We must adopt technologies that use alternative sources of energy, which are friendlier to the environment.<\/li>\n<\/ol>\nQuestion 26.
\nWhat are thermal power plants? How do they produce electricity?
\nAnswer:
\nA power generating station in which heat energy produced by burning of a fuel is converted to electric power is called a thermal power plant.<\/p>\n
Fossil fuels are burnt in power stations to heat up water to produce steam. The steam so produced is used to run the turbine, which is connected to a generator. The generator converts the mechanical energy of the turbine into electrical energy.<\/p>\n
Question 27.
\nWhy are thermal power plants set up near coal or oil fields?
\nAnswer:
\nThe transmission of electricity is more efficient than transporting coal or petroleum over the same distance. Therefore, many thermal power plants are set up near coal or oil fields.<\/p>\n
Question 28.
\nWhat is hydel power? How do hydel power stations produce electricity?
\nAnswer:
\nElectric power generated by the conversion of the stored energy of free-falling water into electrical energy is called hydel power or hydroelectric power.<\/p>\n
In order to produce hydel electricity, high-rise dams are constructed on the river to obstruct the flow of water and thereby collect water in larger reservoirs. The water level rises and in this process the kinetic energy of flowing water gets transformed into potential energy.<\/p>\n
The water from the high level in the dam is carried through pipes, to the turbine, installed at the bottom of the dam. The energy of water rotates the turbine, which in turn operates a generator. The generator converts the mechanical energy of the turbine into electrical energy.<\/p>\n
<\/p>\n
Question 29.
\nWhy is hydel power considered a renewable source of energy?
\nAnswer:
\nThe water in the reservoir would be refilled each time it rains. Therefore, we need not have to worry about hydroelectricity sources getting used up the way fossil fuels would. Therefore, hydel energy is a renewable source of energy.<\/p>\n
Question 30.
\nHow is the construction of dams across rivers linked with the production of greenhouse gases?
\nAnswer:
\nThe vegetation that submerged due to construction of dams, rots in anaerobic condition and gives out large amount of methane (CH4<\/sub>) in nature which is a greenhouse gas.<\/p>\nQuestion 34.
\nWhat are the problems associated with construction of big dams?
\nAnswer:
\nThere are many problems associated with the construction of big dams. Dams in general and big dams in particular can be constructed only in a limited number of places, especially in regions covered by hilly terrains. Big dams submerge large areas of agricultural land and human habitation causing economic loss and displacement of people.<\/p>\n
Big dams cause destruction of habitats, disrupt ecological balance in the region. The submerged vegetation rots under anaerobic conditions and gives rise to large amounts of methane, which is also a greenhouse gas. The problem of rehabilitating the displaced people is a huge challenge associated with the construction of big dams.<\/p>\n
Question 32.
\nWhat is biomass? Make a list of some of the sources of biomass.
\nAnswer:
\nAny biological material obtained from living or recently lived organisms is called biomass.
\nSome of the sources of biomass include dead and decaying plants and animals, dung of animals, agricultural crop residues, forest residues, fallen leaves of plants, municipal solid waste, sewage, and vegetable peels.<\/p>\n
<\/p>\n
Question 33.
\nName some fuels obtained from biomass.
\nAnswer:
\nFuels obtained from biomass include firewood, crop residue, biogas, charcoal, etc.<\/p>\n
Question 34.
\nWhat is biomass energy? Give examples of biomass fuels.
\nAnswer:
\nEnergy obtained from biomass materials in the form of fuels or electricity is called biomass energy. Biomass fuels include firewood, cow dung cake, charcoal etc.<\/p>\n
Question 35.
\nWhat can he done to obtain bio-energy using biomass?
\nAnswer:
\nBiomass appears in several forms. The method of harnessing energy from each one of them could be different. Direct burning of these materials generally causes pollution but could be the cheapest form of energy. For example, using wood or dried cow dung cakes as fuel generates a lot of smoke. However, if cow dung is used in biogas plant, clean fuel can be generated.<\/p>\n
In villages, all types of biomass are traditionally burnt directly to produce heat. And if modern methods are used, they can be utilized properly. A number of transportation fuels can be produced from biomass, helping to alleviate demand for petroleum products and improve the greenhouse gas emissions. Ethanol and biodiesel are examples of such bio-fuels.<\/p>\n
Question 36.
\nWhy is biomass energy considered a renewable source of energy?
\nAnswer:
\nBiomass is organic matter that can be quickly replenished unlike coal. Biomass is considered a renewable energy source because its inherent energy comes from the sun and it can be replenished in a relatively short time.<\/p>\n
Question 36.
