Chapter 1

Sources of energy

NCERT in-text questions

Page no 243 

1) What is a good source of energy? Or list any three parameterson the basis of which a source of energy can be categorized as a good source of energy.
Ans: A source of energy can be called a good source of energy if :

  • It provides a large amount of work per unit volume or mass
  • It is cheap and can be easily accessible.
  • It should be economic and has a high calorific value.
  • It is easy to store and transportable.
  • It does not cause any environmental pollution.
2) What is a good fuel?
Ans: A good fuel should have the following characteristics :
  • A good fuel should be easily available and release a good amount of heat on burning.
  • It should not produce smoke or any harmful gases.
  • It should be safe to handle, store and transport.
  • It should be inexpensive.
  • It should leave any residue after burning.
3) If you could use any source of energy for heating your food, which one would you use, and why? 
Ans: We should use natural gas because it is a clean source of energy. It does not produce smoke on burning. It is easily accessible and easily transportable and produces a large amount of heat on burning. It does not leave behind any residue after burning.
Page no 248 

1) What are the disadvantages of fossil fuels? Ans: The disadvantages of fossil fuels are as follows :
  1. The burning of fossil fuels causes air pollution
  2. They are non-renewablesources of energy
  3. They enhance the greenhouse effect on burning
2) Why are we looking at alternate sources of energy?
Ans: These days, we are using fossil fuels as energy sources. They are non-renewable sources of energy which are limited and cannot replenish on their own. We are consuming fossil fuels at a large rate. If this rate of consumption continues, then the fossil fuels would be exhausted from the earth. Thus, we have to conserve energy sources and that’s why we are looking at alternate sources of energy.

3) How has the traditional use of wind and water energy been modified for our convenience?
Ans:(a) The traditional use of wind energy has been modified to the windmill which is used to generate electricity as well as in water lifting pumps. (b) the traditional use of following water energy has been modified to hydroelectric power plants to generate electricity.

Page number 253 

1) What kind of mirror- concave, convex or plane would be best suited for use in a solar cooker? Why?
Ans: A concave mirror is best suited for use as a reflector in a solar cooker. The concave mirror focuses all the incident sunlight at a point. The temperature at that point increases and the food is cooked.

2) What are the limitations of the energy that can be obtained from the oceans?
Ans: The energies that can be obtained from the oceans are tidal energy, wave energy, ocean thermal energy. The limitations of the energy are :
  • Conversion effect efficiency of ocean thermal energy powerplant is very low
  • High dams are required to build to convert tidal energy into electricity. To construct such dams, only a few locations are available.
  • Very strong waves in the sea are needed to harness electricity from them.
  • Power plant requires high maintenance cost during its operation.
3) What is geothermal energy?
Ans: The heat energy of the interior of the earth is called geothermal energy.

4) What are the advantages of nuclear energy?
Ans: The advantages of nuclear energy are
  • A large amount of energy is produced by unit mass.
  • It does not produce pollution so it is a clean fuel, provided plant is operated properly with almost care.
  • Only a small quantity of nuclear fuel is required to run a nuclear power plant over a long period of time as compared to thermal power plant.
5) Can any source of energy be pollution-free? Why or why not?
Ans: No source of energy is pollution-free. Even if the conversion of energy to the required form is pollution-free, the assembly of the device used would have caused some damage to the environment.

6) Hydrogen has been used as rocket fuel. Would you consider it a cleaner fuel than cng? Why or why not?
Ans: Yes, hydrogen is a cleaner fuel than cng. The rocket carries oxygen which helps in burning the hydrogen. It is used as a fuel and produces water. Water does not cause any damage to the environment.
On the other hand, cng on burning produces carbon dioxide and water. Carbon dioxide is not a pollutant yet it leads to a rise in temperature. This would affect the polar ice and life on the earth is at risk due to global warming.

