What are the properties of a good fuel?
A good fuel is the one which can produce
i) large amount of heat
ii) less amount of smoke and
iii) easily available

2. List the properties of a good source of energy
A good source of energy is the one which
i. would do a large amount of work per unit volume or mass
ii. can be easily accessible
iii. can be easily stored and transported and
iv. is economical

3. If you could use any source of energy for heating your food, which one would you use and why?
Good fuel. For reasons refer Qn. No.1

4. What are fossil Fuels? Discuss the advantages and disadvantages of a fossil fuel?
The non – renewable sources of energy which was formed over millions of years ago underground in the form of coal and petroleum are called fossil fuels.
Advantages
Fast growing global demand for energy for industrialization was met by fossil fuels. It can be used for the generation of electricity.
Disadvantages
Burning fuels cause air pollution due to the oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels. As these are acidic oxides, they lead to acid rain which affects our water and soil resources.

5. How has the traditional use of wind and water energy been modified for our convenience?
Wind energy which was used initially for lifting water are now used for generating electricity.
Water energy which was used for transportation before is now a good source to generate electricity.

6. Why are we looking for alternate source of energy?
Because fossil fuels are exhaustible.

7. What measures are to be taken to reduce air pollution caused due to fossil fuel?
Pollution can be reduced by increasing the efficiency of the combustion process and using clean fuel thereby reducing the escape of harmful gases.

8. Brief the basic construction of an electric generator.
The simplest device used for generating electricity has one moving part, a rotor-blade assembly. The moving water or wind or steam acts on the blades to spin it which impart energy to the rotor. This turns the shaft of the dynamo and converts mechanical energy into the electrical energy.

9. How is electricity generated in thermal Power plants?
Fossils fuels are burnt in large amount to heat up water and to produce steam. The steam turns the turbine to generate electricity.
Many thermal power plants are set up near coal or oil fields because transmitting electricity is more efficient than transporting coal and petroleum over the same distance.

10. Write a note on the functioning of hydro power plants
The kinetic energy of flowing water or the potential energy of water at a height is used to rotate the turbine and generate electricity. This energy thus generated is hydel energy.
High – rise dams are constructed on the river to collect water in large reservoirs. The water from high level in the dam is carried through pipes to turbine at the bottom of the dam. The potential energy of the high level water is converted into kinetic energy and used to rotate the turbine to produce electricity.

11. What are the advantages of hydel energy?
It is a renewable source of energy. Huge amount of energy can be harnessed through hydel power plants.

12. What are the limitations in using hydel energy in spite of its huge generation of electricity?
The limitations are
a) Difficulty in building big dams
b) Non – availability of places, hilly terrains to construct dams
c) Large area of land is sacrificed
d) Large eco-systems are destroyed
e) The rotten vegetation under water produces methane a green- house gas
f) Danger to the people living nearby
g) Difficulty in the rehabilitation of the affected.

13. What is meant by bio-mass?
The source of fuels obtained from plant and animal products like wood and cow dung is called bio – mass.

14. What are the disadvantages of using bio-mass as a fuel?
i. They do not produce much heat on burning
ii. Lot of smoke is given out when burned which causes air pollution.

15. How can you obtain charcoal from wood? In what way is it better than wood as a fuel?
When wood is burnt in limited supply of oxygen, water and volatile materials in it get removed, the residue left behind is called charcoal. It is smokeless and has higher heat generation efficiency (calorific value).

16. How is bio gas formed? Name the gases it contains.
The gas produced when cow dung, various plant materials like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen is called bio gas.
Biogas is the combination of gases like methane carbon dioxide, hydrogen and hydrogen sulphide.

17. Explain the construction and working of biogas plant.

18. What are the advantages of using biogas?
– Excellent fuel which burns without smoke and leaving no residue
– High heating capacity
– Also used for lighting
– The slurry left behind is an excellent manure
– Safe and efficient method of waste disposal

19. How is wind energy harnessed?
Kinetic energy of wind is used to generate electricity using windmills. It consists of a large electric fan which is erected at some height. This fan is rotated by the wind which in turn rotates the turbine of an electric generator.

20. What is a wind farm?
A large number of wind mills erected over large area is known as wind energy farm. The energy output of each wind mill is coupled together to get more electricity.

