14. SOURCES OF ENERGY
Questions:
1. Name the two major components present in the left-over slurry of a biogas plant.
Ans: Nitrogen and phosphorus.
2. What is a wind energy farm?
Ans: A number of windmills erected over a large area.
3. Write any two advantages of bio-energy. [SSLC April 2016]
Ans: (i) It maintains an unpolluted environment. (ii) Reduces the carbon dioxide content in the atmosphere.
4. Name any two elements that are used in fabricating solar cells.
Ans: Silicon / Gallium / Silver.
5. Define the term-biomass. Name any two biomass energy sources.
Ans: The materials obtained from plants and animals, used as fuels are called biomass. Coal, wood etc., are the sources of biomass energy.
6. What should be the minimum wind speed to maintain the required speed of the turbine in a wind energy farm?
Ans: l5km/h.
7. What are the two disadvantages of burning fossil fuels?
Ans: Disadvantages are air pollution and acid rain which affects soil and water.
8. Mention any one reason due to which most of the thermal power plants are set up near coal or oil fields.
Ans: Because fuel is used to produced heat energy by burning.
9. Write two disadvantages of Nuclear Energy.
Ans: (i) Used for production and proliferation of nuclear weapons. (ii) Its generation is very expensive.
10. Why are black surfaces, and not the white surfaces, used for making solar cookers?
Ans: Black surfaces absorb more heat as compared to white surfaces. Therefore, for making solar cookers, black surfaces are used.
11. What is a nuclear fusion reaction? List any two advantages of nuclear fusion reactions.
Ans: A reaction in which two nuclei of lighter elements combine to form a heavy nucleus with a liberation of tremendous amount of energy is nuclear fusion reaction. Two advantages are:
(i) Large amount of energy is produced from a very small amount of fuel.
(ii)Produces nonpolluting waste/does not produce gases which pollute the environment/cause green house effect.
12. Mention the main use of slurry left behind in the biogas of plant. State the characteristics of the slurry, on which this use is based.
Ans: (i) Slurry is used as a manure. 1 (ii) Slurry is rich in nitrogen and phosphorus.
13. Give two advantages of using nuclear energy.
Ans: Two advantages of using nuclear energy are: (i) Very small mass of Uranium yields tremendous energy.
(ii) The released energy can be used to produce steam and further generate electricity.
14. Name the major constituent of biogas. List three characteristics to prove it as an excellent fuel.
Ans: Methane is the major constituent of biogas. Three characteristics to prove it as an excellent fuel are: (i) Smokeless (ii) Leaves no residue (iii) Higher heat of combustion.
15. Large scale use of nuclear energy becomes prohibitive due to some hazards. State any two major hazards associated with a nuclear power plant.
Ans: (i) Storage and disposal of spent or used fuels which decay into sub-atomic particles with harmful radiations.
(ii) Nuclear waste storage and disposal result in environment contamination or accidental leakage of nuclear radiations.
16. Why does a car parked in sunlight remains hot from inside even when there is no sunlight in the car?
Ans: The glass windows have the peculiar property to pass radiations which have wavelength near to the visible light or shorter wavelength. It does not allow infra-red radiations of higher wavelength. Since the sun sends in fra-red radiations of lower wavelengths, it gets trapped inside the car in the form of heat. This heat or infra-red radiations can not pass out and thus gets trapped in the car for longer time, making it hot from inside.
17. Draw a neat diagram of a biogas plant and label (i) inlet of slurry, (ii) digester and (iii) gas outlet. [SSLC July, 2018-19]
Ans:
18. Explain the principle and working of a biogas plant.
Ans: The waste of living organisms like cow dung, various plant materials like the residue after harvesting of crops, vegetable waste and sewage etc. form biomass. During the decay of biomass, in the absence of oxygen, biogas is produced in the biogas plant. Slurry of cow dung and water is made in the mixing tank from where it is fed into the digester. In the digester tank, anaerobic micro-organisms decompose complex molecules of cow dung slurry and produce biogas.
19. List two ways in which animal dung can be utilized as a fuel. Out of these two which one do you think is better? Justify your answer.
Ans: Two ways:
(i) as cow dung cakes,
(ii) as biogas. Biogas is better than cow dung cakes because it has high heating capacity and are non-polluting as it burns without smoke and leaves no residue like ash. Slurry left in the biogas plant is a good manure for fields.
20. Differentiate between renewable and non-renewable sources of energy. Give two examples of each.
Ans: Difference between renewable and non-renewable sources of energy:
21. If energy can neither be created nor destroyed, explain with an example why we should worry about our energy resources?
Ans: Energy used is dissipated in less usable form. The energy used is consumed and cannot be used again. Example: Burning of candle light + heat but products cannot produce chemical energy.
22. What is a solar cell? Why and how is a solar cell application and panel prepared? List two limitations of these panels.
Ans: Solar cell is a device that converts solar energy into electricity. Since the output of a single solar cell is quite small, a large number of solar cells are combined using silver for the interconnection. This arrangement of solar cell is called solar panel that can deliver enough electricity for practical use. Uses: (i) Artificial sateffites
(ii) Traffic lights, calculators
(iii) Radio and wireless transmission
(iv) At TV relay station. Limitations: (i) Highly expensive (ii) Fabrication is a complex process (iii) Low efficiency.
23. Explain the term geothermal energy’. How can it be exploited? Though it is economical yet it is not harnessed in most of the countries. Why? OR Explain geothermal energy. How can it be harnessed to produce electrical energy?
