| Fossil fuels<\/b><\/td>\n | Sun<\/b><\/td>\n<\/tr>\n| (i) Non-renewable source of energy.<\/td>\n | (i) Renewable source of energy.<\/td>\n<\/tr>\n | (ii) Cause a lot of air pollution.<\/td>\n | (ii) Pollution-free, doesn\u2019t cause any pollution.<\/td>\n<\/tr>\n | (iii) They will exhaust in future.<\/td>\n | (iii) It is a non-exhaustible source.<\/td>\n<\/tr>\n | (iv) Energy can be tapped throughout the year.<\/td>\n | (iv) Energy cannot be tapped during night and cloudy and rainy days.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n | Question 5 |
| Biomass<\/b><\/td>\n | Hydroelectricity<\/b><\/td>\n<\/tr>\n| (i) Renewable source of energy.<\/td>\n | (i) Renewable source of energy.<\/td>\n<\/tr>\n | (ii) Biomass plants can be installed at any place to produce biomass as energy source.<\/td>\n | (ii) Plants can be installed only at the places where dams can be constructed.<\/td>\n<\/tr>\n | (iii) To collect waste materials is a tough and costly process.<\/td>\n | (iii) Once the plants start to work, it is not difficult to collect water.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n | Question 6\n(a) Limitations of wind energy \n(i) Wind energy farms cannot be established everywhere. The wind energy farms can be established only at those places, where wind blows for most part of the year. \n(ii) The wind required for generating electricity should be strong and steady to maintain the desired level of generation. The minimum wind speed necessary for satisfactory working of the wind generator is about 15 km\/h. This is not always so. \n(iii) The wind energy farms require a large area of land. \n(iv) The setting up of wind energy farms is very expensive. \n(b) Limitations of wave energy : The harnessing of sea-waves energy would be a viable proposition only at those places where sea-waves are very strong. This has constraints of time and location. \n(c) Limitations of tidal energy : \n(i) There are very few sites around the world which are suitable for building tidal dams. \n(ii) The rise and fall of sea-water during high and low tides is not enough to generate electricity on a large scale.<\/h3>\n Question 7\n(a) Renewable sources : The sources of energy which are being produced continuously in nature and are inexhaustible, are called renewable sources of energy. The energy derived from flowing water, wind, tides, ocean waves, or wood are examples of energy from such sources. \nNon-renewable sources : These sources are produced over million of years under special conditions. Once consumed, these are not replaceable for a very long time. Fossil fuels like coal, petroleum and natural gas are non-renewable sources. \n(b) Exhaustible sources are non-renewable sources, while inexhaustible sources are renewable sources. \nYes, the options given in (a) and (b) are the same.<\/h3>\n Question 8\nAn ideal source of energy \nMust give an adequate amount of net energy. \nMust be convenient to use so as to give energy at a steady rate. \nMust be easy to store and transport.<\/h3>\n Question 9\nAdvantages of using solar cooker : \n1. The use of solar cooker for cooking food saves precious fuels like coal, kerosene and LPG. \n2. The use of solar cooker does not produce smoke due to which it does not pollute air. \n3. When food is cooked in solar cooker, its nutrients do not get destroyed. This is because in a solar cooker, food is cooked at a comparatively lower temperature. \n4. In a solar cooker, up to four food items can be cooked at the same time. \nDisadvantages of using solar cooker : \n1. The solar cooker cannot be used to cook food during night because sunshine is not available at that time. \n2. If the day sky is covered with clouds, even then solar cooker cannot be used to cook food. \n3. The direction of reflector of solar cooker has to be changed from time-to-time to keep it facing the sun. \nSources of Energy \n4. The box-type solar cooker cannot be used for baking (making chappattis, etc.) or for frying. \nThe places that receive rain most of the year or where the sky remains cloudy, the solar cooker has limited utility.<\/h3>\n Question 10\nSome of the environmental consequences of the increasing demand for energy are the following : \n1. The combustion of fossil fuels is producing acid rain and damaging plants (crops), soil and aquatic life. \n2. The burning of fossil fuels is increasing the amount of greenhouse gas carbon-dioxide in the atmosphere. It has also affected the rainfall. \n3. The cutting down of trees from the forest for obtaining fire-wood is causing soil erosion and destroying wild life. \n4. The construction of hydro-power plants is disturbing ecological balance. \n5. Nuclear power plants are increasing radioactivity in the environment. \nThe following steps can be taken to reduce energy consumption : \n1. Switch off lights, fans, TV. and other such electrical appliances when not needed, to save electricity. \n2. Use energy efficient electrical appliances to save electricity. This can be done by using compact fluorescent lamps (CFL) and tube lights in place of conventional filament- type electric bulbs. \n3. Good quality stoves should be used to burn fuels like kerosene and LPG so as to obtain maximum heat. \n4. Pressure cookers should be used for cooking food to save fuel. \n5. Solar cookers should be used to cook food whenever possible and solar water heaters should be used to get hot water. \n6. The use of biogas as fuel should be encouraged in rural areas. \n7. Bicycles should be used for short distances to save fuel like petrol which is used in cars, scooters and motorcycles.