Class X Solution of SOURCES OF ENERGY

I. Very short answer type questions:  

1. Name one fuel used in a nuclear reactor.
   Ana. Uranium.
2. Define solar panel.
   Ans. A solar panel is a device that is a collection of solar cells and is used to absorb the sun's rays and convert them into electricity or heat.   
3. List any two limitations on harnessing wind energy.
   Ans. Two limitations are : 
   (i) The production of a single windmill is so small and 
   (ii) cannot be used for commercial purposes.
4. Name two combustible components of biogas.
   Ans. Two combustible components of biogas are methane and hydrogen.
5. A black surface absorbs more heat radiation as compared to a white or a reflecting surface under identical conditions. List two solar devices that make use of this property in their design.
   Ans. Solar cookers and solar water heaters.   
6. A student constructed a box-type solar cooker and convert it with the glass plate. Write the purpose served by the glass plate in the cooker.
   Ans. The purposes served by the glass plate in the cooker is to trap the solar heat and create a greenhouse effect. 
7. Mention the purpose of blackening the interior of a solar cooker.
   Ans. The purpose of blackening the interior of a solar cooker is to trap the solar heat and produce high temperatures.
8. Mention two different ways of harnessing energy from the ocean.
   Ans. Two different ways of harnessing energy from the ocean are tidal energy and ocean thermal energy. 
9. Name an efficient fuel obtained from cow dung and other animal and plant wastes. Also, mention its main constituent.
   Ans. Biogas is an efficient fuel obtained from cow dung and other animal and plant wastes. Its main constituents are methane, carbon dioxide, hydrogen, and hydrogen sulfide. 
10. Name the two major components present in the leftover slurry of a biogas plant. 
    Ans. Phosphorous and nitrogen are the major components present in the leftover slurry of a biogas plant.
11. Why is the outer surface of a solar cooker black? And name one more such device.
    Ans. The outer surface of a solar cooker is black because a black surface absorbs more heat than a white and produce high temperatures. One more such device is a solar water heater. 
12. Name any two elements that are used in fabricating solar cells.
    Ans. The two elements of silver and silicon are used to fabricate and manufacture a solar cell.
13. Name the reaction responsible for large energy produced in the sun.
    Ans. Nuclear fusion (in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles) is the reaction responsible for large energy produced in the sun.
14. Mention the main purpose of using a plane mirror in the solar cooker.
    Ans. The main purpose of using a plane mirror in the solar cooker to reflect the sun's rays.
15. Write the purpose served by a glass plate in the cooker.
    Ans. The purposes served by a glass plate in the cookers create the greenhouse effect and helps in maintaining the temperature inside the solar cooker high.
16. List two forms of energy in which solar energy manifests itself in the ocean.
    Ans. Ocean Thermal Energy and Tidal Energy are the two forms of energy in which solar energy manifests itself in the ocean.
17. State the necessary conditions to operate an Ocean thermal energy conversion plant.
    Ans. Ocean-thermal-energy conversion plants can work if the difference between the temperature at the surface water and the water at depth is 2km 20°C or more.
18. List two indirect ways of using solar energy.
    Ans. Two indirect ways of using solar energy are thermal energy and electric energy. 
19. State the transformation of energy taking place in a solar cell panel.
    Ans. Solar cells made up of silicon of solar panels absorb the sun's rays and convert them into electricity and heat.
20. Write the full form of CNG. What are the two disadvantages of burning fossil fuels?
    Ans. The full form of CNG is compressed natural gas. The two disadvantages of burning fossil fuels are acid rain and air pollution.
21. Write the sequence of events taking place in a biogas plant.
    Ans.  Cow-dung and water solutions are mixed in a tank and poured into a sealed chamber → Microorganisms decompose cow-dung solution by anaerobic respiration → after some days to produce biogases. 
22. Mention any two limitations of using fossil fuels.
    Ans. Two limitations of using fossil fuels are : (i) there are only limited reserves of fossil fuel and (ii)they are non-renewable sources of energy.

