SOURCES OF ENERGY Class: 10 (Boys) Sub: PHYSICS NOTES A source of energy is one which can provide adequate amount of energy in a convenient form over a long period of time. All the sources of energy are divided into two main categories- 1. Non-renewable sources of energy- Which cannot be quickly replaced. Eg. Fossil fuels, Nuclear Fuels 2. Renewable sources of energy Which are continuously produced in nature. Eg. Solar energy, Tidal energy Characteristics of a good source of energy are Should do a large amount of work per unit mass. Should be cheap and easily available. Should be easy to store and transport. Should be safe to handle and use. Should not cause environmental pollution. There are a two types of Sources of Energy classified by their popularity and use, Conventional Sources of Energy Non-Conventional Sources of Energy Difference Between Conventional and Non-conventional Sources of Energy Conventional The resources which have been in use for a long time. Non-conventional The resources which are yet in the process of development over the past few years. These resources are exhaustible. These resources are inexhaustible. These resources cause pollution as they emit smoke These resources are usually pollution free. and ash. These resources are very expensive to be maintained, stored and transmitted. Examples- coal, natural gas, petroleum, and water power. Conventional Sources of Energy: Fossil Fuel These resources are less expensive due to local use and can easily be maintained. Examples- solar, biomass, wind, biogas, and tidal, geothermal. Fossil fuels are natural energy sources formed by processes such as decomposition of buried organic matter. The decomposing matter is buried deep underneath the surface over time and is exposed to heat and pressure in the earth s crust for millions of years. Fossil fuels consist mainly of carbon-rich fuels such as coal, petroleum and natural gas.
Fossil fuels are the major source of energy for generating electricity in power plants. Coal: Coal is a complex mixture of compounds of carbon, hydrogen and oxygen and some free carbon and small amounts of nitrogen and Sulphur. It is found in deep coal mines under the surface of earth and is a good fuel as it produces lot of heat on burning. Petroleum: Petroleum is a dark coloured, viscous and foul smelling crude oil. The crude oil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and earth particles and also contains small amounts of other carbon compounds containing oxygen, nitrogen and Sulphur Petroleum on fractional distillation is gives fuels such as petroleum gas(lpg), petrol, diesel, kerosene and fuel oil. Natural gas: Natural gas consists mainly of methane with small quantities of ethane and propane. Natural gas is formed under the earth by the decomposition of vegetable matter lying under water. It is used as domestic and industrial fuel and for generating electricity in thermal power plants. Compressed Natural gas(cng) is being used as a fuel in transport vehicles. Disadvantages of Fossil Fuels: Burning of fossil fuel especially coal releases gases and harmful particles which causes air pollution. The oxides of carbon, nitrogen and Sulphur that are released on burning fossil fuels are acidic oxides, which lead to acid rain and affects water and soil resources. Burning of fossil fuels release large amount of carbon dioxide gas which increases the temperature of the atmosphere and causes global warming (greenhouse effect). Controlling Pollution caused by Fossil Fuel: By fitting the vehicles with catalytic converters. By washing down the smoke and acidic gases by water in a scrubber. By installing electrostatic precipitators in their chimneys. Thermal Power Plant: A thermal power plant is a power generation station which burns fossil fuels like coal, petroleum etc to produce electricity. It does so by utilizing the chemical energy stored in the fuel, burning it and then converting it into mechanical energy. This mechanical energy is utilized to operate an electrical generator to generate electricity. Such thermal power plants are designed on a large scale for continuous operation for years. The device here used to convert the thermal energy released by the fuel to mechanical energy
is called a Turbine. In most of the thermal power plants, the fuel is used to heat water. This water on heating turns to steam which is then pressurized and used to run the turbines. Hydropower Plant: A power plant that produces electricity by using flowing water to rotate a turbine(which drives the generator) is called hydro-power plant(or hydroelectric power plant) The electricity produced by using the energy of falling water is called hydroelectricity. 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 The water from the high level in the dam is carried through pipes, to the turbine at the bottom of the dam Since the water falls down through a large height, it flows very fast. A high pressure jet of fast flowing water pushes on the blades of turbine with a great force and makes the turbine to rotate rapidly which is connected to generator and drives the generator producing electricity. Since the water in the reservoir would be refilled each time it rains- hydropower is a renewable source of energy.
