Short Answer Type Questions

1 Why is there a need to harness non-conventional sources of energy? Give two main reasons.
Answer. There is a need to harness non-conventional sources of energy because:
(i) fossil fuels are limited sources and are depleting fast.
(ii) burning of fossil fuels causes a lot of pollution.

2. Write two different ways of harnessing energy from ocean.
Answer. Ocean thermal energy and tidal energy can be harnessed from ocean.

Long Answer Type Questions

3. What are the environmental consequences of using fossil fuels? Suggest the steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.
Answer. Environmental consequences of using fossil fuels are:
(i) They are the largest emitters of greenhouse gases such as carbon dioxide and methane.
(ii) Extraction of conventional fuels threatens the ecological balance in many
areas.
(iii) These fuels cause environmental problems due to pollution.
Steps to minimize the pollution are:
(i) The dependency on fossil fuels should be reduced by switching to alternate sources of energy.
(ii) The judicious use of energy by avoiding wastage can reduce environmental problems. –
(iii) Regular servicing of energy conversion devices should be done in order to maintain their efficiency.
(iv) We should focus on developing technology that could make the energy conversion devices much more efficient and cleaner.
(v) Research should be continued to produce long lasting devices so that the environmental damage caused by assembly of devices gets minimized.

4.Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
Answer.Yes, sun is the ultimate source of energy. Directly or indirectly, all the forms of energy are derived from solar energy. Fossil fuels like coal, petroleum and natural gas are formed due to burial of large plants and ancient creatures whose ultimate source of energy is sun. They are indirectly derived from solar energy  such as
(i) – Clouds are formed when water in lakes, rivers, seas etc. evaporates due to solar energy. They bring rainfall and snowfall. The rain and melting snow feed rivers, streams etc. This flowing water can be used for getting hydroelectricity.
(ii) – Wind energy arises due to uneven heating of the earth’s surface by the sun rays at two different adjoining places. Due to this, wind possesses kinetic energy.
(iii) – Plants in the process of photosynthesis converts the solar
energy into food (chemical energy). This food is consumed by animals. Thus, the animal wastes and remains of the plants constitute biomass which can be utilised as a source of energy.
(iv) – The waves are generated by strong winds (due to solar energy) blowing across the sea.
(v) – Sun is responsible for the temperature difference between the water at the surface and water at depth in seas and oceans.
Thus the energy from various sources is considered to have been derived from
the sun.