\nList the advantages of biomass energy.
\nAnswer:
\nThe following are some of the advantages of biomass energy :<\/p>\n
\n- It is a renewable source of energy.<\/li>\n
- It is less polluting compared to fossil fuels. While producing biomass energy, we recycle . wastes, which reduces pollution and the spread of diseases.<\/li>\n
- It can be generated from everyday human and animal wastes, vegetable and agriculture leftovers etc. Therefore, biomass energy helps in cleanliness in villages and cities.<\/li>\n
- It provides manure for agriculture and gardens.<\/li>\n
- Biomass energy is relatively cheaper and reliable.<\/li>\n<\/ol>\n
<\/p>\n
Question 38.
\nList the disadvantages of biomass energy.
\nAnswer:
\nThe following are some of the disadvantages of biomass energy:<\/p>\n
\n- Continuous supply of biomass is required to generate biomass energy.<\/li>\n
- Cost of construction of biogas plant is high.<\/li>\n
- Biogas plant requires space and produces dirty smell.<\/li>\n
- Some of the biomass fuels do not produce much heat on burning.<\/li>\n
- Some biomass fuels produce lot of smoke when they are burnt.<\/li>\n<\/ol>\n
Question 39.
\nWhat is biogas? Explain the principle and working of a biogas plant with a labelled schemati diagram.<\/p>\n
OR<\/p>\n
Explain the structure of a biogas plant and the process of production of fuel in biogas plant.<\/p>\n
OR<\/p>\n
Draw the schematic diagram of gobar gas plant Label the following parts:<\/p>\n
\n- Slurry,<\/li>\n
- Gas outlet.<\/li>\n<\/ol>\n
Answer:
\n
\nA gaseous fuel consisting of a mixture of different gases with methane being its largest constituent and produced by the breakdown of organic matter in the absence of oxygen is called biogas.<\/p>\n
A biogas plant has a dome-like structure built with bricks. Slurry of cow-dung and water is made in the mixing tank from where it is fed into the digester. The digester is a sealed chamber in which there is no oxygen. Anaerobic micro-organisms decompose complex compounds of the slurry.<\/p>\n
This breakdown takes a few days. During breakdown, gases like methane, carbon dioxide, hydrogen and hydrogen sulphide are released. This mixture of gases is called biogas. The biogas is stored in the gas tank above the digester from which they are drawn through pipes for heating or lighting.<\/p>\n
Question 40.
\nWhat is slurry?
\nAnswer:
\nA semi-fluid mixture prepared by mixing cow dung and other organic materials with water is called slurry. It is the starting material for the production of biogas in a biogas plant.<\/p>\n
<\/p>\n
Question 41.
\nWhy is slurry left behind in bio-gas plants considered useful?
\nAnswer:
\nSlurry left behind in biogas plants is used as a manure as it is rich in nitrogenous compounds.<\/p>\n
Question 42.
\nName the major constituent of biogas.
\nAnswer:
\nThe chief constituent of biogas is methane.<\/p>\n
Question 43.
\nState the advantages of biogas.<\/p>\n
OR<\/p>\n
Write the properties of biogas that make it a good fuel.
\nAnswer:
\nThe following are some of the principal advantages of biogas:<\/p>\n
\n- Bio-gas is an excellent fuel as it contains up to 75% methane.<\/li>\n
- It burns without smoke, leaves no residue like ash.<\/li>\n
- Its heating capacity is high. This means, biogas has high calorific value.<\/li>\n
- Bio-gas can be used for both heating and lighting.<\/li>\n
- The slurry left behind is good manure, rich in nitrogen and phosphorus.<\/li>\n
- Production of biogas from bio-waste and sewage material provides a safe and efficient method of waste-disposal.<\/li>\n<\/ol>\n
Question 44.
\nWhat is wind energy? Why is it considered an indirect form of solar energy?
\nAnswer:
\nThe kinetic energy possessed by moving air is called wind energy. The uneven heating of the atmospheric air causes the movement of air on earth by the heat of the sun. Hence wind energy is an indirect form of solar energy.<\/p>\n
Question 45.
\nWhat is a windmill? What are its uses?
\nAnswer:
\nA structure that has parts that are turned around by the wind and used to get certain work done is called a windmill. Windmills can be used to lift water from wells, generate electricity, grind corn etc.<\/p>\n
<\/p>\n
Question 46.
\nWhat type of energy conversion occurs in windmills?
\nAnswer:
\nA windmill converts the kinetic energy of the wind into mechanical or electrical energy.<\/p>\n
Question 47.
\nWhat are wind turbines used for?
