cooker? Are there places where
solar cookers would have limited utility?
Solution :
Advantage of solar cooker :
a. There is no cost of
fuel.
b. It is environment
friendly and there is no residue like ash etc.
c. Cooking is hygienic
and nutritious.
Disadvantage of solar
cooker :
a. The cooking is
slow.
b. It cannot be used
at all times.
c. A solar cooker can
perform only limited functions.
24. What are the
environmental consequences of the increasing demand for energy? What steps
would you suggest to reduce energy consumption?
Solution : The increasing demand for energy is
largely being met by the use of fossil fuels. But these fuels are exhaustible
and non-renewable sources of energy. Moreover, burning of fossils fuels cause
air pollution. Release of acidic oxides leading to acid rain that affect our
water and soil resources. These gases also produce greenhouse effect leading to
increase the temperature of earth.
To reduce energy consumption we should lead a simple and a natural life. As an
example, instead of using an air conditioner in a closed room we should live in
an airy room having appropriate number of windows.
Either way the teacher or student will get the solution to the problem within 24 hours.