Advantages of Hydroelectricity: Does not produce environmental pollution. It is a renewable source of electric energy. Construction of dams on rivers helps in controlling floods, and in irrigation. Disadvantages of Hydroelectricity: The dams can be constructed only in a limited number of places, preferably in hilly terrains. Large areas of agricultural land and human habitation are to be sacrificed as they get submerged. Large eco-systems are destroyed when submerged under the water in dams. The vegetation which is submerged rots under anaerobic conditions and gives rise to large amounts of methane which is also a green-house gas. It creates the problem of satisfactory rehabilitation of displaced people. Improvements in the Technology for using conventional sources: Bio-Mass Energy: Biomass is organic matter obtained from living or recently living organisms, such as crop residue, animal waste, forest debris, municipal solid waste etc. Some examples of biomass fuels are wood, cow-dung, etc. Wood on burning produces lot of smoke and pollutes the air, so it is converted into a better fuel called charcoal. Charcoal burns without flames, is comparatively smokeless and has a higher heat generation efficiency. Bio-gas: Biogas refers to a mixture of gases produced by the anaerobic decomposition of organic matter such as cow-dung, agricultural waste, municipal waste, plant residue, food waste etc. Biogas consists of methane, carbon dioxide, hydrogen, hydrogen sulphide, and moisture. It is also called as gobar-gas as it is mainly produced from cow-dung. Bio-gas Plant: The biogas plant consists of a dome-like structure. Organic material such as discarded food residue, fats, sludge, cow dung etc. are mixed with water and fed to the digester through the inlet as shown in the figure. The digester is a sealed chamber where anaerobic decomposition of organic matter takes place. After a few days, the organic matter completely decomposes to generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide. These gases are then drawn through pipes from the storage tank above the digester and distributed through decentralization channels to nearby centers for use.
Advantages of Bio-gas: Bio-gas is an excellent fuel as it contains upto 75% methane. It burns without smoke, leaves no residue like ash in wood, charcoal and coal. Its heating capacity is high and very cheap. It is also used for lighting purposes It is helpful in waste disposal and renewable source of energy. It is used in generating electricity. Wind Energy: Wind energy is the energy harnessed from wind. The kinetic energy of wind is converted into mechanical energy. Wind energy is used in wind mills which converts the kinetic energy of the wind into mechanical or electrical energy. The kinetic energy of wind can be used to do mechanical work like lifting water from wells or grinding grains in flour mills It can also be used to rotate the turbines of generators to produce electricity called wind turbines. A single windmill produces only a small amount of electricity. So a large number of wind mills in a large area are coupled together to produce more electricity in wind energy farms. Working: The wind blows on the blades and rotates them. The blades turn a shaft inside the box. The shaft goes into a gear box and starts producing electrical energy. Wind turbines operate at wind speed of about 15 miles an hour. When number of windmills are erected over a large area, in the same location, it is known as a wind energy farm. Eg. Kanyakumari, Tamil Nadu Advantages of wind Energy: It is a renewable source of energy It does not cause pollution The recurring cost is less Wind is not available at all times so back up is essential. It requires a large area of land and establishment cost is very high. A minimum wind speed of 15 km/h is required. High level of maintenance is required as they are exposed to rain, sun, and storm.
