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NCERT Science Class 10 Chapter 14 Solutions

Chapter 14: Sources of Energy

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

Ans. 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, a fusion of helium into other heavy elements, and so on. The Sun has enough fuel to for another five billions of years. Thus it is practically inexhaustible.

Hence, solar energy is a renewable source of energy.

(b) Wind: Wind energy is derived from the air blowing with high speed. Wind energy is harnessed by windmills in order to generate electricity. The wind blows because of uneven heating of the Earth surface. Since the heating of the Earth will continue forever, wind energy is also practically inexhaustible.

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

Ans. 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. The industrialization has increased the demand for coal. However, once exhausted, 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.

Q.15. 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) 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, the solar water heater does not function on a cloudy day.

Q.16. Which of the following is not an example of a bio-mass energy source?

(a) wood (b) gobar gas

(c) nuclear energy (d) coal

Ans. (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, the uranium atom splits into two relatively lighter nuclei. This reaction produces a huge amount of energy. In a nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nucleus. This reaction produces a tremendous amount of energy. Hence, nuclear energy is not an example of a biomass 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.

Q.17. 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

Ans. (c) Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atom is bombarded with low-energy neutrons. Hence, the uranium atom splits into two relatively lighter nuclei. This reaction produces a huge amount of energy. In a nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nucleus. The energy required to fuse the lighter nuclei is provided by fission reactions. This reaction produces a 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 time of the planet formation when the other crust gradually cooled and solidified whereas the inner core is still hot and molten. 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, bio-mass is indirectly related to sunlight.

Q.18. Compare and contrast fossil fuels and the Sun as direct sources of energy.

Ans. 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 a direct source of energy. These are limited in amount. These are non-renewable sources of energy because these cannot be replenished within a reasonable time period. Fossil fuels take millions of years for their formation. If the present reserve of fossil fuel of the Earth gets exhausted, its formation will take several years. 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. It replenishes in the Sun itself.

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