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Sources of Energy (NCERT SOLUTION)

1) Name four sources of energy you use from morning when you wake up till you reach the school?

Answer: The different forms of energy are as below:
 (i) Heat energy to cook food
 (ii) Electrical energy to lighten the room.
 (iii) Muscular energy to carry bag and to run bicycle
 (iv) Sound energy to call friends.

2) Name the four forms of energy and the sources.

Forms of energy Source of Energy
(i) Heat energy by burning LPG.
(ii) Electricity.(iii) Muscular energy.
(iv) Sound from electric bell.
(i) Petroleum.
(ii) From hydro energy from thermal power station.
(iii) Food material.
(iv) Hydroelectricity or from thermal power plant.

3) Consider the various options we have when we choose a fuel for cooking our food?
Answer:   LPG, solar cooker, kerosene, gobar gas, charcoal, wood, upala, saw dust.

4) What are the criteria you would consider when trying to categorize something as a good fuel?
Criteria: The fuel should be
High energy – yield.
Easily available.
Environment friendly.
Easily transportable.
Low cost.

5) What is a good source of energy?
A good source of energy has following characteristics:
(i) It could do a large amount of work per unit volume or mass.
(ii) It would be easily accessible.
(iii) it would be easy to store and transport.
(iv) It would be economical.

6) What is good fuel?
Answer:   A good fuel has followed characteristics:
(i) It should have high calorific value.
(ii) It should have normal ignition temperature.
(iii) It should not leave more ash and should not produce harmful gases on burning.
(iv) It should be economical and easy to handle.

7) If you could use any source of energy for heating your food, which one would you use and why?
Answer:    I would use renewable and pollution free sources of energy to heat my food. Because, it would not disturb the ecological balance as well as it would be reproduced in nature by cyclic process when it would be used once.
8) What are the disadvantages of fossil fuels?
Answer:    Following are the disadvantages of fossil fuels:
(i) Fossil fuels are formed under the earth’s surface by a long process which takes   million years to form fossil fuel and there are only limited reserves.
(ii) Fossil fuels are non – renewable sources of energy.
(iii) Burning of fossil fuels causes air pollution. The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels cause acid rain and other respiratory problems for human beings.

8) What are the disadvantages of fossil fuels?
Answer:    Following are the disadvantages of fossil fuels:
(i) Fossil fuels are formed under the earth’s surface by a long process which takes million years to form fossil fuel and there are only limited reserves.
(ii) Fossil fuels are non – renewable sources of energy.
(iii) Burning of fossil fuels causes air pollution. The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels cause acid rain and other respiratory problems for human beings.

9) Why are we looking at alternate sources of energy?
Answer: With the progress of technology, the demand of energy is increasing continuously. Our changing life style and use of more machines to do more and more f task easily and rapidly has increased the demand of energy. This demand of energy cannot be fulfilled by using traditional sources of energy. This is why are looking at alternate sources of energy.

10) How has the traditional use of wood and water energy been modify for our convenience?
Answer: Wood and water are traditional sources of energy. From these sources cannot be maintained as it requires enough trees to be planted. Therefore, following modifications are for our convenience: 
(i) Wood is converted into charcoal by destructive distillation of wood which is a better fuel than wood.
         Use of charcoal is also Eco-friendly as it does not produce smoke on burning. It has higher calorific value and leaves lass residue on burning.
(ii) Use of water energy needs the construction of big dams. So these dams are being constructed at limited number of places. To improve the output of water energy, the technology is being developed to increase the efficiency of devices used to convert water energy into electricity.

11) What kind of mirror – concave, convex or plain would be best suited for use in a solar cooker? Why?
Answer:    Concave mirror. Because, concave mirror can focus all the reactions coming from sun properly at a point and causes more heating.

12) What are the limitations of energy obtained from the oceans?
Answer:   The energy potential from ocean is large but efficient commercial exploitation is difficult.

13) What is geothermal energy?
Answer:   The heat from inside earth heats up the water below the surface. This hot water can be used under favorable condition as source of energy. It is called geothermal energy.

14) What is the advantage of nuclear energy?
Answer:   Nuclear energy is a non – conventional source of energy and provides large quantity of usable form of energy. this is one advantage of nuclear energy.

