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1Class-VIII Physics Question Bank

I. Tick (✔✔✔✔✔) the most appropriate answer.1. The device which directly converts solar energy to electric energy is:

(a) solar cooker (b) solar furnace(c) solar cell (d) solar water heater

2. The energy which directly changes into electric energy in solar cell is:(a) heat energy only (b) light energy only(c) heat and light energy (d) none of these

3. The kind of energy present in fossil fuels is:(a) heat energy (b) mechanical energy(c) chemical energy (d) geothermal energy

4. The ultimate source of chemical energy in fossil fuels is:(a) potential energy of water (b) kinetic energy of water(c) solar energy (d) magnetic energy

5. The renewable source of energy amongst the following is:(a) wind energy (b) hydel energy(c) solar energy (d) all the above

6. The non-renewable source of energy amongst the following is:(a) wind energy (b) hydel energy(c) solar energy (d) fossil fuels

7. The splitting of heavy nucleus of an element with the releases ofenergy is called:(a) combustion (b) fusion (c) fission (d) photosynthesis

8. The gas which is obtained from biomass:(a) LPG (b) CNG (c) Biogas (d) hydrogen

9. Bhakhra-Nangal hydel project is situated in the state of:(a) Gujarat (b) Orissa(c) Himachal Pradesh (d) Karnataka

10. The energy possessed by moving water is:(a) potential energy (b) kinetic energy(c) geothermal energy (d) hydroelectric energy

Ans. 1. (c) 2. (b) 3. (c) 4. (c) 5. (d) 6. (d)7. (c) 8. (c) 9. (c) 10. (b)

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II. Complete the following sentences.1. ________ is the waste materials produced by living beings or their

dead remains.2. The water stored in the dams on river systems has ________.3. Solar energy is responsible for wind energy and ________ energy.4. Petroleum is a ________ fuel, formed from the remains of dead

animals and plants.5. Solar cooker does not cause any environmental ________.6. Solar cell is a device which directly converts________ into electric

energy.7. At wind farms, the wind energy is harnessed in the form of _______.8. The pollutant in air responsible for acid rain is ________.9. Energy is the capacity to do ________.

10. The prime source of energy is ________.11. The first fuel to be used was ________.12. Coke is a ________ fuel.13. The gaseous fuel used for cooking are________.14. The ________ of steam is used to drive turbines in thermo electric

stations.Ans. 1. Biomass 2. Potential energy 3. Chemical

4. Fossil 5. Pollution 6. Solar energy7. Kinetic energy 8. Sulphur dioxide 9. Work

10. Sun 11. Wood 12. Fossil13. LPG and biogass 14. Heat energy

III. The statements given below are incorrect, write the correct statements.1. Wood is a non-renewable source of energy.

Ans. Wood is a renewable source of energy.2. In photovoltaic cells chemical energy is converted into electrical energy.

Ans. In photovoltaic cells solar energy is converted into electrical energy.3. In wind farms the potential energy of wind changes to electric energy.

Ans. In wind farms the kinetic energy of wind changes to electrical energy.4. Kerosene oil is a renewable source of energy.

Ans. Kerosene oil is a non- renewable source of energy.5. Nuclear energy is highly dangerous.

Ans. Nuclear wastes are highly dangerous.6. Hot spots are the places on the Earth where sun shines more brightly.


Ans. Hot spots are the places inside the earth where geothermal energy ispresent.

7. Solar cooker preserves all nutrients in food, as food cooks atcomparatively high temperature.

Ans. Solar cooker preserves all nutrients in food as food cooks atcomparatively low temperature.

8. As the water stored in dams flows out, its kinetic energy changesinto potential energy.

Ans. As the water stored in dams flows out, its potential energy changesinto kinetic energy.

9. The minimum height required for stored water is 43 m, so that itsP.E. could be converted into electric energy.

Ans. The minimum height required for stored water is 34 m, so that itsP.E. could be converted into electrical energy.

10. The biomass ferments to form methane in the presence of air.Ans. The biomass ferments to form methane in the absence of air.

11. Smoke and dust particles are not the cause of air pollution.Ans. Smoke and dust particles are the cause of air pollution.

12. Pollens floating in the air do not cause any air pollutionAns. Pollens floating in the air cause air pollution.

IV. Find the odd one out. Give reasons for your choice.1. Flowing water, tidal waves, coal, hard blowing wind.

Ans. Coal is a non-renewable source of energy while flowing water, tidalwaves and hard blowing wind are renewable sources of energy.

