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Insert Question Under: NCERT Solution of chapter SOURCES OF ENERGY for 120 seconds

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What is a good source of energy?
A good source of energy is one which can produce a lot of heat per unit mass. (II) Can do a large amount of work per unit mas. (III) Can be easily accessible. (IV) Can be transported and stored easily. (V) Is economical. (VI) produces low amount of smoke.
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What is a good fuel?
A good fuel is one that produces a large amount of heat on burning, with less smoke, and is easily available.
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If you could use any source of energy for heating your food, which one would you use and why?
Natural gas can be used for heating and cooking food due to its following qualities: 1. it is a clean source of energy. 2. It does not produce huge amount of smoke on burning. 3. Although it is highly inflammable, it is easy to utilize and transport. 4 And it gives a huge amount of heat on Burning.
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What are the disadvantages of fossil fuels?
The disadvantages of fossil fuels are as follows: (a) Burning of coal and petroleum produces a lot of pollutants which causes air pollution. (b) Fossil fuels release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain. which affects the soil fertility and potable water. (c) Burning of fossil fuels produces gases such as carbon dioxide that causes global Warming.
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Why are we looking at alternate sources of energy?
Fossil fuels, which have been generally utilized by human beings as an energy sources, are non-renewable sources of energy. These sources of energy are limited and cannot replenish individually. They are being consumed at an enormous rate. If this rate of consumption continues, then the fossil fuels would be depleted from the Earth. Therefore, we should conserve the energy sources. Hence, we should look for alternate sources of energy.
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How has the traditional use of wind and water energy been modified for our convenience?
Traditionally, waterfalls were used as a source of potential energy which was converted to electricity using turbines. Since, waterfalls are few in number, a huge amount of water dams have been constructed Nowadays, hydro-dams are used to harness potential energy of stored water. In water dams, water falls from a height on the turbine, which produces electricity. Earlier, windmills were used to harness wind energy to do mechanical work such as lifting/drawing water from a well. But, nowadays, windmills are used to produce electricity. In windmills, the kinetic energy of wind is harnessed and converted into electricity. The rotatory motion of the blades turns the turbine of the electric generator to generate electricity.
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What kind of mirror − concave, convex or plain − would be best suited for use in a solar cooker? Why?
A solar cooker utilizes heat of the sunlight to cook and heat food. In a solar cooker, a mirror is used to reflect and focus sunlight at a point. A concave mirror is generally used in a solar cooker for this purpose. The mirror focuses all the incident sunlight at a point and therefore the temperature at that point increases, thereby cooking and heating of the food placed at that point.
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What are the limitations of the energy that can be obtained from the oceans?
The different forms of energy that can be obtained from the ocean are tidal energy, wave energy, and ocean thermal energy. There are several limitations in order to harness these energies. (i) Tidal energy relies on the relative positioning of the Earth, moon, and the Sun. (ii) High dams are required to be built to convert tidal energy into electricity. (iii) To obtain electricity from wave energy. Very strong waves are needed. (iv) To harness ocean thermal energy efficiently, the difference in the temperature of surface water (hot) and the water at depth (cold) must be 20ºC or more.
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What is geothermal energy?
Geothermal energy is the heat energy of the earth. To generate electricity, geothermal power plants use the heat of the Earth When there are geological changes, the molten rocks present in the core of the earth are pushed to the earth’s crust. This forms regions of hotspot. Steam is generated when the underground water comes in contact with these hot spots forming hot springs. This trapped steam is used to generate electricity in geothermal power plants.
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What are the advantages of nuclear energy?
The advantages of nuclear energy are as follows: (a) A huge amount of energy is produced per unit mass. (b) It does not produce smoke and it is a clean energy. (c) Fission of one atom of uranium produces 10 million times the energy released by burning of one atom of carbon. (d) Fusion of four hydrogen atoms produces a large amount of energy which is approximately equal to 27 MeV.
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Can any source of energy be pollution-free? Why or why not?
No, any source of energy cannot be pollution-free. It is said that solar cells are pollution- free. However, even making them indirectly creates harm to the environment. In the case of nuclear energy, after the fusion reaction, there is no waste generated. t is not completely pollution-free, though. Approximately 107 K temperature is needed to begin the fusion reaction, provided by the fission reactions. The wastes released from fission reactions are very dangerous. Therefore, no source of energy is pollution-free.
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Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Hydrogen gas is cleaner than CNG. CNG is made up of hydrocarbons. Therefore, it has carbon contents. Carbon is a type of CNG pollutant. On the other hand, hydrogen is waste-free. The fusion of hydrogen does not generate any waste. Therefore, hydrogen is cleaner than CNG.
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Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Two renewable sources of energy are as follows: (a) Sun: The energy derived from the Sun is known as solar energy. Solar energy is generated by the fusion of hydrogen into helium, fusion of helium into other heavy elements, etc. A large amount of hydrogen and helium is present in the Sun. Solar energy can therefore be replenished on its own. The Sun has 5 billion more years to burn. Hence, solar energy is a renewable source of energy. (b) Wind: Wind energy is derived from high-speed air blowing. To produce electricity, Wind energy is used by windmills. Air blows because of uneven heating of the Earth. As Earth’s heating l continues indefinitely, wind energy will also be accessible forever.
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Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Two exhaustible energy sources are as follows: (a) Coal: It is generated from dead remains of plants and animals that remain buried under the crust of the earth for millions of years. Production of coal requires millions of years. The demand of coal has been increased by Industrialization. However, coal cannot replenish in a short time. Therefore, coal is a non-renewable or exhaustible source of energy. (b) Wood: It is obtained from forests. Deforestation has led the amount of trees on the Earth to decrease at a faster rate. Growing a forest requires hundreds of years. If deforestation continues at this rate, then there would be no wood left on the Earth. Therefore, wood is an exhaustible source of energy.