\nAnswer:
\nWind turbines are used to harness wind energy for the production of electricity.<\/p>\n
Question 48.
\nWhat should be the range of speed of wind for setting up of windmills?
\nAnswer:
\nWindmills can be set up in places where wind speed is higher than 15 km\/h.<\/p>\n
Question 49.
\nWhat are the limitations in obtaining energy from wind?
\nAnswer:
\nLimitations of wind energy include the following:<\/p>\n
\n- The wind speed should be higher than 15 Km\/h to maintain the required speed of the turbine.<\/li>\n
- Wind energy farms can be established only at those places where wind blows for the greater part of the year.<\/li>\n
- A large area of land is required for establishing wind energy farms.<\/li>\n
- The initial cost of establishing wind energy farms is quite high.<\/li>\n<\/ol>\n
Question 50.
\nHow has the traditional use of wind and water energy been modified for our convenience?
\nAnswer:
\nTraditional use of wind and water energy has been modified in the following ways:
\n1. Water energy:
\nTraditionally, waterfalls were used as a source of potential energy in which water was allowed to fall on the blades of the turbine to produce electrical energy. But waterfalls are fewer in number and therefore dams have been constructed. Now-a-days, hydroelectric power stations produce electricity by harnessing the potential energy of stored water.<\/p>\n
2. Wind energy:
\nEarlier, the windmills were used to harness wind energy to do mechanical work such as lifting or drawing water from a well. But, now-a-days windmills are used to generate electricity. In windmills the rotatory motion of the blades turns the blades: of the turbine to generate electricity.<\/p>\n
Question 51.
\nWhy are we looking at alternative sources of energy?
\nAnswer:
\nOur conventional energy sources are depleting very fast. But, the demand for energy is increasing. Therefore, there is an urgent need to explore alternatives to fossil fuels.<\/p>\n
Our conventional sources of energy are highly polluting. Therefore we need to find alternatives that cause lesser pollution and damage to our environment. Conventional energy sources are non-renewable. There is a need to find energy sources that are renewable.<\/p>\n
<\/p>\n
Question 52.
\nWhy is there a need for harnessing non-conventional sources of energy?
\nAnswer:
\nThere is a need for harnessing non-conventional sources of energy for the following reasons:<\/p>\n
\n- The demand for energy is increasing day by day to meet the basic requirements of our changed life-styles, growing use of machines, and industrialisation in order to improve our living standard.<\/li>\n
- The fossil fuels are non-renewable sources of energy and were formed over millions of years and there are only limited reserves of fossil fuels.<\/li>\n<\/ol>\n
Question 53.
\nWhat is solar energy? Why is the sun considered an inexhaustible source of energy?
\nAnswer:
\nThe radiant energy emitted by the sun in the form of heat and light is called solar energy. The availability of solar energy does not depend on the rate at which we use it. It does not get depleted if we use the energy of the sun more and more. This is why sun is considered an inexhaustible source of energy.<\/p>\n
Question 54.
\nWhat is the source of energy of the sun?
\nAnswer:
\nThe enormous amount of energy of sun is due to nuclear fusion reactions taking place in the interior of the sun. Such reactions are also known as thermonuclear reactions.<\/p>\n
Question 55.
\nHow can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?
\nAnswer:
\nThere are three major ways of harnessing solar energy:<\/p>\n
\n- Collecting and converting radiant energy into heat energy using solar collectors.<\/li>\n
- Conversion of radiant energy into electrical energy using solar cells.<\/li>\n
- The natural conversion of solar energy into biomass, which in turn serves as a source of energy.<\/li>\n<\/ol>\n
Solar energy has several limitations. The devices to harness solar energy cannot be used at night. Many gadgets do not work well on cloudy days. They cannot provide enough intensity to be used in our daily routine.<\/p>\n
These limitations can be overcome by making devices that use low intensity of solar energy and give high intensity of light. We can also store energy in storage batteries and use it during night.<\/p>\n
Question 56.
\nWhat is a solar cooker?
\nAnswer:
\nDevices that use solar energy to cook food are called solar cookers.<\/p>\n
Question 57.
\nName two devices that work using heat energy of the sun.
\nAnswer:
\nTwo of the devices that use solar energy are solar cooker and solar cell.<\/p>\n
<\/p>\n
Question 58.
\nWith the help of a neat, labelled diagram, explain the construction and working of a box type solar cooker.