2. Liquefied petrol gas, biogas, compressed natural gas, hydrogen gas.Ans. Hydrogen gas is not a fuel while liquefied petrol gas, biogas and

compressed natural gas are fuels.3. Farm residues, animal dung, wood, coal.

Ans. Coal is a fossil fuel while farm residues, animal dung and wood arenot fossil fuels.

V. Match the different forms of energy with their sources.Column A Column B

1. Water power (a) obtained when the nucleus of an atom splits


2. Nuclear energy (b) obtained from sun3. Wind energy (c) obtained from water falls4. Solar energy (d) obtained from moving air

Ans. 1. (c), 2. (a), 3. (d), 4. (b)VI. Give reasons for the following.

1. Electricity is the most important form of energy in use today. Ans. Electricity is the most important form of energy used today because,

it is non-polluting, can be easily transmitted over long distances in asmall time and needs least maintenance expenses.

2. Biogas is preferable to wood or coal. Ans. Biogas is preferable to wood or coal because, it is a convenient and

clean fuel which does not produce smoke or other harmful gaseswhile wood or coal produces harmful gases and cause air pollution.

VII. Answer the following questions.1. What do you understand by the term ‘renewable source of energy?

Support your answer by at least four examples.Ans. The natural sources of energy, which are continually replenished

through a number of natural processes and will never run out arerenewable sources of energy. Examples of renewable sources ofenergy are:(i) Sun (ii) Water (iii) Wind (iv) Wood

2. What are non-renewable sources of energy? Support your answerby two examples.

Ans. The natural sources of energy, which once used up cannot bereplaced over million of years are known as non-renewable sourcesof energy. Coal and petroleum are two examples of non-renewablesources of energy.

3. How does solar energy changed into chemical energy of biomass?Ans. Solar energy is changed into chemical energy by green plants by the

process of photosynthesis.4. Answer the following questions regarding the box type solar cooker.

(a) Why is its interior painted black?(b) Why is it covered with a double plane glass lid?


(c) Why is a plane mirror reflector used?(d) What is the optimum temperature attained by this cooker?(e) State its any two advantages.(f) State its any two limitations.

Ans. (a) Since black surfaces are good absorbers of heat energy, sointerior of a solar cooker is painted black.

(b) Solar cooker is covered with a double plane glass lid to allowmore solar energy to enter the box but does not allow it to flowout in the form of radiant heat.

(c) A plane mirror reflector is used to reflect solar energy into the box.(d) The optimum temperature attained by this cooker is 100°C to 140°C.(e) The two advantages of solar cooker are

(i) the cost of cooking food is zero as solar energy comesfree of cast.

(ii) it can cook from one to four dishes simultaneously.(f) The two limitations of box type solar cooker are:

(i) it cannot cook food at night or when the sky is cloudyduring the day time.

(ii) it cannot be used for making chapatis, frying or baking.5. Briefly describe the construction of a photovoltaic cell. State any

two uses of the cell.Ans. Solar cell or a photovoltaic cell is essentially a very thin sandwich of

n-type and p-type wafer thin semiconductors of silicon, in which isplaced a U-shaped metal grid. The lower end of the sandwich isfixed to a metal base which has a metal lead.


The grid has another lead which can be connected to another solarcell in series. The upper surface of semi conducting sandwich iscoated with anti-reflection coating, a black coating.Uses of photovoltaic cell:(i) It is used for providing electric energy to the satellites and space

probes.(ii) It is used to provide electricity to offshore oil rigs and light houses.

6. (a) State three common uses of wind energy.(b) How is wind energy harnessed in the form of electric energy?

Ans. (a) Three common uses of wind energy are:(i) It is used to draw underground water as in the case of

windmills.(ii) It is used to grind grains as in the case of windmills.(iii) It is used to generate electricity as in the case of electric

wind machines.(b) Electric energy is produced from wind energy by using

windmills. The windmills are conventional in their propeller designwhich employs two or three tapered blades. The shaft of thewindmill is connected to the shaft of armature of the generatorwhen the fast moving wind rotates the blades of windmill, itsshaft rotates the armature inside the generator. The rotatingarmature produces electric current.

Thus, the kinetic energy of wind is converted into electricalenergy.

7. State two advantages and two disadvantages of hydel power.Ans. Two advantages of hydel power are:

(a) The water required for generating hydel power is available freeof cost.


(b) Hydel power stations are pollution free.Two disadvantages of hydel power are:

(i) For running a hydel power station, a vast amount of wateris required.

