1. A good source of energy is one that is able to provide large amount of work per unit volume or mass, be easily accessible at economical rate and can be easily stored and transported.
2. Conventional sources of energy: Fossil fuels, coal, petroleum, natural gas (thermal power plants), energy of flowing water (hydrowater plants), biomass, cow-dung, plants and vegetable wastes (bio-gas plants), wind energy (windmill).
3. Fossil fuels: Any naturally occurring organic fuel formed in the Earth’s crust, such as petroleum, coal and natural gas are called fossil fuels.
4. Alternate or non-conventional sources of energy: Solar energy-energy derived from sun, Nuclear energy-fission of radioactive substances, Geo-thermal energy-energy derived from hot spots under the earth, Ocean energy-ocean thermal energy, wave energy.
5. Non-renewal sources of energy: Fossil fuels like coal, petroleum and natural gas non-renewable.
6. Thermal power plants: Thermal power plants should be preferably located near coal or oil fields. It is easier to transport electricity than the fuel.
7. Hydropower plants: Convenient location to build dams. Potential energy of falling water is converted into electricity.
8. Biomass: The plant and animal products, which act as the source of fuel is said to be biomass.
9. Biogas: Cow-dung, various plants materials like the residue after harvesting the crops, vegetable waste and sewage decomposed in the absence of oxygen to give biogas (or Gober gas).
10 Biogas plants: Anaerobic micro-organisms (in the absence of oxygen) decompose complex compounds of cow-dung slurry or biomass-water mix produce biogas (60-80% methane).
11. Tidal energy: The gravitational pull of the moon on the rotating earth causes rise and fall in the level of water in the sea. The sea-level changes during the day. This phenomenon is called high and low tides and difference in sea levels gives us tidal energy. Tidal energy is harnessed by constructing a dam across narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.
12. Windmill: The power of wind (>15km/h) gives rotatory motion of the windmill which is used to turn the turbine of the electric generator. The output of a single windmill is quite small and so a number of windmills are to be erected over a large area.
13. Nuclear reactor is a device in which a fission reaction is carried out in a controlled manner. The energy so released is used to heat water which then turns turbines and generates electricity. (Note: Fission of heavy radioactive isotopes gives tremendous amount of energy.)
14. Environment consequences: Sources of energy as are available produce lot of pollution in the atmosphere or cause environmental damage in other ways.
15. Quality of fuel is measured by its calorific value (heat regenerated by burning unit mass of a substance
16. Solar energy: 47% of the sun’s energy reaching the periphery of the earth’s atmosphere reaches the earth’s surface. One m2 of earth’s surface receives 1.4kJ/m2s. This is called solar constant. This energy is trapped by various means such as solar cookers, solar heaters and solar cells. A typical solar cell (using high quality silicon or silver) develops a voltage of 0.5-1V and can produce 0.7W of electricity. So a panel of solar cells is used.
Q.1. Name the largest component of biogas.
Ans. The largest component (upto75%) of biogas in methane.
Q.2. What is greenhouse effect?
Ans. The glass roof and glass walls of a greenhouse allow heat and sunlight to enter it but do not allow heat (infrared radiation) to escape. On account of this, greenhouse gets warmed.
Q.3. Name the gaseous fuel, out of the following which has the highest calorific value: Hydrogen, Methane, LPG, Biogas
Q.4.Why is CNG considered an environmental friendly fuel?
Ans. CNG does not produce toxic gases on burning.
Q.5. Name a fraction obtained during refining of petroleum which does not find use as a fuel.
Ans. Lubricating oil.
Q.6. Which of the following gases is a major constituent of biogas : Carbon monoxide, hydrogen, methane, carbon dioxide?
Ans. Methane (75%)
Q.7. What is slurry left over after generation of biogas in biogas plant used?
Ans. The slurry is rich in nitrogenous and phosphorus compounds and as such serves as an excellent manure.
Q.8. How is the increase in demand for energy affecting our environment adversely ?
Ans. We use fossil fuels to meet the increased energy demands. As a result of this, pollutants so produced adversely change the composition of the environment.
Q.9. Name the process by which energy is produced in a nuclear reactor.
Ans. In a nuclear reactor,energy is produced by the process of nuclear fission.
Q.10. Which one of the following is a renewable resource: Natural gas, petroleum, Ground water, Coal
Ans. Ground water.