\nAnswer:
\n
\nA box type cooker consists of a tray, which is called as cooking tray. It is usually covered with a double glass window. It is kept in a metal or fibreglass outer casing and the space between the cooking tray and outer casing is filled with glass wool or thermocol insulation. The cooking tray has a lid, which contains a plane mirror on its inner surface.<\/p>\n
The incoming solar radiation passes directly through the double glass lid and it strikes the blackened cooking pots and the cooking tray. The plane mirror also directs the sun’s radiation into the box. The glass cover transmits short wavelength radiations and is almost opaque to low temperature radiation emitted within the box.<\/p>\n
The glass plate creates green house effect inside the box causing the temperature inside to rise. The cooking tray is insulated on the sides and bottom. The cooking containers (with cover) are generally made of aluminium or stainless steel. The cooking vessels placed in the cooking tray are also painted black on the outer surface so that they also absorb solar radiation directly.<\/p>\n
Question 59.
\nWhat kind of mirror – concave, convex or plain – would be best suited for use in a solar cooker? Why?
\nAnswer:
\nThe type of mirror used in a solar cooker depends on the type of solar cooker. A concave mirror would be best suited for use in a solar cooker designed to create higher temperatures. A concave mirror reflects and focuses the sunlight at a point.<\/p>\n
The temperature at that point increases, which heats and cooks the food, placed at that point. However, a plane mirror is suitable for a box type solar cooker because it reflects all the light falling on it to the desired place.<\/p>\n
Question 60.
\nWhich part of the solar cooker is responsible for greenhouse effect?
\nAnswer:
\nGlass sheet present in the solar cooker is responsible for greenhouse effect.<\/p>\n
<\/p>\n
Question 61.
\nWhat is the role of a plane mirror and a glass sheet in a solar cooker?
\nAnswer:
\n1. Plane mirror:
\nThe plane mirror in a box type solar cooker directs the sun’s rays into the box and thus facilitates cooking.<\/p>\n
2. Glass sheet:
\nThe glass sheet is used to cover the box. It allows sun’s rays to enter into the box but does not allow it to escape. Thus, it traps sun\u2019s heat inside by creating glass house effect. The heat trapped is absorbed inside the box.<\/p>\n
Question 62.
\nWhat are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
\nAnswer:
\nAdvantages of using solar cooker:<\/p>\n
\n- Use of solar cookers does not require any fuel such as cooking gas or kerosene, electricity, coal or wood.<\/li>\n
- Solar cookers work on solar energy, which are available for free.<\/li>\n
- Food cooked in solar cooker is nutritious, as useful nutrients present in food are not denatured because of overheating.<\/li>\n
- Solar cookers are environment-friendly and are safe to use. Solar cookers do not cause any pollution.<\/li>\n<\/ol>\n
Disadvantages of using solar cooker:<\/p>\n
\n- Solar cookers cannot be used in all places, at all times and in all seasons. They can be used only during daytime when the sun is shining brightly.<\/li>\n
- Solar cookers will take longer time to cook food than conventional cooking methods. Cooking is slow.<\/li>\n
- The mirror requires continuous readjustment to direct the sunlight into the box.<\/li>\n<\/ol>\n
Solar cookers are not suitable to be used in Polar regions. They cannot be used during night times. They are not so suitable where nights are longer than days.<\/p>\n
Question 63.
\nWhat is a solar cell? What is the principle on which it works?
\nAnswer:
\nA device that converts solar energy into electrical energy is called a solar cell. A solar cell works on the principle of photovoltaic effect. Photovoltaic effect generates a voltage or an electric current in a material upon exposure to light.<\/p>\n
<\/p>\n
Question 64.
\nWrite the advantages of solar cells.
\nAnswer:
\nThe principal advantages associated with solar cells are that<\/p>\n
\n- They have no moving parts,<\/li>\n
- They require little maintenance and<\/li>\n
- Work quite satisfactorily without a focusing device.<\/li>\n<\/ol>\n
Another advantage is that they can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable.<\/p>\n
Question 65.
\nWhat is the range of voltage developed in a typical solar cell? Where are solar cells commonly used?
\nAnswer:
\nA typical solar cell develops a voltage of 0.5 – 1 V and can produce about 0.7 W of electricity when exposed to the bright Sun. Solar cells are commonly used in traffic signals, for lighting homes, for pumping water etc.<\/p>\n
Question 66.
\nWhere are solar cells commonly used?
\nAnswer:
\nSolar cells are used in many scientific and technological applications. Artificial satellites and space probes use solar cells as the main source of energy. Radio or wireless transmission systems or TV relay stations in remote locations use solar cell panels. Traffic signals, calculators and many toys are fitted with solar cells.<\/p>\n
Question 67.
\nWhat are solar panels? How do they work?