21. What are the advantages of using wind mills to harness energy? What are the difficulties in constructing wind farms?
It is an environment friendly and efficient renewable source. No recurring expenses while using it.
The limitations faced are
a. Windmills can be erected only at those places where wind blows at a minimum speed of 15 km/h
b. Back up facilities are to be made in case of no wind
c. Required a large area of land for establishment
d. Initial cost of establishment is high and a high level of maintenance is required

22. Name some devices used for harnessing solar energy.
Solar heater, solar cooker, solar cell etc.

23. What is the principle behind the working of a solar cooker?
The principles used are black body absorption and green house effect.

24. Explain how a solar cooker is constructed.
A box type solar cooker is made of a non conducting material with thick walls and its inner walls painted black. With the help of a plane mirror hinged on the top of the box, sunlight is reflected into the box. The box is covered with a glass sheet for the retention of heat inside due to green house effect. The range of heat inside is 100 degree Celsius to 140 degree Celsius, if kept for two to three hours. Keeping black containers in the box help us to cook food items that require slow heating. The limitations of using solar cooker are that it can be used only at certain times during a day.

25. What kind of mirror – concave, convex or plain – would be best suited for use in solar cooker? Why?
Concave mirror is used in concentration type solar cookers to focus the heat radiation from sun to a particular point.
Plane mirror is used to reflect light into the box in the box type solar cooker.

26. Write a note on solar cells and its advantages and disadvantages.
Solar cells convert solar energy into electrical energy. It is made up of a material called silicon. Each cell can produce a voltage of 0.5 to 1 V and can produce about 0.7 W of electricity. Arrangement in which a large number of silicon cells are combined to get electricity in high level is called solar panel. They are mounted on specially designed inclined roof tops exposed to the solar radiation.
Advantages
– Need little maintenance and no focusing devices
– Can be useful in remote and inaccessible places where the power transmission is difficult.
Disadvantages
– Availability of special grade silicon is limited
– Manufacturing is expensive as silver is used for interconnecting cells

27. What are the applications of solar cell?
a. Used in artificial satellites and spacecrafts
b. Used in radio or wireless transmission system or TV relay stations
c. Used in traffic signals, calculators and toys

28. What is meant by tidal energy? How is it used to generate electricity?
Due to the gravitational pull of the moon on the earth, the level of water in the sea rises and falls. This phenomenon is called high tide and low tide. The difference in sea level gives tidal energy. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening converts tidal energy into electricity.

29. What is wave energy?
The kinetic energy possessed by huge waves near the seashore can be used to operate the rotor of the generator and electricity is generated.

30. Give the source of ocean thermal energy (OTE). Describe briefly the working of a Ocean Thermal Energy Plant (OTEP)
The water at the surface of the sea is heated more by the sun than that at the deep sea. The difference in temperature is exploited as ocean thermal energy. The ocean thermal energy plants, OTEC, work if this temperature difference is about 20 degree Celsius. The warm surface water is used to boil a volatile liquid like ammonia. This vapor is used to the run the turbine of a generator to get electricity. The cold water from the depth is pumped up to condense the vapor again to liquid ammonia.

31. What are the limitations of the energy that can be obtained from the oceans?
– Initial cost is high.
– No continuous supply of energy
– Difficulty in constructing power plants near the ocean.

32. Identify the terms ‘hot spots’ and ‘hot springs’.
Due geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’.
Hot water from hot spots finds outlets at the surface. Such outlets are known as ‘hot springs’.

33. Explain how geothermal energy can be harnessed. What is the limitation in harnessing it?
34. What are the two processes by which the nuclear energy is released?
Nuclear fission and nuclear fusion

35. How the energy released by nuclear fission is made use of in generating electricity?
The nucleus of a heavy atom such as uranium can be split apart into lighter nuclei. Tremendous energy is released during this process. Nuclear reaction is used to harness this energy. Self sustaining chain reaction of the fuel ( uranium) releases energy in a controlled rate. This energy produces steam by heating water which rotate turbine to generate electricity.
Advantage: The amount of energy released is tremendous. Energy is supplied for a longer period of time from the source.
Disadvantages:
•Improper fuel storage and disposal of nuclear waste results in environmental contamination
•Possibility of risk of accidental leakage of nuclear radiation
•High cost of installation
•Limited availability of fuel.

36. Hydrogen has been used as a rocket fuel. Would you consider it as a cleaner fuel than CNG (Compressed Natural Gas)?
Yes. Because when hydrogen is burnt the byproduct is only water. So it is cleaner fuel compared to CNG.

37. Can any source of energy be pollution free?
No. Although some sources are not producing any by – products causing pollution the construction or assembly of such devices produces some environmental damage. In this sense we can say no source of energy is pollution free.