SHORT QUESTIONS WITH ANSWERS (2 MARKS)
Q.1. What is solar cell ? Name two materials mostly used for making solar cells.
Ans. A solar cell is a device which converts solar energy directly into electric energy. Silicon and germanium are the two most commonly used materials for making solar cells.
Q.2. What type of mixture are separated by fractional distillation? Name the fraction of crude oil whose boiling point is more than 350oC. Where is it mostly used as a fuel?
Ans. The various components of a mixture should have different boiling points in case these are to be separated by fractional distillation. Fuel oil is the fraction of crude oil (petroleum) whose boiling point is above 350oC. It is used as a fuel in various industries to heat boilers because it does not leave any residue after burning.
Q.3.How were fossil fuels formed ? How these fossils fuels were made?
Ans. Fossil fuels were formed due to high pressure, heat and the action of anaerobic bacteria of fossils for million of years. These fuels were made form the fossils of plants and animals buried deep in the Earth.
Q.4. Define the term ‘fuel’. What are primary and secondary fuels? To which class of fuel do the following belong: Coke , Wood, Petroleum, LPG.
Ans. A material which produces heat on combustion is called a fuel.
Primary fuels. Fuels which are used directly to produce heat are called primary fuels.
Secondary fuels. Fuels which are manufactured by chemical process using primary fuels are called secondary fuels. Wood and Petroleum are primary fuels and Coke and LPG are secondary fuels.
Q.5. 48 kJ of energy is produced per minute in a nuclear reactor. Calculate the number of fissions which would be taking place in the reactor per second, if the energy released per fission is 3.2 x 10 -11J
Ans. Total energy produced/minute =48kJ =48 x 103 J
Energy produced/second = 48x103/60 j = 0.8 x 103 J
Energy released/fission= 3.2 x 10-11J.
Number of fissions/second = [Energy produced/second] / [the energy released per fission]
=0.8 x 103 J / 3.2 x 10 -11 2.5 x 1013
Q.6. Give one example of a nuclear fusion reaction. Describe one method for making such reactions possible
Ans. One example of a nuclear fusion reaction is when two deuterons fuse together to form He-3 nucleus and a neutron with the emission of a large amount of energy
21H + 2H1 --------à 3He2 +1no
This reaction is possible at extremely high temperatures (=107 K) and pressures (=107 Pa).2A1
Q.7. Which type of nuclear process is currently used in nuclear electricity generators? Give one example each for the substances used in this context as (i) coolants (ii) moderators and (iii) nuclear fuel?
Ans. In nuclear electricity generators, the process used currently involves the fission of U-235 nuclei by bombarding them with thermal neutrons. Water is one of the coolants; graphite is one of the moderators and enriched uranium is one of the nuclear fuels.
Q.8.For producing electricity, the energy from flowing water is preferred to energy obtained by burning coke. State two reasons for it.
Ans. (i) production of electricity from water is pollution free.
(ii) water energy is a renewable source of energy. Coke, on the other hand, is a non- renewable source of energy and causes pollution on burning.
Q.9. Define a nuclear fusion reaction .Describe the conditions for the occurrence of a nuclear fusion reaction. 21H + 2H1 --------à 3He2 +1no
Ans. A nuclear fusion reaction involves combining of two or more lighter nuclei to form a heavier nucleus with the liberation of a large amount of energy.
The conditions for the occurrence of a nuclear fusion reaction are:
Temperature of fusing nuclei should be raised to 107 K at pressure of millions of pascals. Or
The fusing nuclei be accelerated to high speeds using particle accelerators.
Q.10. Name the places of out country where fields of natural gas are found. Why is it called a clean fuel? Give two reasons.
Ans. Tripura, Jaisalme, off-shore area of Bombay, Krishna-Godavari Delta.
Natural gas is a clean fuel as: (1)It does not produce harmful gases on burning,(ii) It burns without smoke and does not leave any residue after burning.
Q.11. What is the cause of release of unusually large energies in nuclear fission reactions? How is the energy per fission calculated?
Ans. In nuclear fission reactions, a creation mass disappears. This is called mass defect (Δm). It appears in the form of energy according to Einstein equation,E=( Δm)c2,where c is velocity of light in vacuum. To calculate energy per fission, we sum up the masses on left hand side of the fission reaction; and also on the right hand side of the fission reaction. The difference in masses on the two sides of the reaction gives us mass defect (Δm). Usually, this mass defect is in atomic mass unit (u).