\nAnswer:
\nA solar panel is an assembly of solar cells that can convert light directly into electricity. Solar panels actually comprise many smaller units called photovoltaic cells connected in series. Each such cell converts sunlight into electricity. Many cells linked together make up a solar panel. The voltage developed in these cells of the panel gets added up and delivers enough electricity for practical use.<\/p>\n
Question 68.
\nWhy are solar cells not so popular for common use? Explain.
\nAnswer:
\nSolar cells are highly expensive. Silicon, which is used for making solar cells, is abundant in nature but availability of special grade silicon for making solar cells is limited.<\/p>\n
The entire process of manufacture is still very expensive; silver used for interconnection of the cells in the panel further adds to the cost. This is why solar cells are not so popular for common use.<\/p>\n
<\/p>\n
Question 69.
\nCompare and contrast fossil fuels and the Sun as direct sources of enerev.
\nAnswer:<\/p>\n
\n\n\nFossil fuels<\/td>\n | Energy from the Sun<\/td>\n<\/tr>\n |
\n1. These are exhaustible sources of energy.<\/td>\n | Energy from the Sun is inexhaustible.<\/td>\n<\/tr>\n |
\n2. Exploitation of fossil fuels causes environmental pollution and health hazards.<\/td>\n | Harnessing solar energy does not pose any environmental issues and does not cause health hazards.<\/td>\n<\/tr>\n |
\n3. Fossil fuels take millions of years for their formation.<\/td>\n | Solar energy is readily available and is a direct source of energy.<\/td>\n<\/tr>\n |
\n4. Fossil fuels can be used in all places, in all seasons and at all times.<\/td>\n | Solar energy requires the presence of the sun. Thus, solar energy is not available all the time and in all the places.<\/td>\n<\/tr>\n |
\n5. Fossil fuels are costly.<\/td>\n | Solar energy is completely free.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Question 70. \nHow can enegy be harnessed from the sea in different ways? \nAnswer: \nThe energy from the sea can be harnessed in different forms, which are as follows: \n1. Tidal energy: \nTidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.<\/p>\n 2. Wave energy: \nA wide variety of devices have been developed and employed to trap huge waves near the seashore for rotation of turbine and production of electricity.<\/p>\n 3. Ocean thermal energy: \nThe sun heats the water at the surface of the sea or ocean, while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean thermal energy conversion plants.<\/p>\n Question 71. \nWhat are tides? How are they caused? \nAnswer: \nThe periodic rising and falling of water in the oceans is called tides. Tides are caused by the gravitational interaction between the Earth and the Moon.<\/p>\n <\/p>\n Question 72. \nWhat is tidal energy? How is electricity produced from tidal energy? \nAnswer: \nTidal energy is energy produced from tides. It is a renewable form of energy that converts the natural rise and fall of the tides into electricity.<\/p>\n Question 73. \nWhat is wave energy? How are ocean waves caused? \nAnswer: \nThe energy possessed by the waves in oceans and seas is called wave energy. The waves in oceans and seas are caused by the wind. Uneven heating of the air by the heat of the sun produces wind. Wind blowing over the oceans and seas causes rise and fall of waves.<\/p>\n The mechanical energy (both potential and kinetic energy) possessed by the waves is the ocean energy. Wave energy, also known as ocean wave energy, is a type of ocean-based renewable energy source that uses the power of the waves to generate electricity.<\/p>\n Question 74. \nHow is electricity produced by using energy of the ocean waves? \nAnswer: \nA wide variety of devices have been developed and used to trap wave energy. These devices are installed on the shoreline, near the shore or offshore. They collect the wave energy and use them to rotate turbines and produce electricity.<\/p>\n Question 75. \nList the advantages of wave energy. \nAnswer: \nThe following are some of the advantages of wave energy:<\/p>\n \n- It is an abundant and renewable energy resource as the waves are generated by the wind.<\/li>\n
- Wave energy is practically pollution-free.<\/li>\n
- Wave energy is relatively consistent and predictable as waves can be accurately forecast several days in advance.<\/li>\n<\/ol>\n
<\/p>\n Question 76. \nWhy are wave energy systems more reliable than wind energy systems? \nAnswer: \nFluctuations in wind speed are very high. Therefore, wind energy systems are less reliable. However, the variations in waves are less pronounced. Hence, wave energy systems are more reliable.<\/p>\n Question 77. \nWhat is ocean thermal energy? List two advantages and two disadvantages of ocean thermal energy. \nAnswer: \nThe sun heats the water at the surface of the sea or ocean, while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy and is known as ocean thermal energy. Thus, ocean thermal energy is due to temperature difference at different levels in the ocean. \nThe advantages of ocean thermal energy are:<\/p>\n |