Q1. 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

Solution: b) A sunny day

Q2. 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) Nuclear energy

Q3. 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

Q4. Compare and contrast fossil fuels and the sun as direct sources of energy.

(i) The fossil fuels are limited i.e, exhaustible whereas solar energy in available in abundance i.e. inexhaustible.
(ii) When we burn fossil fuels it causes pollution whereas solar is pollution free.
(iii) Fossil fuels can provide energy at any required time whereas solar energy becomes unavailable when the sky is covered with clouds.

Q5. Compare and contrast bio-mass and hydroelectricity as sources of energy.

(i) Biomass may be considered as a renewable source of energy only if we plant tree in a planned manner but hydroelectricity may also a renewable source if the water is available.
(ii) Biomass energy can be obtained from wood, dung etc. by using chullah or gobar gas plant whereas hydroelectricity obtained from water by constructing dams on rivers.
(iii) If we burnt firewood it causes pollution or if we produce bio-gas it is a pollution-free source of energy but hydroelectricity is a pollution-free source of energy.

Q6. What are the limitations of extracting energy from:
a. The wind?
b. Waves?
c. Tides?

a) The wind: Wind energy is trapped using windmills. One of the limitations of the wind energy is that windmills require a speed more than 15 km/h to generate electricity. And the number of windmills will be more to cover a huge area.
b) Waves: In order to extract energy from the waves, very strong ocean waves are needed.
c) Tides: In order to extract energy from the tides, the sun, the moon and the earth should be in straight alignment and the tides should be very strong.

Q7. On what basis would you classify energy sources as:
a. Renewable and non-renewable?
b. Exhaustible and inexhaustible?

Are the options given in (a) and (b) the same?

a) Renewable and non-renewable:
Renewable energy sources are those which replenish on their own and are easily available in nature. Like solar energy, tidal energy, wind energy, bio-mass.

Non-renewable energy sources are those which do not replenish on their own and have limited availability in nature. Like fossil fuels which include petroleum, coal, and natural gas.

b) Exhaustible and inexhaustible:

Exhaustible sources of energy are those which deplete after  few hundred years. Like coal and petroleum.

An inexhaustible source of energy are those which do not deplete and are available in abundant quantity. Like solar and wind energy.

Q8. What are the qualities of an ideal source of energy?

Following are the qualities of an ideal source of energy:

i. It should be economical
ii. It should be easily available


i. Easy transportation and storage
ii. The amount of energy produced when burnt should be huge.

Q9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Ans:- Advantages:- The heat source for a solar cooker is sunlight. It is a clean renewable and inexhaustible source of energy. As its availability is unlimited, it will be pocket-friendly.

Disadvantages:- It doesn’t work on a cloudy day.

Q10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Ans:- The following are the environmental consequences of the increasing demand for energy:-
(i) To meet the increasing demand for energy, the burning of fossil fuel and fire woof causes air-pollution.
(ii) To produce hydroelectricity, construction of dams on the river which may change the ecosystem and many plants submerged underwater and release large amounts of methane gas which contribute to the greenhouse effect.

The following steps may reduce energy consumption –
(i) To reduce the consumption of fossil fuel we should have used some alternative sources of energy such as solar energy, biogas, etc.
(ii) Fossil fuel should be used with care and caution to derive maximum benefits from fossil fuel.
(iii) Fuel-saving devices such as pressure cookers etc. should be used.
(iv) Switch off the fans, electric bulb, and other electric appliances where these are not in use.
(v) We should be economical in our energy consumption.


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