Class 10 Science

Sources of Energy

NCERT In Text Question

What is a good fuel?

Answer: A good fuel should have many desirable characteristics. Some of them are as follows:

  • It should produce a high amount of energy for each unit of mass or volume.
  • It should be easily available and should be easy to transport.
  • It should be economical.

What is a good source of energy?

Answer: A good source of energy should be renewable and environment friendly.

If you could use any source of energy for heating your food, which one would you use and why?

Answer: I will use LPG (Liquefied Petroleum Gas) for heating my food, because it is easily available in my kitchen, gives no smoke on burning and takes less time to do the job.

What are the disadvantages of fossil fuels?

Answer: Following are the disadvantages of fossil fuels:

  1. They are non-renewable
  2. They produce air pollutants on burning.
  3. Why are we looking at alternate sources of energy?

    Answer: Because of growing population, the energy demand is rising. Fossil fuels are going to be exhausted in the near future and burning them is causing air pollution. Hence, we need to find an alternate source of energy which is renewable and environment friendly.

    How has the traditional use of wind and water energy been modified for our convenience?

    Answer: Before the beginning of the Industrial revolution, wind and water energy were used for serving many purposes but the ways of their use were not efficient. For example, windmills were used to power smaller mills, like flour mills or saw mills. The flow of water was used for transporting wooden logs. Now-a-days, both wind energy and water energy are being harnessed to produce electricity which means a better and more efficient use of these forms of energy.

    What kind of mirror, concave or convex or plain would be best suited for use in a solar cooker? Why?

    Answer: A concave mirror is best suited for use in a solar cooker. The reason for this is the ability of a concave mirror to converge the solar energy at a point. This enables the concave mirror to produce a larger amount of heat, compared to other types of mirror.

    What are the limitations of the energy that can be obtained from the oceans?

    Answer: Limitations of energy which can be obtained from the oceans:

    • These forms of energy can be harnessed only in coastal areas; which would leave a vast portion of the human habitation.
    • The technologies for harnessing them are still at experimental stage and hence are very costly and less efficient.

    What is geothermal energy?

    Answer: The energy which can be harnessed from the heat of inside of the earth is called geothermal energy.

    What are the advantages of nuclear energy?

    Answer: Advantages of nuclear energy are as follows:

    • A small amount of radioactive material can generate a huge amount of energy.
    • It does not produce air pollution.
    • A nuclear power plant is more efficient than other power plants.

    Can any source of energy be pollution free? Why or why not?

    Answer: Many sources of energy can be pollution free. When burning of biomass is not involved in production of energy, then there is no chance of pollution. For example, wind energy, hydel energy, solar energy, etc. are pollution free.

    Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

    Answer: Hydrogen is a much cleaner energy source than CNG. CNG (compressed natural gas) is derived from biomass and hence burning the CNG causes air pollution, albeit on a much smaller scale than coal and petroleum. Use of hydrogen as energy source does not polluting gases.

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

    Answer: Solar energy and wind energy are examples of renewable energy sources because they get quickly replenished.

    Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choice.

    Answer: Coal and petroleum are exhaustible energy sources because their stock is going to be finished in the near future and it takes millions of years for their formation.

Chemical Reaction

Chemical change is called chemical reaction. A new substance is formed after chemical reaction.

Acid Base Salt

Acids and bases dissociate into ions in aqueous solution. Salt is formed on reaction between acid and base.

Metals Non-metals

Elements are of two types: metals and non-metals which have different chemical and physical properties.

Carbon Compounds

Compounds of carbon are called organic compounds and are millions in number.

Periodic Classification

As per modern periodic classification, properties of elements are periodic function of their atomic number.

Life Processes

Biological processes essential to continue life are called life processes.

Control Coordination

In complex animals, control and coordination of various functions are achieved by nervous system and hormones.


The process by which a living being produces its offspring is called reproduction.

Heredity Evolution

Inheritance of traits from one generation to next is called heredity. All living beings have evolved from a common ancestor.

Light Reflection

Bouncing back of light from a shiny surface is called reflection of light.

Light Refraction

Deviation in path of light when light travels from one medium to another is called refraction of light.

Human Eye

Human eye works like a camera and gives us the sense of vision.


Flow of electric charge is called electric current.


Magnetic field is present around a current carrying conductor, and a magnet in electric field experiences a force due to electric field.

Source of Energy

An ideal source of energy should be ecnoomical, easy to carry, easy to store and should not produce too much waste.


The system of interdependency among living beings and non-living things is called ecosystem.

Natural Resources

We need to judiciously utilise natural resources because they are scarce.