(ii) The minimum height required to convert stored P.E. ofwater into electrical energy is 34 m between the turbineand free surface of water in reservoir. It involves a massiveinvestment on the construction of dams.

8. How is nuclear energy released by the fission process? How is thisenergy converted into electrical energy?

Ans. Most of the nuclear energy is obtained by nuclear fission. The nucleusof the atoms of uranium or plutonium are split in especially designedmachines called nuclear reactors by slow moving neutrons, when alarge amount of heat energy is produced. This heat energy is utilizedin raising steam. The steam in turn is used to run a turbine, coupledwith electric generator. Thus when the blades of a turbine rotate, theheat energy of steam is converted into electric energy.

9. State two limitations of nuclear power?Ans. (a) The waste products from nuclear power plants are very

dangerous to living beings.(b) The waste products give out radiations which can cause diseases

like cancer, leukemia, etc.10. Answer following questions regarding the biogas plants.

(a) Name the raw materials used in these plants.(b) What type of chemical reaction takes place within the plant?

Define the chemical reaction.(c) What is slurry?(d) State two conditions due to which the slurry change into biogas.(e) Why do we prefer biogas, to burning dry biomass?(f) What is the approximate composition of biogas?

Ans. (a) Animal dung and water are raw materials used in biogas plants.(b) The type of reaction takes place within the biogas plants is

anaerobic fermentation.The fermentation of animal dung which takes place in the absence


of air due to presence of anaerobic bacteria present in animaldung is called anaerobic fermentation.

(c) A mixture of animal dung and water is known as slurry.(d) Slurry changes into biogas in absence of air and in presence of

water.(e) Biogas does not cause any pollution while burning dry biomass

causes a lot of air pollution.(f) Biogas consists of methane (65%), carbon dioxide, hydrogen

and traces of hydrogen sulphide along with water vapour.11. What is polluted air?

(a) How is air polluted by the activities of man?(b) Name five major pollutants in air. State the harm they can cause

to living beings.Ans. When the air contains harmful or undesirable substances generated

by the activities of man in concentrations that interferes with humanhealth, safety or comfort, or injurious to plants and animals, it issaid to be polluted air.(a) Most of the pollution is caused by activities of man:

(i) Burning of coal in thermal power plants for the generationof electricity, reduce throw out huge amount of smokeand ash in the atmosphere.

(ii) Vehicles introduce a large amount of smoke, carbonmonoxide, lead, nitrogen oxides and particulate matter.

(iii) Burning of wood or coal or kerosene oil in not properlydesigned chulha or stove causes air pollution.

(iv) Burning of refuse, especially plastic bags, causes a lot ofair pollution.

(v) Cigarette smoking is the most direct and important sourceof air pollution.

(vi) Pesticides sprayed in fields also cause air pollution.(b) The five major pollutants in air are dust and smoke particles,

carbon monoxide, sulphur dioxide, oxides of nitrogen andchlorofluorocarbons.


The harms caused by various pollutants of air are:(i) Dust and smoke particles: Dust and smoke particles

deposit themselves in the lungs. They can cause seriousrespiratory problems.

(ii) Carbon monoxide: It reacts with the red blood cells toform carboxy haemoglobin and reduce their capacity tocarry oxygen.

(iii) Sulphur dioxide: If it is inhaled, it forms sulphuric acid.This acid can burn mucous membrane of lungs which cancause serious problem. It also causes acid rain which candamage crops, trees and marble buildings like Taj Mahal.

(iv) Oxides of Nitrogen: They get dissolves in water vapourpresent in the air to form nitric acid and cause acid rain.

(v) Chlorofluorocarbons: They are responsible for ozonelayer depletion. Ozone layer prevents the harmfulultraviolet radiations to reach on earth. These radiationscause many diseases like skin cancer in living beings.

12. State one way of reducing air pollution in various activities at home.Ans. In the houses we should use improved ‘chulha’ if we use wood,

coal kerosene oil as a fuel, we must use improved stoves, so thatthe production of smoke and carbon monoxide is minimised.

13. State one way of reducing pollution of air by big industrial units.Ans. In big industrial units like thermal power plants, cement plants, steel

plants, etc, we must provide electric precipitators so that the amountof smoke and ash entering the atmosphere is minimised.Sulphur dioxide and nitrogen dioxide gas can be removed by passingthe gases through water, before getting them into the atmosphere.

14. State two ways of reducing air pollution caused by automobiles.Ans. (a) We must use efficient internal combustion engines in our vehicles,

so that petrol or diesel burns completely without emitting anysmoke.

(b) The harmful gases present in the exhaust should be removedby using catalytic converter.


