Chapter 14 Sources of Energy
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 have been
traditionally used by human beings as an energy sources, are non-renewable
sources of energy. These sources of energy are limited and cannot replenish on
their own. They are being consumed at a large rate. If this rate of consumption
continues, then the fossil fuels would be exhausted from the Earth. Therefore,
we have to 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:
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.
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.
Can any source of energy be pollution-free? Why or why not?
Answer:
No source of energy can be
pollution-free. It is considered that solar cells are pollutionfree. However,
even their making causes environmental damage indirectly.
Also, in the case of nuclear
energy, there is no waste produced after the fusion reactions. However, it is
not totally pollution-free. To start the fusion reactions, approximately 107
K temperature is required, which is provided by fission reactions. The wastes
released from fission reactions are very hazardous. Hence, no source of energy
is pollution-free.
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.
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.
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, biomass 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 biomass.
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 nonrenewable 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 fulfil 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.
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