15) Debate the merits and demerits of each sources and select the best source of energy on this basis.
The fossil Fuels: Coal and Oil
(i) Very large amount of energy can be generated cheaply.
(ii) Transporting it from place to place is easy.
(iii) Engines using fossil fuel are very efficient. This means, only a very small amount of energy is lost.
(iv) Fossil fuels are easily obtainable and can be store almost anywhere.
(i)  Fossil fuels are non – renewable. Once used, they are ended permanently.
(ii) The major disadvantage of fossil fuels is that the cause pollution.
(iii) Fossil fuels need to be extracted from the mines. They may cause land – slide, destroying large areas.
Thermal Power
(i) Very large amount of electricity is generated at a place cheaply.
(ii) Transporting coal, oil and gas to the power station easy.
(iii) Power stations run by petroleum gas are very efficient.
(iv) These can b built almost anywhere.
(i) The major drawback of these plants is the pollution caused by burning of fossil fuels.
(ii) Coal based power stations need huge amount of fuel in order to fulfill the demand. This keeps a large are near the power stations, occupied with piles of coal.
(iii) It is a non – renewable source.
Hydroelectric Power
(i) The water required for running these stations involves no cost.
(ii) It is a renewable source.
(iii) There is no pollution by these stations.
(iv) It helps in irrigation for agriculture.
(v) It helps in control of flood.
(i) These power stations can be built only where there is huge supply of water.
(ii) Constructing a dam is very costly.
(iii) It disturbs the neighboring eco – system. It may even destroy inhabited localities near the dam.
Solar Energy
(i) The cost of cooking is nothing since sun’s energy comes free of cost.
(ii) It does not cause pollution.
(i) It will not work during night or in a cloudy day since sufficient sun ways will not be available.
(ii) It is not possible for all, living in a city to have enough open space where to use solar devices.
Solar Cells
(i) These provide a clean, pollution free and environment friendly source of energy.
(ii) These can be used anywhere as a self – generating source of electricity.
(iii) One constructed, there is no further cost of production or maintenance in such devices.
(iv) It is a renewable source.
(i) These cannot work during night or in cloudy weathers.
(ii) Manufacturing a solar cell is very costly.
(iii) Efficient system to store electricity generated by solar cell is not available.
(iv) These produce only direct current (DC). To run the devices which use alternating current (AC), converted are required which cost lot of energy.
(v) These cannot produce large amount of electricity unless the area is big.
(i) Very large amount of energy is obtained in economical way.
(ii) The by – products after fission may be further utilize. [However, scientists are still to find an effective work to do so.
(i) The radioactive materials required for fission error harmful radiations like gamma rays which cause cancer, leukaemia and other genetic disorders.
(ii) In case of an accident, it will explode like a very big nuclear bomb destroying all lives around.
(iii) Radioactive materials are non – bio – degradable. This means waste product will continue to emit harmful radiation for a long time which will affect the living beings. That is why nuclear power plants should be kept under close observation for possible leakages.
Bio – mass
(i) The bio-gas produced from bio – mass is a clean fuel i. e. it does not cause any pollution.
(ii) The remains of bio – mass is very good natural fertilizer.
(iii) It is obtained free of cost.
(iv) It gives a safe method to dispose off wastes.
(v) It has no storage problem.
(i) The process of bio-gas generation is very slow, which reduces its utility for daily uses.
(ii) The amount of bio-gas generated from the biomass produced in a locality is not enough to serve the fuel requirements of that locality.
Wind Energy
(i) It is a renewable source of energy.
(ii) It does not cause air pollution.
(iii) It is very useful in agricultural farms for running the water pumps or grinding machines.
(iv) It can be very useful for small scale industries which do not require high amounts of electricity.
(v) Once constructed, it supplies energy free of cost.
(vi) It is the best source of energy for coastal areas.
(i) The amount of power generated is low.
(ii) It causes noise pollution.
(iii) It disturbs the rainfall pattern of the locality.

16) Can any source of energy be pollution free? Why or why not?
Answer:   Exploiting any source of energy disturbs the environment. So, we can say that any source of energy cannot be pollution free. For example, if we use wood as source of energy it causes ecological imbalance as well as it causes air pollution due to the production of CO2, SO2 and NO2 like harmful gases during burning of wood directly. Even use of solar energy causes excessive trapping of infrared radiation which causes global warming.

17) Hydrogen has been used as rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Answer:    Hydrogen is a cleaner fuel than CNG because of the following reasons:
(i) Hydrogen has high calorific value than CNG.
(ii) CNG is conventional source of energy but H2 is not.
(iii) CNG is green – house gas but H2 is not.
(Iv) Burning of CNG gives out CO and CO2 gases but burning of H2 does not give any such harmful gases.

18) Name two energy sources that you would consider to be renewable. give reasons for your choices.
Answer:   Two renewable sources of energy are:
(i) Hydro energy: Hydro energy is the energy possessed by running water. the running water at high altitude is utilized and unused water is gone to oceans. Due to cyclic process we obtain running water at high altitude again. So hydro energy is a renewable source of energy.
(ii)Wind energy: Wind energy is trapped to perform various activities. The wind energy is caused in atmosphere by natural cyclic process. So it is a renewable source of energy.

19) Give the name of two energy sources that you would consider to be exhaustible. Give reasons or your choices.
Answer:    Coal and petroleum are the two exhaustible sources of energy because even they are reproduced in nature but it takes millions years to be reproduced in nature.

20) Compare and contrast fossil fuels and the sun as source of energy.


Fossil fuels

  1. It is conventional source of energy.
  2. Sun is the ultimate source of all fossil fuels.
  3. Fossil fuels cannot be used un-judiciously because it is limited in quantity.
  4. Fossil fuels can be used as source of energy at any time.
  5. Use of fossil fuel causes air pollution because during burning of fossil fuel harmful gases are evolved.
  6. It costs to buy fossil fuel.
  1. It is non – conventional source of energy.
  2. Sun is the ultimate and final source of energy on earth.
  3. Sun is larger source of energy and can be used at large scale as according to our need.
  4. Solar energy can be used only in day time.
  5. Solar energy is a clean fuel and can be harnessed without causing any pollution.
  6. It is cost free source of energy.           

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