15. What are fossil fuels?Ans. The remains of organisms that lived on millions of years ago have

changed to form coal and oil. These coal, oil and natural gas arecalled fossil fuels.

16. What type of energy does moving air has?Ans. Moving air has kinetic energy.

17. Where do you find atomic power stations in India?Ans. Atomic power stations in India are:

(a) Kakrapara, near Surat in Gujarat(b) Rawat bhata, near Kota in Rajasthan(c) Tarapur, dist Thane, Maharashtra(d) Kalpakkam, near Madras in Tamil Nadu(e) Narora, dist Bulandshahar, U.P.(f) Kaiga, dist Uttar Kannda, Karnataka

18. Name the device that converts solar energy into electricity.Ans. Solar cell or a photovoltaic cell converts solar energy into electricity.

19. Name four types of energy which can be directly related to solarenergy.

Ans. (a) The solar energy is trapped in the plants in the form of chemicalenergy.

(b) Chemical energy in the food is changed to heat energy andmuscular energy in our bodies.

(c) It is the solar energy that changes into the mechanical energy ofwater.

(d) The chemical energy in the fossil fuels is basically the trappedsolar energy.

20. What are the two limitations in harnessing solar energy?Ans. (a) Solar energy cannot be harnessed during night.

(b) Solar energy cannot be harnessed on a cloudy day.21. Name three traditional uses of solar energy?

Ans. Traditional uses of solar energy are:1. It is used for drying wet clothes.2. It is used for drying grains before storage.3. It is used for food preservation.


22. What are semiconductors? What are the elements used in makingsemiconductors in solar cell?

Ans. The materials whose conductivity is less than conductors but morethan insulators are called semiconductors. Germanium (Ge) andSilicon (Si) are the elements used in making semiconductors in solarcells.

23. What are p – type and n–type semiconductors?Ans. The semiconductors which are doped with boron and have an affinity

to attract electrons are called p – type semiconductors.The semiconductors which are doped with phosphorus and havesurplus of electrons are called n–type semiconductors. They havean excess of electron and hence can donate electrons.

24. What are solar cells and solar panels? What are the main uses ofsolar cells?

Ans. A device which directly converts solar energy into electric energy iscalled solar cell.The group of solar cells connected in a specific pattern to producedesired potential difference and magnitude of current is called solarpanel.Uses of solar cells:1. Solar cells provide electric energy to the satellites and other

space projects.2. Solar cells are used in providing electricity for the street lights

and operating community centre like T.V. and radios wheredirect supply of electricity is neither possible nor commerciallyviable.

3. Solar cells are used to provide electricity to offshore oil rigsand light houses.

4. Solar cells are used for providing electricity to electroniccalculator and wrist watches.

25. Give three differences between box type solar cooker and sphericalreflector type solar cooker.

Ans. Difference between box type solar cooker and spherical reflectortype solar cooker:Box type solar cooker:


1. It does not concentrate solar energy at one point as planereflector is used.

2. The rise in temperature is in the order of 100°C to 140°C.3. It cooks only those kinds of food items which require low heat.

Spherical reflector type solar cooker:1. It concentrates energy at one point as concave reflector is used.2. The rise in temperature is above 500°C.3. It cooks those food materials which require strong heating.

26. State and explain five energy changes taking place in hydro- electricpower station.

Ans. Energy changes taking place in hydro electric power stations are:1. As the water flows into the reservoir from the catchment area,

the kinetic energy of flowing water changes into potential energy.2. As the water is released through control valve, the potential

energy of water is converted into kinetic energy.3. As the water flowing at high speed strikes the blades of turbine,

its kinetic energy changes into rotational kinetic energy of theturbine.

4. As the turbine is coupled to the shaft of the generator, therotational kinetic energy of the turbine changes into rotationalkinetic energy of the armature.

5. As the coil of armature rotates in magnetic field, the rotationalkinetic energy of the armature changes into electric energy inthe coils.

27. Explain how tidal energy is harnessed into electrical energy?Ans. The tides have enormous amount of mechanical energy (potential

energy + kinetic energy). This energy can be used to generateelectricity. The tidal power plants are constructed near the narrowbays, where the water level rises up and then falls down appreciablyduring the tides. During high tides, sea water is allowed to passthrough the dam walls by opening gates. When the level of watertends to fall during low tide, the gates are closed. Thus, the seawater collects behind the dam has potential energy. This stored wateris allowed to fall on the blades of turbine to an electric generator.The kinetic energy of the outgoing water changes into electricalenergy.

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