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, gobargas, 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. Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.

(a) A windmill requires wind of speed more than 15 km/h to generate electricity from wind energy also large numbers of windmills are required to get feasible output which covers a large area.

(b) Very strong ocean waves are required in order to extract energy from waves.

(c) Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.

(a) The source of energy that replenishes in nature is known as renewable source of energy. Sun, wind, moving water, bio-mass, etc. are some of the examples of renewable sources of energy.
The source of energy that does not replenish in nature is known as non-renewable source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non-renewable sources of energy.

(b) Exhaustible sources are those sources of energy, which will deplete and exhaust after a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.
Inexhaustible resources of energy are those sources, which will not exhaust in future. These are unlimited. Bio-mass is one of the inexhaustible sources of energy.

Yes. The options given in (a) and (b) are the same.

An ideal source of energy must be:
→ Economical
→ Easily accessible
→ Smoke/pollution free
→ Easy to store and transport
→ Able to produce huge amount of heat and energy on burning

Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean renewable source of energy. It is free for all and available in unlimited amount. Hence, operating a solar cooker is not expensive.
Disadvantage of a solar cooker is that it is very expensive. It does not work without sunlight. Hence, on cloudy day, it becomes useless.
The places where the days are too short or places with cloud covers round the year, have limited utility for solar cooker.

Industrialization increases the demand for energy. Fossil fuels are easily accessible sources of energy that fulfil this demand. The increased use of fossil fuels has a harsh effect on the environment. Too much exploitation of fossil fuels increases the level of green house gas content in the atmosphere, resulting in global warming and a rise in the sea level.
It is not possible to completely reduce the consumption of fossil fuels. However, some measures can be taken such as using electrical appliances wisely and not wasting electricity. Unnecessary usage of water should be avoided. Public transport system with mass transit must be adopted on a large scale. These small steps may help in reducing the consumption of natural resources and conserving them.

1. Which of the following is a non-renewable source of energy?
(a) Wood
(b) Sun
(c) Fossil fuels
(d) Wind
Ans. (c) Fossil fuels

Explanation: It takes millions of Years of the formation of fossil fuels. So, they cannot be renewed in foreseeable future.
2. Acid rain happens because
(a) sun leads to heating of upper layer of atmosphere
(b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere
(c) electrical charges are produced due to friction amongst clouds
(d) earth atmosphere contains acids
Ans. (b) burning of fossil fuels release oxides of carbon, nitrogen and Sulphur in the atmosphere
Explanation: Oxides of carbon, nitrogen and sulphur mix with rain water to form acids. This causes acid rain.

3. Fuel used in thermal power plants is
(a) water
(b) uranium
(c) biomass
(d) fossil fuels
Ans. (d) fossil fuels
Explanation: Coal is the major fuel used in thermal power plants. Additionally, natural gas and petroleum gas are also used.

4. In a hydro power plant
(a) Potential energy possessed by stored water is converted into electricity
(b) Kinetic energy possessed by stored water is converted into potential energy
(c) Electricity is extracted from water
(d) Water is converted into steam to produce electricity
Ans. (a) Potential energy possessed by stored water is converted into electricity
Explanation: Water is stored behind dams. The stored water has potential energy. When water is released from the dam; Potential energy changes into kinetic energy. This kinetic energy is utilized to turn the turbine to generate electricity.

5. Which is the ultimate source of energy?
(a) Water
(b) Sun
(c) Uranium
(d) Fossil fuels
Ans. (b) Sun
Explanation: Fossil fuels were made from biomass and biomass is made because of photosynthesis. We know that solar energy is converted into biomass through photosynthesis. 
Water cycle is driven by sun and hence kinetic energy in water is because of sun. Hence, it is said that sun is the ultimate source of energy.

6. Which one of the following forms of energy leads to least environmental pollution in the process of its harnessing and utilisation?
(a) Nuclear energy
(b) Thermal energy
(c) Solar energy
(d) Geothermal energy
Ans. (c) Solar energy

7. Ocean thermal energy is due to
(a) energy stored by waves in the ocean
(b) temperature difference at different levels in the ocean
(c) pressure difference at different levels in the ocean
(d) tides arising out in the ocean
Ans. (b) temperature difference at different levels in the ocean
Explanation: Energy from warm surface is used to boil a volatile liquid. Vapours of this liquid are utilized to turn the turbine. Then vapours are channelized to deeper oceans so that they can cool down.

8. The major problem in harnessing nuclear energy is how to
(a) split nuclei?
(b) sustain the reaction?
(c) dispose off spent fuel safely?
(d) convert nuclear energy into electrical energy?
Ans. (c) dispose off spent fuel safely?
Explanation: Spent fuel from a nuclear plant contains highly radioactive material. This can be very harmful for living beings and for the environment.

9. Which part of the solar cooker is responsible for green house effect?
(a) Coating with black colour inside the box
(b) Mirror
(c) Glass sheet
(d) Outer cover of the solar cooker
Ans. (c) Glass sheet

10. The main constituent of biogas is
(a) methane
(b) carbon dioxide
(c) hydrogen
(d) hydrogen sulphide
Ans. (a) Methane

11. The power generated in a windmill
(a) is more in rainy season since damp air would mean more air mass hitting the blades
(b) depends on the height of the tower
(c) depends on wind velocity
(d) can be increased by planting tall trees close to the tower 
Ans. (c) depends on wind velocity
Explanation: Higher wind velocity will turn the turbine at higher speed. This will help in more power generation.

12. Choose the correct statement
(a) Sun can be taken as an inexhaustible source of energy
(b) There is infinite storage of fossil fuel inside the earth
(c) Hydro and wind energy plants are non polluting sources of energy
(d) Waste from a nuclear power plant can be easily disposed off
Ans. (a) Sun can be taken as an inexhaustible source of energy

13. In a hydroelectric power plant more electrical power can be generated if water falls from a greater height because
(a) its temperature increases
(b) larger amount of potential energy is converted into kinetic energy
(c) the electricity content of water increases with height
(d) more water molecules dissociate into ions
Ans. (b) larger amount of potential energy is converted into kinetic energy

Explanation: Potential energy increases with increase in height.

14. Choose the incorrect statement regarding wind power
(a) It is expected to harness wind power to minimum in open space
(b) The potential energy content of wind blowing at high altitudes is the source of wind power
(c) Wind hitting at the blades of a windmill causes them to rotate the rotation thus achieved can be utilised further
(d) One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator
Ans. (b) The potential energy content of wind blowing at high altitudes is the source of wind power
Explanation: A windmill works on kinetic energy of wind.

15. Choose the incorrect statement
(a) We are encouraged to plant more trees so as to ensure clean environment and also provide bio-mass fuel
(b) Gobar-gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen
(c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash
(d) Bio-mass is a renewable source of energy
Ans. (c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash
Explanation: The main ingredient of biogas is methane. It burns without smoke and leaves no residue.