<\/h3>\n Question 1\nA good source of energy would be one, \ni) Which would do a large amount of work per unit volume or mass. \nii) Be easily accessible. \niii) Be easy to store and transport, and \niv) Perhaps most importantly, be economical.<\/h3>\n Question 2\nA good fuel would be one, \ni) Which is easily available. \nii) It should not produce too much of smoke. \niii) On burning should release less amount of heat.<\/h3>\n Question 3\nSolar energy can be used for heating food because it is easily available, it will not produce smoke and it will not release any amount of heat.<\/h3>\n Question 4\nFossil fuels are non-renewable. Burning of coal or petroleum products causes the air pollution. The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels are acid oxides. These lead to acid rain, which affects water and soil resources.<\/h3>\n Question 5\nThe fossil fuels are non-renewable sources of energy. So we need to conserve them. If we were to continue consuming these sources at such alarming rates, we would soon run out of energy. In order to avoid this, alternate sources of energy were explored.<\/h3>\n Question 6\nThe wind possesses kinetic energy. This energy was harnessed by windmills in the past to do mechanical work. Today, wind energy is also used to generate electricity. \nAnother traditional source of energy was the kinetic energy of flowing water or the potential energy of water at a height. Hydropower plants convert the potential energy of falling water into electricity.<\/h3>\n Question 7\nPlane mirror would be best suited for use in a solar cooker. A plane mirror is used as a reflector. The reflector is used to increase the area over which the solar energy is collected so that more and more heat rays of the sun may enter the solar cooker.<\/h3>\n Question 8\nThe energy from the oceans can be obtained mainly in three forms, \na) Tidal energy \nb) Ocean waves energy \nc) Ocean thermal energy \nThe energy potential from sea is quite large, but efficient commercial exploitation is difficult.<\/h3>\n Question 9\n\u2018Geo\u2019 means \u2018earth\u2019 and \u2018thermal\u2019 means \u2018heat\u2019. Thus the geothermal energy is the heat energy from the hot rock present inside the earth. This heat can be used as a source of energy to produce electricity.<\/h3>\n Question 10\nThe advantages of nuclear energy is as follows, \n(a) It generates electricity. \n(b) Disease like cancer can be treated. \n(c) It helps for the improvement in the agriculture and industry.<\/h3>\n Question 11\nYes, Solar energy does not cause any pollution. Solar cells make use of the \u2018everlasting solar energy\u2019 and their use does not produce any environmental pollution.<\/h3>\n Question 12\nYes, hydrogen is a cleaner fuel than CNG because of its very high colorific value, hydrogen is an extremely good fuel.<\/h3>\n Question 13\nHydro Energy and Solar Energy \nHydro energy or water energy is renewable source of electric energy, which will never get exhausted, since water is available in plenty. \nSolar energy is also known as light energy, which is obtained from the sun and it will never get exhausted.<\/h3>\n Question 14\nCoal and petroleum are the two energy sources that are considered to be exhaustible. They are non-renewable sources of energy and are present in a limited amount in the earth. Once exhausted, they will not be available to us again.<\/h3>\n Question 15\n(a) a sunny day.<\/h3>\n Question 16\n(c) nuclear energy.<\/h3>\n Question 17\n(c) nuclear energy.<\/h3>\n Question 18\nFossil fuels are non-renewable sources of energy. These non-renewable sources of energy (like coal, petroleum, natural gas) are present in a limited amount in the earth. Once exhausted, they will not be available to us again. \nThe sun is the source of all energy. The sun is a renewable source of energy, provides us heat and light energy free of cost. The energy obtained from the sun is called solar energy. The energy coming from the sun contains heat rays, visible light, ultra-violet rays and some gamma rays.<\/h3>\n Question 19\nThe waste material of living things and the dead parts of living things is called bio-mass. Bio-mass contains carbon compounds and it is the oldest source of heat energy for domestic purposes. The important examples of bio-mass being used as a fuel are wood, cattle dung and agriculture wastes like bagasse. \nHydropower plants convert the potential energy of falling water into electricity. Water energy is a renewable source of electric energy, which will never get exhausted. The construction of dams on rivers helps in controlling floods and in irrigation.<\/h3>\n Question 20\na) There are many limitations in harnessing wind energy. Wind energy farms can be established only at those places where wind blows from the greater part of a year. The wind speed should also be higher than 15 Km\/h to maintain the required speed of the turbine. There should be some back-up facilities to take care of the energy needs during a period when there is no wind. \nb) The waves are generated by strong winds blowing across the sea. Wave energy would be a viable proposition only where waves are very strong. \nc) Tidal energy is harnessed by constructing a dam across a narrow opening, the location where such dams can be built are limited.