Page number 254 

1) Name two energy sources that you would consider to be renewable. Give reasons for your choices.
  Mention any two renewable sources of energy.
  • Energy due to the flow of water- due to the continuous water cycle in nature.
  • Wind energy- repetitive current of wind is more or less available at all the places.
2) Give the names of two energy sources that you would consider to be exhaustible. Give reason for your choices
Ans: Coal and petroleum are considered exhaustible sources of energy because millions of years ago, large plants, ancient creators died. They were decomposed and were buried layer upon layer under the earth. Due to high pressure and excess amounts of heat, generated, over millions of years, these layers converted into fossil fuels. Once they are depleted, they cannot be produced quickly in nature. Therefore they are considered as exhaustible sources of energy.

NCERT Exercise 

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
Ans: (b) On a cloudy day, a solar water heater cannot be used as solar energy is not available.

2) Which of the following is not an example of a bio-mass energysources?
    a) Wood
    b) Gober-gas
    c) Nuclear energy
    d) Coal
Ans: ( c ) Nuclear energy is not a source of biomass energy.

3) Most of the sources of energy we use represent stored solar energy. Which of the following is not unlimited derived from the sun’s energy?
    a) Geothermal energy
    b) Wind energy
    c) Nuclear energy
    d) Bio-mass
Ans: (a) Geothermal energy is also not derived from solar energy. It is obtained from the molten rocks in the deeper hot region of the earth.
( c ) Nuclear energy is derived from the nucleus of various atoms.

4) Compare and contrast fossils fuels and the sun as direct sources of energy. Ans: Most of the fossil fuels are formed by solar energy whereas the solar energy is a result of nuclear reactions.
  • Fossil fuels cause pollution, whereas solar energy does not pollute the environment.
  • Fossil fuels are non- renewable sources of energy whereas solar energy is a renewable source of energy.
5) Compare and contrast bio- mass and hydroelectricity as sources of energy.
Ans: -> Products of biomass can be used as manure while in hydroelectricity, no such products are formed.
-> The amount of electricity that can be generated from biomass is far low in comparison to hydroelectric.

6) What are the limitations of extracting energy from :
    (a) the wind
    (b) waves?
    ( c )tides?
Ans: (a)-> Not available at all the time and at all the places.
->Needs a large open field.
(b) -> Affected by wind movement.
-> Not available at all the places
( c ) -> Depends on the faces of the moon
-> Conversion efficiency is less

7) On what basis would you classify the energy sources as
a) Renewable and non-renewable?
b) Exhaustible and inexhaustible?
Are the options given in a and b the same?

Ans: (a) Renewable and Non-Renewable
Whether the energy source is available continuously or not
(b) Exhaustible and inexhaustible If the form of energy is formed as a result of long-time taking processes, then it will be exhaustible, for example coal and petroleum. If it is formed in a short time by a continuous process, it will be inexhaustible.
The options given in a and b  are the same by way of availability.

8) What are the quantities of an ideal source of energy? Ans: characteristics of an ideal source of energy are :
  • Capable of providing an adequate amount of energy
  • Should be convenient to use and easy to store and transport
  • Should be capable of giving the desired quality at the required rate steadily over a long period.
  • Should raise energy in mostly all forms in which the day to day requirement exists.
9) What are the advantages and disadvantages of using a solar cooker? Is there a place where solar cookers would have limited utility?
Ans: Advantages of the solar cooker are
  • It saves fuel.
  • It does not create pollution.
  • The nutrients of food do not get destroyed.
Disadvantages of the solar cooker are 
  • It cannot be used during night time and on a cloudy day.
  • The direction of the reflector of the solar cooker has to be adjusted frequently.
  • It cannot be used for frying and making chapatis.
Yes, there are places where solar cookers would have limited utility like in the polar regions, where there is no sunlight for a large  part of the year and at high altitudes, such as hilly areas where the sun shines for a limited period of time and in a dense forest where the sun rays never reach the surface.

10) What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Ans: Consequences are
  • More pollution levels
  • Quicker depletion of conventional sources
Steps to overcome energy crisis are 
  • Promoting renewable energy sources
  • Promoting efficient convention mechanism
  • Accelerate the pace of development of technologies required for harnessing new sources.