As 1 u = 931 Me V, we can calculate energy released/fission in MeV) by multiplying (Δm) by 931.
Q.12. The use of dry wood as domestic fuel is not considered as good. State two reasons for it.
Ans . (i) Wood produces lot of smoke on burning.
(ii)It leaves lot of residue after burning.
Q.13. In one fission of uranium, 3x10-11 J of energy is made available. Calculate the total number of fissions necessary per second to generate power of 15 kW.
Ans. Energy released/fission =3x10-11 J.
Total energy required/s = 15 kW = 15000W =15000 J/s.
Number of fissions/s = [Total Energy/Second] ÷ [Energy/fission] = 15000 ÷ 3x10-11 J = 5 x 1014
Q.14.How is charcoal obtained from wood? Why is charcoal considered better fuel than wood?
Ans. Charcoal is obtained from wood by destructive distillation of wood. When wood is strongly heated in the absence of air, the residue left behind is called charcoal.
Charcoal is better fuel than coal due to the following reasons:
(1)No harmful gases are produced on burning charcoal (ii) No residue is left after it has burnt itself out.
(iii) It has a higher calorific value.
Q.15. Describe how hydro energy can be converted into electrical energy. Write any two limitations by hydro energy.
Hydro power plants :-
In hydro power plants water from rivers are stored by constructing dams. The water from the dam flows down through pipes and rotates the turbines of generators to produce electricity.
Two limitations by hydro energy. i) The initial cost is high. ii) It causes displacement of people from large areas of land.
Q16.what is geothermal energy? What are its advantages?
The deeper regions of the earth’s crust is very hot. This heat melts rocks and forms magma. The magma moves up and collects below at some places called Hot spots. The underground water in contact with hot spot gets heated into steam at high pressure. By drilling holes into hot spots the steam coming out can be used to rotate turbines of generators to produce electricity.
SHORT QUESTIONS WITH ANSWERS (3 MARKS)
Q.1. How many groups of nuclei are generated in the fission of 235 U? what are their characteristics? Explain briefly the terms (i) prompt (ii) delayed, and (iii) spontaneous fission.
Ans. Two groups of nuclei are generated in the fission of 235 U
(i)One of these groups is a heavy group of nuclei with mass numbers ranging from 130 to 149,e.g., Barium and Lanthanum.
(ii)The other groups are a lighter group of nuclei with mass numbers ranging from 85 to104, e.g., Krypton and Molybdenum.
(iii)In prompt fission, the heavy nucleus disintegrates the moment it is bombarded.
(iv)In delayed fission, a projectile (e.g., neutron) enters the target nucleus and causes an instability which results in the fission of the target nucleus after a short while.
(v) Spontaneous fission is just out of the nature of the element.
Q.2. Write the four processes that can take place, after neutrons are emitted in a fission reaction. Which of these processes will cause the fission to continue? How is the energy of released neutrons lowered from 2 Me V to 0.025 Me V?
Ans. The four process that can take place after neutrons are emitted in a fission reaction are :
- At least one such neutron hits another nucleus to cause its fission releasing more neutrons.
- The neutrons may be captured by other nuclei without causing their fission.
- The neutrons may be captured by other nuclei (present either in the fissionable material or in the surrounding container without causing fission.
- The neutrons may not interact with other nuclei and may escape the system.
- The energy of released neutrons is lowered from 2Me V to0.025Me V by passing them through a moderator.
Q.3. (i) write the value of solar constant of sun. (ii) what type of mirror is used in Box Type Solar cooker? (iii) why it is difficult to use hydrogen as a source of energy? (iv)what is the maximum temperature attained in a concave reflector type solar cooker? (v)Fossil fuels are classified as non-renewable source of energy. Explain why.
Ans. (i) 1.4kW/m2 (ii) Plane mirror. (iii) It cannot be stored safely as (i) it burns with explosion and(ii) has low ignition temperature. (iv) about 200oC. (v)fossil fuels cannot be replenished. It takes millions of years for their formation.
Q.4. (a) Why is solar cooker box covered with a plane glass plate? (b) Why is the energy of water flowing in a river considered to be an indirect form of solar energy? (c) Write one advantage of nuclear fission reaction.
Ans. (a) the plane glass plate traps heat radiation and thus produces a kind of greenhouse effect. Consequently, the temperature inside the cooker become high (100oC to140oC).
