Chapter 14 Sources of Energy

In Text Questions

Question 1.
What is good source of energy ?
A substance which produces sufficient amount of energy over a long period of time without producing much smoke is known as good source of energy. Characteristics of a good source of energy.

Question 2.
What is good fuel ?
What is a fuel ?
A fuel which provides large amount of heat energy without causing pollution.

Question 3.
If you could use any source of energy for heating your food, which one would you use and why ?
We would use microwave oven for heating our food. This is because the nutritional value of food is not lost when heated in a microwave oven.

Question 4.
What are the disadvantages of fossil fuels ? (CBSE 2010)

  1. They cause environmental pollution.
  2. They cause global warming.
  3. They do not supply enough heat energy.
  4. The by-products of burning fuels cause acid rain which pollute water resources.

Question 5.
Why are we looking at alternate sources of energy ?
State one reason that has necessitated to look for alternate sources of energy ? (CBSE 2013)
Because the conventional sources of energy may completely be exhausted one day if their use at the present rate continues.

Question 6.
How has the traditional use of wind energy and water been modified for our convenience
(CBSE 2010, Term I)
These energies have been converted into electrical energy using electric generators.

Question 7.
What kind of mirror—concave, convex or plane would be best suited for the use in a solar cooker. Why ?
Concave mirror, because it focusses the sun rays at a point to raise the temperature at that point.

Question 8.
What are the limitations of the energy that can be obtained from oceans ? (CBSE 2010)
List any four limitations of the energy obtained from oceans. [CBSE (All India) 2009, 2012]

  1. Energy from oceans is available only when high tides are in the ocean.
  2. Power plants used to convert ocean energy into electric energy do not operate continuously.
  3. Energy of ocean waves can be extracted blow all times across the ocean.
  4. Tidal power plants can not be installed everywhere.

Question 9.
What is geothermal energy ? (CBSE 2010, Term I, 2011, 2012)
The heat energy stored in the hot spots of the earth’s crust is called geothermal energy.

Question 10.
What are the advantages of nuclear energy ?

  1. A small quantity of nuclear fuel gives a large amount of energy.
  2. In a nuclear power plant, the nuclear fuel is inserted once to get energy over a longer period of time.

Question 11.
Can any source of energy be pollution free ? Why or why not ?
No source of energy is there which is pollution free. However, some sources of energy cause more pollution and some sources of energy cause less pollution.

Question 12.
Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not ?
Hydrogen causes less air pollution than C.N.G. because burning of hydrogen produces water vapours and burning of CNG produces CO2. When the concentration of CO2 increases in the atmosphere, then the temperature of the atmosphere increases. This effect is known as green house effect. The increased temperature of the atmosphere affects life on the earth.

Question 13.
Name two energy sources that you would consider to be renewable. Give reasons for your choices.

  1. Bio-mass is considered as a renewable source of energy because forests can be replenished.
  2. Water is also a renewable source of energy as water is continuously available to use due to water cycle in nature.

Question 14.
Give the names of two energy sources that you would consider to be exhaustible.
Give reasons for your choices,

  1. Coal
  2. Petroleum.

They will be exhaustible when continuously extracted. Moreover, the formation of these fuels under the earth takes a longer period of time.

NCERT Chapter End Exercises

Question 1.
A solar 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.

Question 2.
Which of the following is not a example of a bio-mass energy source ?
(a) wood,
(b) gobar gas,
(c) fossil fuels,
(d) bio-mass. (Bihar Board 2012)

Question 3.
Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Suns energy ?
(a) geothermal energy,
(b) wind energy,
(c) fossil fuels,
(d) bio-mass.

Question 4.
Compare and contrast fossil fuels and the Sun as a source of energy.

  1. Energy of fossil fuels comes from the solar energy. However, fossils fuels are the non-renewable sources of energy. On the other hand, sun is a renewable source of energy.
  2. Fossil fuels cause pollution but solar energy does not cause pollution.
  3. Energy is supplied by fossil fuels at any time of the day but sun supplies energy only when it shines.

Question 5.
Compare and contrast bio-mass and hydro-electricity as source of energy.


Hydro electricity

(i)    The energy supplied by the burning of bio-mass causes pollution.

(ii)    The energy from bio-mass can be obtained by burning it directly or by a gobar gas plant.

(i)     Hydro-electricity does not cause pollution.

(ii)    Hydro-electricity can be obtained by constructing costly dams.

Question 6.
What are the limitations of extracting energy from
(a) the wind
(b) Waves
(c) Tides ?

  1. We cannot depend upon wind energy as it is available only when strong wind blows. The appliances or machines operating with wind energy stop working as soon as wind stops. The minimum speed of wind to operate generator to produce electricity is 15 km/h.
  2. Wind energy is not sufficient to operate heavy machines.
  3. The use of wind energy is limited to certain places where strong winds blow most of the time.

(b) Energy of waves can be extracted only if strong winds blow all the time across the sea.
(c) Tidal power plant can extract energy from the waves only when the difference between the water levels of high tide and low tide is very large.

Question 7.
On what basis you classify energy source as
(a) Renewable and non-renewable ?
(b) Exhaustible and inexhaustible ?
(c) Are the options given in (a) and (b) the same ?
(a) Renewable Sources of Energy are those which are continuously supplied by nature. For example, the sun, the wind.
(b) Non-Renewable Sources of Energy are those which have been formed in nature long ago under certain conditions of temperature and pressure. Non-renewable sources of energy take longer period of time for their formation. For example, fossil fuels like coal, petroleum.
(c) Inexhaustible Sources of Energy are those which supply continuous energy for unlimited time. In fact, exhaustible sources of energy are also termed as non-renewable energy sources. But wood is an exception as it can be made renewable by growing more plants periodically. Inexhaustible sources of energy are termed as renewable sources of energy.

Question 8.
What are qualities of an ideal source of energy ?
Write any two characteristics of a good source of energy. (CBSE 2013)

  1. It supplies useful energy continuously.
  2. It does not cause environment pollution.
  3. It is economical.

Question 9.
What are the advantages and disadvantages of using a solar cooker ? Are there places where solar cookers would have limited utility ? (CBSE 2010)

  1. There is no cost of cooking food in a solar cooker.
  2. No pollution is caused when food is cooked in a solar cooker.
  3. Nutrition value of food is preserved when food is cooked in the solar cooker.
  4. Two or three dishes can be cooked at a time.


  1. Food cannot be cooked at night and on a cloudy day using a solar cooker.
  2. The cost of making solar cooker is high.
  3. Food cannot be cooked quickly with the solar cooker.
  4. Large quantity of food cannot be cooked with a solar cooker.
  5. Chapatis cannot be made with solar cooker.
    Solar cooker will have limited utility at places where the sun shines for shorter period of time or where the sun rays never reach.

Question 10.
What are the environmental consequences of the increasing demand for energy ? What steps would you suggest to reduce energy consumption ?

  1. More use of fossil fuels for fulfilling the increasing demand for energy is polluting air (i.e. the environment),
  2. LPG and CNG are considered as clean fuels but the extraction and transportation of these fuels cause environmental pollution.
  3. The use of large number of sources of energy is causing global warming.


  1. Burning fuels must be extinguished as soon as their use is over.
  2. Bulbs, tubes and other electrical appliances must be switched off as soon as you leave your room.
  3. The engines of the vehicles must be switched off when these vehicles are stopped for more than a minute to save fuel.