Ans: Geothermal energy is heat energy trapped in hot regions called hot spots when molten rocks are pushed upwards. When underground water comes in contact with hot spots, steam is generated. Steam trapped in rocks is routed through a pipe to a turbine to generate electricity. Very few commercially viable sites are available where such energy can be exploited.
24. Out of the two elements A and B with mass number 2 and 235 respectively, which one is suitable for making:
(i) A nuclear reactor
(ii) A hydrogen bomb. Name the nuclear reaction involved in each case. Write one difference between the two types of nuclear reactions.
Ans: Nuclear reactor: Element B Process: Nuclear Fission Hydrogen bomb: Element A Process: Nuclear Fusion
25. Describe how a hydropower plant produces electricity Write any two advantages of hydroelectric energy.
Ans: High rise dams are constructed on the river to obstruct the flow of water and thereby collect water in large reservoirs, the water level rises and in this process the kinetic energy of flowing water gets transformed into potential energy. The water from the high level in the dam is carried through pipes to the turbines, at the bottom of the dams and converted to electricity.
26. Name the process by which nuclear energy is generated and also name one substance used for it. Give two advantages and two hazards of nuclear energy. [SSLC July, 2018 – 19]
Ans: The process is nuclear fission. Substaiices are uranium, plutonium, and thorium. Advantages: (i) For a given amount of fuel, the amount of energy released is extraordinarily large. (ii) Nuclear power plants can be set up at any place. Hazards: (i) Improper nuclear waste storage and disposal result in environmental contamination. (ii) Further there is a risk of accidental leakage of nuclear radiation.
27. Biomass is the material contained in the bodies of plants and animals. It includes the waste from trees and grass, crops, forestry, agricultural and urban wastes. The excreta of living organisms and their bodies after death also contribute biomass. (i) Comment on the statement “Biomass is a fuel”. Justify the statement by giving two reasons. (ii) What is Bagasse?
Ans: (i) Reasons: (a) It is a traditional source of energy which is used in domestic as well as industrial area. (b) Usually firewood is burnt in traditional Chulhas. (ii) Bagasse is a residue of sugarcane after extracting juice from them.
28. Explain generation of electricity in a thermal power plant OR Mention the transformation of energy that takes place in a thermal power plant. Briefly.
Ans: Large amount of fossil fuels are burnt everyday in power stations to heat up water to produce steam which further runs the turbine to generate electricity. Many thermal plants are set up near coal or oil fields. In these plants fuel is burnt to produce heat energy which is converted into electrical energy.
29. Draw a well labelled diagram of a solar cooker Identify two components in its structure that
helps in maximizing heat absorption in it.
Ans: Plane mirror, glass sheet, painted black inside the cooker. A Solar Cooker: (i) Its black surface absorbs more heat (ii) Focused mirror.
30. Can any source of energy be pollution-free?
Ans: No source of energy can be called pollution free. It is because; the use of any source of energy will disturb the environment in one or the other way. For example, solar cell. It is free of pollution but its installation may cause some damage to the environment.
Textbook Exercises:
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
Ans: (b) a cloudy day
2. Which of the following is not an example of a biomass energy source? (a) Wood (b) Gobar gas (c) Nuclear energy (d) Coal
Ans: (c) Nuclear energy
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
Ans: (a) geothermal energy
4. Compare and contrast fossil fuels and the Sun as direct source of energy.
Ans:
5. Compare and contrast biomass and hydro electricity as sources of energy.
Ans:
6. What are the limitations of can be shown in single me energy from: (i) The wind (ii) Waves (iii) Tides
Ans: (i) Limitations of extracting energy from the wind: Wind flowing with a sufficient speed is not available everywhere and all the time.
(ii) Limitations of extracting energy from ocean waves: Wave energy would be commercially viable only at places where the waves are strong. The energy produced from waves has to be transmitted through long distances at the possible of use.
(iii) Limitations of extracting energy from tides : There are very few sites suitable for harnessing tidal energy. The rise and fall of water during tides is not very large. So, large scale generation of electricity is not possible.
7. On what basis would you classify energy sources as: (i) Renewable and non-renewable?
(ii) Exhaustible and inexhaustible? Are the options given in (a) and (b) the same?
Ans: (i) Energy sources can be classified as renewable and non-renewable on the following basis: (a) Quantity available in nature (b) Mode of replenishment (c) Rate of consumption
(ii) Energy source can be classified as exhaustible and inexhaustible sources of energy on the basis of the rate of consumption and replenishment:
(a) If the rate of consumption is higher than the rate of replenishment, then the source of energy is exhaustible.
(b) If the rate of consumption is lower than the rate of replenishment, then the source of energy is inexhaustible. Thus the options given in (a) and (b) are essentially the same.
8. What are the qualities of an ideal source of energy?
Ans: An ideal source of energy is one which:
(i) Provides a large amount of energy per unit volume or mass.
(ii) Is easy to store and transport
9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Ans: Advantages of solar cooker: (i) Solar cooker causes no pollution.
(ii) Solar cooker saves fuel like wood, LPG, kerosene oil etc. Disadvantages of solar cooker:
(i) Food cannot be cooked on a cloudy day and at night.
(ii) Large amount of food cannot be cooked using solar cooker. Solar cooker will have limited utility at the places where sun shines for a shorter period of time.
10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Ans: (i) Burning of fossil fuels to meet increasing demand of energy results in air pollution. (ii) Construction of dams on rivers to generate hydro electric energy which leads to the destruction of ecosystem. In order to reduce energy consumption:
(i) Use fossil fuels with Care and Caution.
(ii) Use fuel saving devices like, solar cooker.
(iii) Consumers energy economically as energy saved in energy produced_
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