II. Short answer type questions: 

1. Give two advantages of using nuclear energy.
   Ans. (i) It does not generate any greenhouse gases like carbon dioxide, carbon monoxide, methane, ozone, etc.
   (ii) A large amount of energy can be produced by using a small amount of nuclear fuel.
2. Hydrogen is used as rocket fuel. Why? Is it a clean fuel than CNG? Why or why not?
   

   Ans. Hydrogen is used as a rocket fuel because it is a very explosive gas. Hydrogen is a cleaner fuel than CNG because of the burning of hydrogen gas only water vapour is formed which is not harmful to the environment but on the burning of CNG to produce carbon dioxide and water vapour because CNG contains methane.
3. Name the major constituent of biogas.
   Ans. The major constituents of biogas are methane, carbon dioxide, hydrogen, and hydrogen sulfide.
4. List two reasons which limit the uses of solar cell for harnessing energy for domestic use.
   Ans. (i) The domestic use of solar cells is limited due to its very high cost.
   (ii) The efficiency of the conversion of solar energy to electric energy is very low.
5. List any four qualities of an ideal source of energy.
   Ans. Four qualities of an ideal source of energy are:
   (i) A source of energy can provide an adequate amount of useful energy at a steady rate over a longer period of time.
   (ii) Easy to store and transport. 
   (iv) It should be safe and convenient to use.
   (v) It should be economical. 
6. Biogas is considered to be a boon to the farmer. Give reasons.
   Ans. (a) Farmers can produce clean fuel from bio-wastes. 
   (b) The spent slurry can be used to generate electricity. 
   (c) The remains of these wastes in biogas plant can be used by the farmer as manure.
7. List two limitations of using a solar cooker.
   Ans. Two limitations of using a solar cooker are :
   (ii) The cooking is very slow.
   (i) These devices are useful only at certain times during the day.
8. What is a nuclear fission reaction? 
   Ans. The nucleus of a heavy atom such as plutonium, thorium, uranium etc.when bombarded with low-energy neutrons, it splits into lighter nuclei and a tremendous amount of energy is released, this process is known as nuclear fission.
9. What is a nuclear fusion reaction?
   Ans. Nuclear fusion is a reaction in which two or more atomic nuclei of light elements are combined to form heavier elements of one or more different atomic nuclei and subatomic particles neutrons or protons.
10. List any two advantages of nuclear fusion reactions.
    Ans. Two advantages of nuclear fusion reactions are:
    (i) It is a safer process,
    (ii) This process releases a tremendous amount of energy.
11. Large scale use of nuclear energy becomes prohibited due to some hazards. State any two measures hazards associated with a nuclear power plant.
    Ans. Continually increase in global warming causes air pollution which weekends the strength of Earth capability and with a nuclear power plant which releases harmful gasses like carbon dioxide, carbon monoxide, etc. and pollutes water bodies which may lead to hazards such as the aquatic system may be destroyed and lead to global warming.
12. A student constructed a model of a box-type solar cooker. He used a transparent plastic sheet to cover the open face of the box. He found that this cooker does not function well. What could be the possible drawback in his model? List any four drawbacks.
    Ans.
13. List four gases generated in a biogas plant.
    Ans. Four gases generated in a biogas plant are :
    (i) Carbon dioxide,
    (ii) Methane,
    (iii) Hydrosulphide, and
    (iv) Hydrogen.
14. List three characteristics to prove it as an excellent fuel.
    Ans. (i) An excellent fuel does a large amount of work per unit volume or mass, 
    (ii) can be easily accessible
    (iii) can be easy to store and transport, and
    (iv) be economical.
15. List any four reasons why we need to look for alternative sources of energy.
    Ans. Four reasons, we need to look for alternative sources of energy are : 
    (i) There are only limited reserves,
    (ii) Fuels are non-renewable sources of energy, 
    (iii) Air pollution caused by the burning of coal or petroleum products,
    (iv) Fossil fuels are acidic oxides that lead to acid rain.
16. Why is charcoal considered to be a better fuel than wood?
    Ans. Charcoal is considered to be a better fuel than wood because:
    (i) Charcoal burns without flames and smoke,
    (ii)It has a higher heat generation efficiency.
17. List any two disadvantages of using fossil fuel.
    Ans. Two disadvantages of using fossil fuel are :
    (i) Air pollution caused by the burning of coal or petroleum products, and
    (ii) Fossil fuels are acidic oxides that lead to acid rain.

