Chapter 14 Sources of Energy

Question 1
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
Answer:
(b) A cloudy day.

Question 2
Which of the following is not an example of a biomass energy source ?
(a) Wood
(b) Gobar gas
(c) Nuclear energy
(d) Coal
Answer:
(c) Nuclear energy.

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 ?
(a) Geothermal energy
(b) Wind energy
(c) Nuclear energy
(d) Biomass
Answer:
(a) Geothermal energy.

Question 4
Compare and contrast fossil fuels and the sun as direct sources of energy
Answer:

Fossil fuels	Sun
(i) Non-renewable source of energy.	(i) Renewable source of energy.
(ii) Cause a lot of air pollution.	(ii) Pollution-free, doesn’t cause any pollution.
(iii) They will exhaust in future.	(iii) It is a non-exhaustible source.
(iv) Energy can be tapped throughout the year.	(iv) Energy cannot be tapped during night and cloudy and rainy days.

Question 5
Compare and contrast biomass and hydro-electricity as sources of energy.
Answer:

Biomass	Hydroelectricity
(i) Renewable source of energy.	(i) Renewable source of energy.
(ii) Biomass plants can be installed at any place to produce biomass as energy source.	(ii) Plants can be installed only at the places where dams can be constructed.
(iii) To collect waste materials is a tough and costly process.	(iii) Once the plants start to work, it is not difficult to collect water.

Question 6
What are the limitations of extracting energy from
(a) the wind ?
(b) waves ?
(c) tides ?
Answer:
(a) Limitations of wind energy
(i) Wind energy farms cannot be established everywhere. The wind energy farms can be established only at those places, where wind blows for most part of the year.
(ii) The wind required for generating electricity should be strong and steady to maintain the desired level of generation. The minimum wind speed necessary for satisfactory working of the wind generator is about 15 km/h. This is not always so.
(iii) The wind energy farms require a large area of land.
(iv) The setting up of wind energy farms is very expensive.

(b) Limitations of wave energy : The harnessing of sea-waves energy would be a viable proposition only at those places where sea-waves are very strong. This has constraints of time and location.

(c) Limitations of tidal energy :
(i) There are very few sites around the world which are suitable for building tidal dams.
(ii) The rise and fall of sea-water during high and low tides is not enough to generate electricity on a large scale.

Question 7
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 ?
Answer:
(a) Renewable sources : The sources of energy which are being produced continuously in nature and are inexhaustible, are called renewable sources of energy. The energy derived from flowing water, wind, tides, ocean waves, or wood are examples of energy from such sources.
Non-renewable sources : These sources are produced over million of years under special conditions. Once consumed, these are not replaceable for a very long time. Fossil fuels like coal, petroleum and natural gas are non-renewable sources.
(b) Exhaustible sources are non-renewable sources, while inexhaustible sources are renewable sources.
Yes, the options given in (a) and (b) are the same.

Question 8
What are qualities of an ideal source of energy ?
Answer:
An ideal source of energy

• Must give an adequate amount of net energy.
• Must be convenient to use so as to give energy at a steady rate.
• Must be easy to store and transport.

Question 9
What are the advantages and disadvantages of using a solar cooker ? Are there places where solar cookers would have limited utility ?
Answer:
Advantages of using solar cooker :

1.     The use of solar cooker for cooking food saves precious fuels like coal, kerosene and LPG.

2.     The use of solar cooker does not produce smoke due to which it does not pollute air.

3.     When food is cooked in solar cooker, its nutrients do not get destroyed. This is because in a solar cooker, food is cooked at a comparatively lower temperature.

4.     In a solar cooker, up to four food items can be cooked at the same time.

Disadvantages of using solar cooker :

1.     The solar cooker cannot be used to cook food during night because sunshine is not available at that time.

2.     If the day sky is covered with clouds, even then solar cooker cannot be used to cook food.

3.     The direction of reflector of solar cooker has to be changed from time-to-time to keep it facing the sun.
Sources of Energy

4.     The box-type solar cooker cannot be used for baking (making chappattis, etc.) or for frying.
The places that receive rain most of the year or where the sky remains cloudy, the solar cooker has limited utility.

Question 10
What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption ?
Answer:
Some of the environmental consequences of the increasing demand for energy are the following :

1.     The combustion of fossil fuels is producing acid rain and damaging plants (crops), soil and aquatic life.

2.     The burning of fossil fuels is increasing the amount of greenhouse gas carbon-dioxide in the atmosphere. It has also affected the rainfall.

3.     The cutting down of trees from the forest for obtaining fire-wood is causing soil erosion and destroying wild life.

4.     The construction of hydro-power plants is disturbing ecological balance.

5.     Nuclear power plants are increasing radioactivity in the environment.

 

 

 

The following steps can be taken to reduce energy consumption :

1.     Switch off lights, fans, TV. and other such electrical appliances when not needed, to save electricity.

2.     Use energy efficient electrical appliances to save electricity. This can be done by using compact fluorescent lamps (CFL) and tube lights in place of conventional filament- type electric bulbs.

3.     Good quality stoves should be used to burn fuels like kerosene and LPG so as to obtain maximum heat.

4.     Pressure cookers should be used for cooking food to save fuel.

5.     Solar cookers should be used to cook food whenever possible and solar water heaters should be used to get hot water.

6.     The use of biogas as fuel should be encouraged in rural areas.

7.     Bicycles should be used for short distances to save fuel like petrol which is used in cars, scooters and motorcycles.