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A solar water heater cannot be used to get hot water on (a) a sunny day (b) a cloudy day (c) a hot day (d) a windy day
For heating water, a solar water heater uses solar energy. It requires bright and intense sunlight to function properly. On a cloudy day, the sunlight reflects back in the sky from the clouds and is unable to reach the ground. Therefore, solar energy is not accessible available for the solar heater to work properly. Hence, solar water heater does not function on a cloudy day.
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Which of the following is not an example of a bio-mass energy source? (a) wood (b) gobar gas (c) nuclear energy (d) coal
Bio-mass is a source of energy which is obtained from plant materials and animal waste products. Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atom is bombarded with low-energy neutrons. Therefore, uranium atom divides into two relatively lighter nuclei. This reaction generates an enormous quantity of energy. In nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. This reaction produces a tremendous amount of energy. Therefore, nuclear energy is not an example of bio-mass energy source. Wood is a plant material, gobar gas is formed from animal dung, and coal is a fossil fuel obtained from the buried remains of plants and animals. Hence, these are bio-mass products.
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Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy? (a) Geothermal energy (b) Wind energy (c) Nuclear energy (d) Bio- mass
(c) Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atom is bombarded with low-energy neutrons. Therefore, uranium atom divides into two relatively lighter nuclei. This reaction generates a large amount of energy. In nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. Fission reactions provides the energy needed to fuse the lighter nuclei This reaction produces tremendous amount of energy. These reactions can be carried out in the absence or presence of sunlight. There is no effect of sunlight on these reactions. Therefore, nuclear energy is not ultimately derived from Sun’s energy. Geothermal energy, wind energy, and bio-mass are all ultimately derived from solar energy. Geothermal energy is stored deep within the earth’s crust in the form of heat energy. The heating is triggered by the absorption of atmospheric and oceanic heat. It is the sunlight that heats the atmosphere and oceans. The blowing of winds harnesses wind energy.. The uneven heating of the earth’s surface by the Sun causes wind. Bio-mass is derived from dead plants and animal wastes. Chemical changes happens in these dead plants and animal wastes in the presence of water and sunlight. Therefore bio- mass is indirectly associated to sunlight.
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Compare and contrast fossil fuels and the Sun as direct sources of energy.
Fossil fuels are sources of energy, such as coal and petroleum, obtained from underneath the Earth’s crust. They are directly accessible to human beings for use. Hence, fossil fuels are the direct source of energy. These are limited in amount. These are non-renewable sources of energy because in nature they cannot be replenished. Fossil fuels take millions of years for their formation. If the present fossil fuel of the Earth gets exhausted, its formation will take several years. Fossil fuels are also expensive On the other hand, solar energy is a renewable and direct source of energy. The Sun has been shining for several years and will continue for the next five billion years. Solar energy is available free of cost to all in unlimited amount. It replenishes in the Sun itself.
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Compare and contrast bio-mass and hydro-electricity as sources of energy
Bio-mass and hydro-electricity both are renewable sources of energy. Bio-mass is derived from dead plants and animal wastes. Hence, it is naturally replenished. It is the result of natural processes. Few examples of bio-mass are Wood, gobar gas, etc. Whereas hydro-electricity, is obtained from the potential energy stored in water at a height. Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.
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What are the limitations of extracting energy from − (a) the wind? (b) waves? (c) tides?
Wind energy is harnessed by windmills. One of the constraints of extracting energy from wind is that a windmill requires wind speed of over 15 km/h to produce electricity. Also, a large number of windmills are required, covering a huge area. (a) In order to extract energy from waves, very strong ocean waves are required. (b) Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.
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On what basis would you classify energy sources as (a) renewable and non-renewable? (b) exhaustible and inexhaustible? Are the options given in (a) and (b) the same?
: The source of energy that replenishes in nature is known as a renewable source of energy. Few examples of renewable sources of energy are Sun, wind, moving water, bio-mass, etc. The source of energy that does not replenish in nature is known as non-renewable source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non- renewable sources of energy. (a) Exhaustible sources are those sources of energy, which will deplete and exhaust after a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy. Inexhaustible resources of energy are those sources, which will not exhaust in future. These are unlimited. Bio-mass is one of the inexhaustible sources of energy. Yes, the options given in (a) and (b) are the same.
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What are the qualities of an ideal source of energy?
An ideal source of energy must be: I. Economical II. Easily accessible III. Smoke and pollution free IV. Easy to store and transport V. Able to produce an enormous amount of heat and energy on burning
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What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean renewable source of energy. It is free for all and available in unlimited amount. Therefore, operating a solar cooker is not expensive. Disadvantage of a solar cooker is that it is very expensive. It doesn’t operate without sunlight. Hence, on a cloudy day, it becomes ineffective. The places where the days are very short or places with cloud covers round the year, have limited utility for solar cooker.
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What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Industrialization increases the demand for energy. Fossil fuels are easily accessible severe effect on the environment. Too much exploitation of fossil fuels increases the level of greenhouse gas content in the atmosphere, resulting in global warming and a rise in the sea level. The consumption of fossil fuel cannot be entirely reduced. However, some measures can be taken such as using electrical appliances and not wasting electricity. Unnecessary usage of water should be avoided. Public transport system with mass transit must be adopted on a large scale. These small measures can assist to reduce the consumption and conservation of natural resources.
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