Sources of Energy

VSAQ (1 marks)
Name the two forms of energy usually at our homes?
Ans. Heat and electricity
Exposure to which component of solar radiation could be a health hazard?
And. Ultra violet radiation.
Name two forms in which solar energy manifests itself in oceans?
Ans. Tidal energy and ocean thermal energy
What are the sources of energy in nuclear fission and fusion?
Ans. The disappearance of certain mass ( m) in both the processes, fission and fusion. It appears as energy.
Which radiations of sunlight are used in heating a solar cooker?
Ans. Infra red radiations.
Name any two renewable sources of energy?
Ans. Solar energy and Geo-Thermal energy.

SAQ(2 marks)
Give any two peaceful uses of nuclear energy.
Ans. Nuclear energy can be used:
(i) for generating electricity
(ii) in the treatment of cancer
How is electrical energy obtained from nuclear reactors?
Ans.The large amount of heat produced during nuclear fission is treated to convert into steam. The steam is then used to drive turbines which are connected to electrical generators which convert it into electrical energy.
What is the purpose of glass sheet in solar heating devices?
Ans. Glass sheet has a property that permit the infra-red radiations of short wave length from the sun to get into heating device but does not allow IR radiations of longer wave length to leave the solar heating device.
Why is the use of charcoal discouraged although it is a better fuel than coal?
Ans. Because charcoal is prepared from destructive distillation of wood. So, for this purpose more and more trees would have to be cut down which causes deforestation. It affects the ecological balance of earth.
Can any source of energy be pollution free? Why or why not?
Ans. No source of energy can be perfectly pollution free but biomass energy, hydroenergy, wind energy, geothermal energy and solar energy is almost pollution free. If fossil fuel is allowed to burn in presence of excess of oxygen the pollution produced can be much reduced.

SAQ (3 marks)
If you could use any source energy for heating your food, which one would you use and why?
Ans. Fuel to be used should be easily accessible, should be easy to store and transport and should be economical. If we are in city area, LPG should be used since it does not produce pollution, is easily available and is economical.
In rural area, gobar gas or biogas should be used. It is almost free, has high calorific value and is pollution free. It is also renewable source of energy.
What is Bio-energy?
Ans. Bio-energy is the energy generated by biomass. Energy may be in form of fire, fuel oil, biogas, animal dung alcohol, charcoal or even human excreta. Fuels are derived from bio-mass. It is an indirect source of solar energy and is renewable source of energy.
Hydrogen gas has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG. Why or why not?
Ans. The by-product of hydrogen when used as a fuel and burnt is water while that of CNG are water and carbon dioxide gas. Water is an absolutely harmless by-product, however carbon dioxide in the environment causes green house effect leading to global warming. Hence, hydrogen can be called a cleaner fuel than CNG.
“Only a small part of the solar energy that strikes the upper regions of atmosphere, reaches the surface of the earth”. Discuss?
Ans. When the solar energy falls in the top surface of the atmosphere then some solar energy is reflected back into the space by the atmosphere, and the atmosphere also absorbs a lot of solar energy, for example most of the ultra violet rays are absorbed by the ozone layer. So the solar energy which reaches on the earth’s atmosphere is mainly in the form of heat rays (infrared rays) and visible light, which is a small part of the solar energy.
What is geo-thermal energy? What are its limitations?
Ans. Geo-thermal energy is the heat of the earth and is the naturally occurring thermal energy found within rock formations and the fluids held within those formations. Geo-thermal energy is on of those few sources that do not come directly or indirectly from the solar energy.
Limitations
i) Goe-thermal hot spots are scattered and usually some distance away from the areas that need energy.
ii) The overall power production has lower efficiency (about 15%) as compared to that of fossil fuels (35% to 40%)
iii) Though as a whole geothermal energy is inexhaustible, a single bore has a limited life span of about 10 yrs.
iv) Noise pollution is caused by drilling operations at geo-thermal sites.
LAQ (5marks)
1. What are environment consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Ans. The demand of energy consumption is increasing day to day. Exploiting any source energy may disturb the environment in one-way or other. For example getting energy from fossil fuel may cause lot of pollution in air. Getting energy from nuclear fission may create problem of disposal of nuclear waste.
Steps for reducing energy consumption should be such that we get maximum energy from least fuel. For this:
i. Under the given situation technology utilized should be the best possible. For example. Using smokeless chulhas should be preferred to traditional chulhas.
ii. Energy should be extracted by most economic method under the given situation. Where as energy extraction by solar cells may be useless in big towns due to cost factor, it may be indispensable for artificial satellites.
iii. Wastage of energy should be strictly avoided. Energy saved is equal to energy produced.
iv. Sources of energy should be such that it causes least damage to environment.
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