III. Long answer type questions: 

1. List two ways in which animal dungs can be utilized as a fuel. Out of these two which one do you think is better? Justify your answer.
   Ans. The two ways in which animal dungs can be utilized are 
   (i) as a cow-dung cake and 
   (ii) as a bio-gas.
   Biogas is an excellent fuel as it contains up to 75% methane. It burns without smoke, leaves no residue like cow-dung on burning. Its heating capacity is high. A lot of smoke is given out when a cow-dung cake is burnt.
2. Explain Ocean Thermal Energy and how can it be organized? Mention any two limitations in obtaining the energy from the oceans.
   Ans. The difference in the temperature of water at the surface of the ocean which is heated by the sun and water at the depth that is relatively cold is used to obtain energy in the ocean known as ocean-thermal-energy and this energy is used in the process of OTEC ( Ocean-thermal-energy conversion) to produce electricity.
   Hot surface-water is used to boil ammonia which is a volatile liquid. The vapor of this liquid is used to drive a generator's turbine. Coldwater is pumped from the depths of the ocean and condenses the vapor again into a liquid.
   Limitation -  (i) Energy efficiencies from the ocean are large, but efficient commercial exploitation is difficult.
   (ii) Ocean-thermal-energy conversion plants can work if the difference between the temperature at the surface water and the water at depth is 2km 20°C or more.
3. Explain the principle and working of a biogas plant.
   Ans. Principle-In the absence of oxygen crop residues, sewage and vegetable waste are decomposed by anaerobic microorganisms into a digester tank to deliver bio-gas. 
   Preparation of biogas in a biogas plant - The plant has a dome-like structure of bricks. Cow-dung and water solutions are mixed in a tank from where it is poured into the digester which is a sealed chamber that does not contain oxygen. Microorganisms decompose a complex compound of the cow-dung solution by anaerobic respiration that takes some days to produce gases such as methane, carbon dioxide, hydrogen, and hydrogen sulfide in the dissolved process. Biogas is stored in a gas tank that is present above the digester and is then drawn through a pipe for use. Phosphorous and nitrogen are the major components present in the leftover slurry of a biogas plant.
4. Explain geothermal energy. How can it be harnessed to produce electrical energy?
   Ans. Geothermal energy is heat energy that is generated and stores on the earth's surface.
   Due to geothermal energy molten rocks are formed in the deeper and these molten rocks formed hot regions of earth’s crust called ‘hot spots’ and sometimes hot water from that region finds outlets are known as hot springs. When underground water comes in contact with the hot spot, steam is generated and the steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity.
5. Energy can neither be created nor be destroyed. In the context of this statement explain, why do we talk about the energy crisis?
   And.  According to the 'mass conservation law' energy can neither be created nor destroyed, energy can only be transferred and total energy remains the same. 
   For example- If we light a candle, the chemical energy in the wax is converted to heat energy due to exothermic reaction and light energy on burning. The other products carbon dioxide and water vapour are obtained and the total energy during a physical or chemical process remains the same.
   Any source of energy we use, to do work, is consumed and cannot be used again because the energy in the usable form, is dissipated to the surroundings in less usable forms. So we talk about the energy crisis.
6. List in tabular form to distinguishing features between renewable and nonrenewable sources of energy. Give two examples of each.
   Ans. 

   Renewable sources	Non-renewable sources
   These sources can be utilized continuously over a very long period of time,	These sources  cannot be utilized continuously over a very long period of time,
   They are the non-conventional sources,	They are the conventional sources,
   These are the natural sources which will not get exhausted,	These are the natural sources which would soon deplete if they are consumed indiscriminately,
   These sources can be regenerated,	These sources cannot be regenerated,
   Examples: Water, air, sunlight etc.	Example: Mineral, oil,  coal, etc.

