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)
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
3) Most of the sources of energy we use represent
stored solar energy. Which of the following is not ultimately derived from the
s energy?
(a) Geothermal energy
(b) Wind energy
(c) Nuclear energy
(d) Bio-mass
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
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 new able 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.
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.
6) What are the limitations of extracting energy
(a) the wind? (b) Waves? (c) Tides?
(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.
7) On what basis would you classify energy sources
renewable and non-renewable?
(b) Exhaustible and inexhaustible? Are the options given
in (a) and (b) the same?
ANSWER:-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. bare 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.
8) What are the qualities of an ideal source of
ANSWER:-An ideal source
of energy must be:
a. Economical
b. Easily accessible
c. Smoke/pollution free
d. Easy to store and
e. Able to produce huge
amount of heat and energy on burning
9) What are the advantages and disadvantages of
using a solar cooker? Are there places where solar cookers would have limited
ANSWER:-Solar cooker uses Suns
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.
10) What are the environmental consequences of the
increasing demand for energy? What steps would you suggest to reduce energy
ANSWER:-Industrialization increases the demand for
energy. Fossil fuels are easily accessible sources of energy that fulfill 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.