NCERT Class X Science Solutions: Chapter 14 – Sources of Energy Part 1

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Question 1:

A solar water heater cannot be used to get hot water on

  1. A sunny day.

  2. A cloudy day.

  3. A hot day.

  4. A windy day.


B. A solar water heater uses solar energy to heat water. It requires day light (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.

Hence, the option (B) is correct.

This image shows solar water heater

Solar Water Heater

Question 2:

Which of the following is not an example of a bio-mass energy source?

  1. Wood

  2. Gobar gas

  3. Nuclear energy

  4. Coal


Bio-mass is a source of energy that is obtained from biodegradable natural things (plant materials and animal wastes). Nuclear energy is released during nuclear reactions like fission or fusion producing huge 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.

Hence, the option (C) is correct.

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?

  1. Geothermal energy

  2. Wind energy

  3. Nuclear energy

  4. Bio-mass.


Nuclear energy is released during nuclear fission or fusion. These reactions produces tremendous amount of energy. The energy released during these reaction comes from the mass of elements (mass converts into energy). There is no roll 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.

Hence, the option (C) is correct.

Question 4:

Compare and contrast fossil fuels and the Sun as direct sources of energy.


  • 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 hydroelectricity as sources of energy.


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 (Making dams). Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.

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