7. I. Name the device used to convert: (a) Solar energy into heat (b) Solar energy into electricity 
   II. Mention two limitations of solar energy.
   Ans. I. The device used to convert: 
   (a) Solar energy into heat - Solar cooker and heater. 
   (b) Solar energy into electricity - Solar cells or solar panels. 
   II. Limitation of solar energy- 
   The efficiency of conversion of solar energy to electricity is low
   It produces d.c. electricity which cannot be directly supplied for household purposes.
8. Draw a geometric level diagram of a box-type solar cooker. Name two components of the solar cooker which are responsible to increase the temperature inside the Solar Cooker. Explain their function.
   Ans. 
   
   Solar Cooker
   
   Two components of the solar cooker that are responsible to increase the temperature inside the solar cooker :
    (i) The glass plate in the cookers create the greenhouse effect and helps in maintaining the temperature inside the solar cooker high. 
   (ii) Blackening the interior of a solar cooker is to trap the solar heat and produce high temperatures.
9. Mention why is it not possible to make use of solar cells to meet all our energy needs. State three reasons to support your answer.
   Ans.  During day time solar cells are useful and can convert solar energy into electricity. Normally a cell develops a  0.5–1 V and can produce about 0.7 W of electricity in the presence of the Sun. A large number of solar cells when combined in an arrangement, a solar panel is formed that delivers enough electricity for practical use. Special grade silicon and silver are used for making solar cells, which are very expensive. In spite of the high cost and low efficiency, solar cells are not possible to make use of solar cells to meet all our energy needs.
   Three reasons are:
   (i) The domestic use of solar cells is limited due to its very high cost.
   (ii) The efficiency of the conversion of solar energy to electric energy is very low.
   (iii) A solar cell produces direct current (D.C) electricity that cannot be supplied for a household purpose directly.
10. 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.
    Ans. The process by which nuclear energy is generated is nuclear fission.
    When the nucleus of a heavy atom is bombarded with low-energy neutrons, it splits into lighter nuclei and a tremendous amount of energy is released. This process is known as nuclear fission.
    Uranium is the one substance used for it.
    Advantage- (i) It does not generate any greenhouse gases like carbon dioxide, carbon monoxide, methane, ozone, etc.
    (ii) A large amount of energy can be produced by using a small amount of nuclear fuel.
    Disadvantages- (i) The first hazard is the storage and disposal of used fuels because the uranium still decaying into harmful radiations that result in environmental contamination.
    (ii) Second is the risk of accidental leakage of nuclear radiation which is a high risk of environmental contamination.
11. Explain how does burning fossil fuels causes air and soil pollution.
    Ans. The burning of fossil fuels like coal or petroleum products causes air pollution which causes the greenhouse effect of gases like carbon dioxide. The burning of fossil fuels releases harmful gases and ashes into the surroundings. Oxides of carbon, nitrogen, and sulfur are released into the air by burning fossil fuels which are acidic oxides and when it comes in contact with rainwater leads to acid rain. Acid rain affects our water and soil resources. 
12. Describe how hydropower plant produces electricity is?
    Ans. In hydropower plants, the potential energy of water at high altitude and the kinetic energy of flowing water is used to make electricity. Hydropower plants convert the potential energy or kinetic energy of falling water into electricity.
    To produce electricity, high-rise dams are constructed on the way of the river to obstruct the flow of water and to collect water in larger reservoirs. The water level rises and the kinetic energy of flowing water gets changes into potential energy. The water from the high level in the dam is carried through pipes, to the turbine, at the bottom of the dam. When the turbine rotates electricity formed. In this process, the kinetic energy possessed by the flowing water is called the hydro energy.
13. Write any two advantages and disadvantages of hydroelectric energy.
    Ans. Two advantages of hydroelectricity-
    (i) It is a renewable source and it does not cause any pollution in the environment.
    (ii) The dams constructed over rivers help in irrigation and control of floods.
    Two disadvantages - 
    (i) The vegetation is submerged rots due to anaerobic conditions and produces large amounts of methane gas which is a greenhouse gas. 
    (ii) Due to the construction of dams over the rivers large echo-systems are destroyed.
14. 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 directly into electric energy.
    They can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable. 
    A large number of solar cells are made up of silicon and zinc, combined in an arrangement that makes a solar panel that converts solar energy into electricity for practical use. silicon converts solar energy into electric energy and silver used for the interconnection of the cells in the panel.
    Two limitations: The cost of a solar cell is high and these devices are useful only at certain times during the day.
15. How can geothermal energy be used commercially?
    Ans. The energy possessed by the hot water below the earth is called Geothermal energy. 
    Due to geological changes, molten rocks formed in the deeper hot regions of the earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’. When underground water comes in contact with the hot spot, steam is generated. The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity.
16. List in tabular form 3 distinguishing features between a thermal power plant and a geothermal power plant.
17. Ans. 