(b) Solar energy changes into potential energy of water vapour rising in the atmosphere during evaporation of water from rivers, seas, oceans and other water masses. The water vapour from clouds and also cover mountains with snow. When the clouds bring rain and the snow on the mountains melts, their potential energy changes into kinetic energy of water flowing in the rivers and streams.
(c) Amount of energy produced in nuclear fission is enormous, one kg of U-235, on fission produces as much energy as 2500 tons of coal produces on combustion.
Q.5. (a) State one limitation of solar energy available from solar cells. (b) What is the minimum wind velocity required to obtain useful energy with a wind will ? (c) Define the term ‘nuclear fission’.
Ans. (a) the electricity (dc) produced by solar cells panels is stored by charging dc batteries which can be used only to operate dc devices. To operate any ac device, this dc has to be first converted into ac by using inverters.
(b) 15km/h (c) Nuclear fission- In Nuclear fission, the heavy nucleus distingerates, the Moment it is bombarded with law energy neutrons, it splits up into two Righer nuclei and tremendous amount of energy is released.
Extra score questions
Q.1. Name two gases, other than carbon-dioxide that are given out during burning of fossil fuels and contribute towards acid rain formation?
Ans. Sulphur dioxide and Nitric oxide.
Q.2. Why are many thermal power plants set up near coal or oil fields?
Ans. Coal or petroleum is used to heat water to generate steam required for running for turbines in thermal power plants. Thus, if thermal power plants are set up near coal or oil fields, the cost of transportation of coal or petroleum is greatly reduced.
Q.3. Justify in one sentence that hydropower (hydel electricity) is a renewable source of energy.
Ans. Hydropower is generated from water flowing out of the dam which gets filled up again when it rains (or the snow melts) through the rivers which supply water to the dam.
Q.4. Out of two solar cookers, one was covered by a plane glass slab and the other was left open. Which of the two solar cookers will be more efficient and why?
Ans. The solar cooker covered by plane glass slab will be more efficient than the one which is left open. This is due to the reason that the plane glass slab enables the cooker to trap heat inside it. On this account, the temperature inside the cooker rises. In fact, the plane glass slab placed on the cooker produces a kind of greenhouse effect.
Q.5. A student constructed a box type solar cooker. He found that it did not work efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the cooker. What maximum temperature can ordinarily be reached inside a solar cooker?
Ans. The four possible mistakes in the construction and operation of the cooker are:
- The interior of solar cooker might not have been blackened,
- Plastic cover might have been used instead of glass cover,
- The cooker might not have been properly insulated,
- The cooker utensils might not have been blackened.
Ans. (i) Black painted aluminum sheet absorbs heat radiation
(ii) Glass wool, which is a bad conductor of heat, prevents the loss of heat.
(iii) Glass sheet traps the heat radiation in the box.
(iv)Mirror plate reflects the heat radiation onto the glass sheet.
Q.7. Solar energy can be harnessed directly as well as indirectly. Give two examples of each type.
Ans. Solar energy is used directly as heat or by converting it directly into electricity. Examples: solar cooker (or solar water heater) and solar cell panels. Solar energy is used indirectly by converting it into chemical energy (like biomass energy), harnessing the energy of wind, sea waves, tides and ocean thermal energy. Example: Biogas plants and windmills.
Q.8. What is anaerobic degradation?
Ans. Anaerobic degradation is the process of decomposition of animal and plants wastes by anaerobic bacteria in the presence of water but in the absence of air to form methane (the main constituent of biogas), carbon dioxide, hydrogen and hydrogen sulphide. Anaerobic bacteria (or anaerobe) is a minute organism that can live without free oxygen.
Q.9. what is a solar power plant? Name one such plant in our Country.
Ans. Sunlight is concentrated on black painted pipes (filled with water) with the help of concave reflectors. Due to solar heat, water starts boiling and then changes into steam. The steam so produced rotates a steam turbine which drives a generator to produce electricity. A solar thermal power plant of 22k W capacity is in operation at Solajipally village in Andhra Pradesh. A 50kW solar thermal power plant is being installed at the Twal Pahari Premises of the Solar Energy Centre, Gurgaon (Haryana).
Q.10. How can wood be made a renewable source of energy ?
Ans. Wood can be made a renewable source of energy only if trees are planted in a planned manner.
Q.11. What causes the wind to blow?
