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Q No. 4: Compare and contrast fossil fuels and the Sun as direct sources of energy.
Ans: Coal and petroleum are fossil fuels they are obtained from deep under Earth’s crust. They are directly available to human beings for use. Therefore fossil fuels are the direct source of energy. But these are limited in amount also they are non-renewable.
Solar energy is also a direct source of energy. But it is renewable source of energy. The Sun has been shining for several years and will continue billions of years more. Solar energy is available free of cost to all in unlimited amount.
Q No. 5: Compare and contrast bio-mass and hydro electricity as sources of energy.
Ans: Bio-mass is renewable sources of energy. It mass is derived from dead plants and animal wastes. Therefore it is naturally replenished. Wood, gobar gas, etc. are some of the examples of bio-mass.
Hydro-electricity is also renewable sources of energy. But it is obtained from the potential energy stored in water at a height. Energy from it can be produced again and again.
Q No. 8: What are the qualities of an ideal source of energy?
Ans: An ideal source of energy must be:
(a) Cheap in cost
(b) Easily available
(c) Produces less or no smoke
(d) Have high calorific value.
(e) Easy to carry and store
Q No. 9: What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Ans: Solar cooker uses solar energy to heat and cook food. It is renewable source of energy. It is available in unlimited amount for free. Therefore operating a solar cooker is not expensive.
Disadvantage of a solar cooker is that manufacturing cost of a solar cooker is very expensive. If there is no sunlight then it will not work.
There are some places where the days are too short or cloud covers them round the year. There solar cooker cannot be used.
Q No. 10: What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Ans: The demand of energy is increased due to the industrialisation all over the world. Their energy demands are fulfilled by energy obtained from fossil fuels. The burning of fossil fuels causes air pollution and releases large amount of carbon dioxide which results in global warming. So we should use these resources in optimum. We should not waste the energy. We should use alternate source of energy such as solar energy.
Intext Q No.s page no. 243
Q No. 1: What is a good source of energy?
Ans: The characteristics of good source of energy are
(a) It should have high calorific value.
(b) It should be easy to handle.
(c) It is should be easily available.
(d) It is easy to store.
(e) It should be cheaper.
(f)It should produce less amount of smoke.
Q No. 2:What is a good fuel?
Ans: A fuel is said to be good fuel if it produces a large amount of heat on burning without producing a lot of smoke, and is easily available.
Q No. 3: If you could use any source of energy for heating your food, which one would you use and why?
Ans: Natural gas can be used for heating and cooking food as it is a clean source of energy. It has high calorific value also It does not produce a large amount of smoke on burning. It is easy to use and easy to transport.
Intext Q No.s page no. 248
Q No. 1: What are the disadvantages of fossil fuels?
Ans: The disadvantages of fossil fuels are as follows:
(a) Burning of fossil fuels produces oxides of carbon, nitrogen, sulphur, etc. that cause acid rain, which affects the soil fertility and water.
(b) Burning of fossil fuels produce gases such as carbon dioxide that causes global warming.
Q No. 2: Why are we looking at alternate sources of energy?
Ans: Fossil fuels which are traditionally used by human beings everywhere as an energy sources are non-renewable sources of energy. These sources of energy are limited and will disappear after some time. They are being consumed at a large rate. Therefore, we should conserve the energy sources. Hence, we should look for alternate sources of energy.
Q No. 3: How has the traditional use of wind and water energy been modified for our convenience?
Ans: Traditionally, waterfalls were used as a source of potential energy in which water is allowed to fall on the blades of the turbine where the rotatory motion of the blades of the turbine is converted into electrical energy. But waterfalls are few in number therefore water dams have been constructed. Nowadays, hydro-electric power stations are used in order to harness potential energy of stored water.
Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting or drawing water from a well. But now a day’s windmills are used to generate electricity. In windmills the rotatory motion of the blades turns the blades of turbine to generate electricity.
Intext Q No.s page no. 253
Q No. 1: What kind of mirror − concave, convex or plain − would be best suited for use in a solar cooker? Why?
Ans: A concave mirror would be best suited for use in a solar cooker because it reflect and focus the sunlight at a point. The temperature at that point increases which heats and cooks the food placed at that point.
Q No. 2: What are the limitations of the energy that can be obtained from the oceans?
Ans: Tidal energy, wave energy, and ocean thermal energy are various forms of energy that can be obtained from the sun. But there are several limitations to harness these energies. Those limitations are
(i) High dams are required to be built to convert tidal energy into electricity which incurs lot of cost.
(ii) Very strong waves are required, which are not possible all the time.
(iii) Tidal energy depends on the relative positioning of the Earth, moon, and the Sun.
(iv) To harness ocean thermal energy the difference in the temperature of surface hot water and the cold water at depth must be 20ºC or more.
Q No. 3: What is geothermal energy?
Ans: Geothermal energy is generated at the geothermal power plants where the heat of earth is used to generate electricity.
Due to some geological changes, the molten rocks present in the core of the earth are pushed to the earth’s crust. Steam is generated when the underground water comes in contact with these points forming hot springs. This trapped steam is used to generate electricity in the geothermal power plants.
Q No. 4: What are the advantages of nuclear energy?
Ans: The advantages of nuclear energy are as follows:
(a) Large amount of energy is produced per unit mass.
(b) Fission of one atom of uranium produces ten million times the energy released by burning of one atom of carbon.
(c) It does not produce smoke. It is a clean energy.
Q No. 1: Can any source of energy be pollution-free? Why or why not?
Ans: No source of energy can be pollution-free. Every source of energy has some type of pollution. For example the wastes of nuclear reaction are very dangerous to the environment.
Q No. 2: Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Ans: No doubt hydrogen gas is cleaner fuel than CNG as CNG contains hydrocarbons. Which contain carbon and it is a form of pollutant present in CNG. But hydrogen is waste-free. The fusion of hydrogen does not produce any waste. Therefore hydrogen is cleaner than CNG.
Q No. 1: Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Ans: Two renewable sources of energy are as follows:
(a) Sun: The energy derived from the Sun is known as solar energy. Solar energy is produced by the fusion of hydrogen into helium, fusion of helium into other heavy elements, and so on. A large amount of hydrogen and helium is present in the Sun. The Sun has billions years more to burn. Therefore solar energy is a renewable source of energy.
(b) Wind: Wind energy is derived from fast blowing air. Wind energy is harnessed by windmills in order to generate electricity. Air blows because of uneven heating of the Earth. Since the heating of the Earth will continue forever therefore wind energy will also be available forever.
Q No. 2: Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Ans: Two exhaustible energy sources are as follows:
(a) Coal: It is produced from dead remains of plants and animals that buried under the earth’s crust for millions of years ago. It takes millions of years to produce coal. It means coal cannot replenish within a short period of time. So it is a non-renewable or exhaustible source of energy.
(b) Wood: It is obtained from forests. Forests are decreasing at very fast rate due to deforestation. If deforestation is continued at this rate, then there would be no wood left on the Earth. Hence, wood is an exhaustible source of energy.
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