    Thermal power plant	Geothermal power plant
    1. In thermal power plant fuel is burnt to produce heat energy to heat up water to produce steam which helps to runs the turbine to generate electricity.	In geothermal power plants, the heat of the earth is used to heat up water to produce steam which helps to runs the turbine to generate electricity.
    2. The cost of production is expensive.	2. The cost of production would not be much
    3. It causes pollution in the environment.	3. It does not cause any pollution in the environment

18. Out of the two elements A and B with mass numbers 2 and 235 respectively, which one is suitable for making (a) a nuclear reactor (b) a hydrogen bomb. Name the nuclear reaction in each case. Write one difference between the two types of nuclear reactions.
    Ans. The element B is Uranium, suitable for a nuclear reactor and nuclear reaction is nuclear fission.
    Nuclear fission- When the nucleus of a heavy atom, such as uranium, thorium or plutonium, is bombarded with low-energy neutrons, it splits into lighter nuclei and a tremendous amount of energy is released. This process is known as nuclear fission.
    The element A is Helium, suitable for a hydrogen bomb and nuclear reaction is nuclear fusion.
    Nuclear fusion- Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles and this reaction are responsible for large energy produced in the sun.
    Difference between nuclear fission and fusion - In nuclear fusion, two or more atomic nuclei are combined to form one or more different atomic nuclei whereas in nuclear fission the nucleus of a heavy atom it splits into lighter nuclei.
19. It has been observed that the construction of big dams has certain problems associated with them. List three problems.
    Ans. Disadvantages of constructions of dams - Constructions of big dams have certain problems.
    (i) Large areas of agricultural land or large eco-systems are destroyed when they submerge underwater.
    (ii) The vegetation, which is submerged, decomposes due to anaerobic conditions and gives rise to large amounts of methane gas which is a greenhouse gas.
    (iii) This creates problems in the human habitation of the displaced.
20. Describe how hydrogen-energy can be converted into electrical energy. Write any two limitations of hydrogen energy.
    Ans. Hydropower plants convert the kinetic energy of flowing water or the potential energy of falling water at a height into electricity. Flowing water further runs the turbine to generate electricity. The turbine is a device that has one moving part called rotor-blade assembly. The moving water acts on the blades to spin them with a speed that would turn the shaft of the dynamo and convert the mechanical energy into electrical energy.
    Two limitations: (i) It works only in the presence of water bodies.
    (ii) Electricity produced by this process is not enough.
21. Draw a neat diagram of the biogas plant and label.
    (a) inlet of slurry (b) digester and(c) gas outlet.                          Ans.
22. List three factors responsible for the wind. State three limitations in harnessing wind energy.
    Ans. Three factors responsible for wind are:
    (i) The uneven heating of landmines and water bodies by solar radiation,
    (ii) Differences in atmospheric pressure, and
    (iii) Rotation of earth.
    Three limitations in harnessing wind energy - 
    (i) Wind energy farms can be established only at those places where the wind blows for the greater part of a year and the wind speed should also be higher than 15 km/h to maintain the required speed of the turbine. 
    (ii) Wind energy farms required a large area of land to establish wind energy farms for a 1 MW generator which may be expensive.
23. State the energy transformation taking place at hydropower plants. List two advantages of the setting of hydropower plants.
    Ans. The energy transformation taking place at hydropower plants are:
    (i) Potential energy to mechanical energy- When stored water (potential energy) of the dam falls on the turbine blade to spin them with a speed that would turn (mechanical energy) the shaft of the dynamo. 
    (ii) Mechanical energy to electrical energy - Moving dynamo (mechanical energy) convert mechanical energy into electrical energy.
    Two advantages: (i) It does not cause any pollution and it is a renewable source of energy.
    (ii) The dams constructed over rivers help to control floods and helps in irrigation.