Ans. Equatorial regions on the Earth receive more solar radiation than other parts of the Earth. As such, the air at equatorial regions is hotter and rises upwards into the atmosphere. The cooler air from other regions (especially polar regions) starts blowing to the equatorial regions to fill the space vacated by hot air. It is this moving air which is called wind.
Q.12.To which category of fuel does hydrogen belongs to?
Ans. Hydrogen ,which is available in plenty in water on earth, is classified as a renewable sources of energy.
Q.13. Why is Nuclear fuel classified as renewable source of energy?
Ans. Nuclear fuel is required only in a very small quantity to generate electric power and as such is inexhaustible.
Q.14. Why the Geothermal energy is classified as a renewable sources of energy?
Ans. Geothermal energy will be available for a long time.
MCQ on SOURCES OF ENERGY
Q.1. 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 utilized further
(d) One possible method of utilizing the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator.
Q.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)
Q.3. 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.
Q.4. which one of the following forms of energy leads to least environmental pollution in the process of its harnessing and utilization?
(a)nuclear energy (b) thermal energy (c) solar energy (d) geothermal energy
Q.5. Which of the following is a non-renewable source of energy?
Q.6. 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.
Q.7. 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.
Q.8. which is the ultimate source of energy?
(c ) uranium
(d) fossil fuels
Q.9. The main constituent of biogas is
(b) carbon dioxide
Q.10. 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)
Q.11. 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.
Q12. which part of the solar cooker is responsible for green house effect?
(a) coating with black colour inside the box
(c) glass sheet.
(d) outer cover of the solar cooker
Q.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 water increases with height. (d) more water molecules dissociate into ions. Ans. (b).
Q.14. 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) Gober-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.
Q.15. Fuel used in thermal power plants is
(d) fossil fuels
QUESTIONS FOR PRACTICE
SHORT QUESTIONS FOR PRACTICE (2 MARKS)
Q.1.Write two advantage of classifying energy sources as renewable and non-renewable.
Q.2.List the four characteristics of biogas on account of which it is considered an ideal fuel.
Q.3.Discuss one limitation each for the extracting of energy from : (a)winds (b)tides
Q.4. What is biogas? Why is biogas considered an ideal fuel?
Q.5.(a) distinguish between renewable and non renewable sources of energy.
(b) choose the renewable sources of energy from the following list: coal, biogas, sun, natural gas
Q.6. What is a thermal neutron? Draw a schematic diagram depicting fission of a U-235 nucleus on absorption of a thermal neutron.
Q.7. What is nuclear fusion? Give an example for it.
SHORT QUESTIONS FOR PRACTICE (2 MARKS)
Q.1.Draw the diagram of the floating gas holder type biogas plant and mark on it the gas outlet.
Q.2. (i) Draw a schematic diagram to show essential steps in a controlled chain reaction based on fission of 23592 U.
(ii)Starting from 23592 U, describe the chain of nuclear reactions that leads to 23592 U as the final product. What is the significance of this reaction?
Q.3. (i) distinguish between renewable and non-renewable sources of energy giving one example of each. (ii) why the use of wood as a fuel not advised although forests can be replenished?
Q.4. Name the three forms in which energy from oceans is made available for use. What are OTEC power plants? How do they operate?
LONG QUESTIONS FOR PRACTICE (5 MARKS)
Q.1. With the help of a diagram, describe the construction and working of a box type solar cooker. Write two advantages and two limitations of solar cookers.
Q.2. Describe the construction of a box type solar cooker or show it with the help of a diagram. How is the rise in temperature obtained in this set up? Mention two advantages and two limitations of solar cookers.
Q.3. Draw a labeled diagram of solar cooker. What purposes are served by the blackened surface, glass cover plate and the mirror in a solar cooker? What would happen if the plane glass mirror of a solar cooker is replaced by a concave glass mirror?
Q.4. What is the basic cause for winds to blow? Name a part of India where wind energy is commercially harnessed. Compare wind power and power of water flow in respect of generating mechanical and electrical energies. What is the hindrance in developing them?
Q.5. What is the importance in India of hydroelectric plants? Describe how electric energy is generated in such plants.
Q.6. The solar constant at a place is 1.4kW/m2. How much solar energy will be received at this place per second over an area of 5m2?
Q.7. Name the major fuel component of biogas. What are its other combustible components? Draw a simple labeled diagram of a fixed dome type biogas plant. What is the use of the residual slurry and why?