<\/h3>\n Question 21\nThe options given in (a) and (b) are the same. \nThose sources of energy, which are being, produced continuously in nature and are inexhaustible are called renewable sources of energy. \nThose sources of energy, which have accumulated in nature over a very, very long time and cannot be quickly replaced when exhausted are called non-renewable sources of energy.<\/h3>\n Question 22\nThe important qualities of an ideal source of energy is \na) It should be a renewable source of energy. \nb) It should be pollution-free. \nc) It should be economical. \nd) It should be easily accessible.<\/h3>\n Question 23\nThe advantages of a solar cooker \ni) The use of solar cooker for cooking food saves fuel. \nii) The use of solar cooker does not produce smoke due to which the environment also does not get polluted. \niii) When food is cooked in a solar cooker, its nutrients do not get destroyed. This is because in a solar cooker, food is cooked at comparatively lower temperature. \niv) In a solar cooker, upto four food items can be cooked at the same time. \nThe disadvantages of a solar cooker \ni) The box-type solar cooker cannot be used to make chappaties. \nii) The box-type solar cooker cannot be used for \u2018frying\u2019. \nThe limited utility of a solar cooker is \ni)The solar cooker cannot be used to cook the food during nighttime. \nii) If the day-sky is covered with clouds, even then the solar cooker cannot be used to cook the food. \niii) The direction of reflector of solar cooker has to be changed from time to time to keep it facing the sun.<\/h3>\n Question 24\nExploiting any source of energy disturbs the environment in some way or the other. The source we would choose depends on factors such as the case of extracting energy from that source, the economics of extracting energy from the source, the efficiency of technology available and the environmental damage that will be caused by using that source. \nWe cannot depend on the fossil fuels for much longer, if we manage bio-mass by replacing the trees we cut down for fire-wood, we can be assured of a constant supply of energy at a particular rate. Renewable energy is available in our natural environment, in the form of some continuing or repetitive current of energy, or is stored in such large under ground reservoirs that the rate of depletion of reservoirs because of extraction of usable energy is practically negligible.<\/h3>\n Question 1.\n(c) The fossil fuels are non-renewable sources of energy whereas wood, the Sun and wind are renewable sources of energy. Non-renewable sources of energy are those which are exhaustible and cannot be replaced, once they have been used. They are also known as conventional sources of energy.<\/h3>\n Question 2.\n(d) The thermal power plant generates electric power from heat produced by burning fossil fuel, i.e. coal and petroleum. Everyday we burn a large amount of fossil fuels to heat up water to produce steam. The steam so produced runs turbines to generate electricity.<\/h3>\n Question 3.\n(b) In a hydroelectric power plant, more electrical power can be generated, if water falls from a greater height, because the rise in water level causes the increase in potential energy of water. Thus, when it flows from higher position more amount of kinetic energy is formed by the conversion of higher potential energy and this kinetic energy in the form of moving water can produce more electrical power.<\/h3>\n Question 4.\n(c) Wind energy farms can be located only in vast open areas located in favourable wind conditions as the minimum velocity for a windmill to functions is 11-16 km\/h and is called as cut in speed. Thus, the power generated in a windmill depends on wind velocity.<\/h3>\n Question 5.\n(a) The Sun has been radiating an enormous amount of energy at the present rate for nearly 5 billion years and will continue radiating at that rate for about 5 billion years more, so the Sun can be taken as an inexhaustible source of energy.<\/h3>\n Question 6.\n(c) Glass sheet present in the solar cooker easily passes the radiation into the solar cooker and the radiation gets absorbed and that reflected back by the black coating is of longer wavelength and cannot pass back out through the glass. Thus, glass sheet produces greenhouse effect in solar cooker.<\/h3>\n Question 7.\n(b) The water at the surface of the sea or ocean is heated by the Sun, while the water in deeper sections is relatively cold. This difference in temperature between these layers ranges from 10-30 \u00b0C and is exploited to obtain energy. Thus, ocean thermal energy is due to temperature difference at different levels in the ocean.<\/h3>\n Question 8.\n(c) The major hazard of nuclear power generation is the storage and disposal of spent or used fuels. Improper nuclear waste storage and disposal result in environmental contamination as well as risk of accidental leakage of nuclear radiation. It happened in Chernobyl disaster 1986, Fukushima Nuclear disaster 2011 caused great damage to the living beings and habitats.<\/h3>\n","protected":false},"excerpt":{"rendered":" |