Alternative or Non-Conventional Sources of Energy: Solar Energy: It is the energy obtained from the sun in the form of heat and light. It is a renewable energy. Solar Constant: The solar energy reaching unit area at outer edge of the earth s atmosphere exposed perpendicularly to the rays of the sun at the average distance between the Sun and earth is known as the solar constant. The value of solar constant is approx. 1.4 kj per second per square metre or 1.4 kw/m 2. Solar Devices: It is a device which gets heated by using sun s heat energy. Eg. Solar cooker, solar heater and solar cell. Solar Cooker: It is device which is used to cook food by utilizing the heat energy radiated by the sun. It consists of a box made up of heat resistant material. The box is painted black on the inside for efficient absorption of solar radiations. It is covered with a lid of plane glass to allow retention of heat energy. A mirror is attached on the inner surface of the box. In order to cook food, solar cookers are kept in sunshine in the direction of the sun s rays to fall on the mirror. The mirror reflects the sun rays inside the box which increases the temperature of the box, thereby cooking the food placed inside the box. Advantages of Solar cooker: Saves precious fuels like coal, kerosene and LPG. Does not produce smoke due to which it does not pollute air. Nutrients of food does not get destroyed as it is cooked in lower temp. Four food items can be cooked at the same time. Cannot be used in the night time and cannot be used on a cloudy day. Direction of the reflector has to be changed according to sun rays. Cannot be used for baking.
Solar Heater: It consists of a copper pipe painted black on the outer surface and is curled in the form of a coil. The copper coil is fitted in a box as coiled copper pipe increases the surface area for absorption of solar energy. A tank storing cold water is placed above the heater and another tank is connected to the heater for storage and supply of hot water. It works similar to the solar cooker. Solar Cells: Solar cell is a device which converts solar energy directly into electricity. Solar cells are made of special materials called semiconductors such as silicon. When light strikes the solar cell, a certain portion of it is absorbed by the semiconductor material which means that the energy of the absorbed light is transferred to the silicon. This energy loosens the electrons from the atoms in the silicon and allows them to flow freely. This produces direct current(dc) or electricity. A single solar cell can produce only a small amount of electricity, so in order to get more electricity, a large number of solar cells are joined together in series called solar cell panel. Advantages of Solar cells: They have no moving parts, they require little maintenance and work quite satisfactorily without the use of any focusing device. They can be set up in remote and inaccessible hamlets or very sparsely inhabited areas where the laying of a power transmission line may be expensive and not commercially viable. The special grade silicon needed for making solar cells are very expensive. Silver wire used to interconnect solar cells for making solar cell panels is expensive. The entire process of making solar cells is still very expensive and has low efficiency as they can convert only about 25 per cent of the light energy falling on them into electricity. Uses of Solar Cells: For providing electricity in artificial satellites and space probes. For providing electricity to remote, inaccessible and isolated places. For transmission of radio and television programmes in remote areas. For providing electricity to light houses situated in the sea and rigs. For operating traffic signals, watches, calculators and toys.
Energy from the Sea: The energy from the sea can be obtained in three forms: Tidal, Wave and Ocean thermal energy Tidal Energy: Tides are the daily rise and fall of ocean levels relative to coastlines due to the gravitational forces of the moon and the sun on the Earth and also the revolution of the Earth. A large amount of energy is stored in tides which is used as renewable sources of energy to generate electricity. Tidal electricity generation involves the construction of a dam across a narrow opening to the sea. The dam (barrage) allows incoming tidal water during high tides, but does not allow flow out. This causes water to accumulate at a higher level in the coastal basin. When the tide flows out, the level of water in the sea decreases, and the water which was blocked using the dam is released. Thus, as sea-water flows in and out of the tidal barrage during high and low tides, it turns the turbines to generate electricity. Advantages: It does not need any fuel. Waves are predictable. It is available free of cost. It is relatively cheap and easy to maintain. It produces no greenhouse gases or other polluting wastes. Limited sites are suitable for constructing tidal dams. Shipping facility gets affected due to the construction of dams. Construction of dams causes changes in the level of tides, thereby resulting in floods. It is very expensive and needs a wide area. Wave Energy: Ocean waves are caused by winds as they blow across the sea which are powerful source of energy and used to produce electricity. At a wave power station, waves cause the water in the chamber to rise and fall, which means that air is forced in and out of the hole located at the top of the chamber. A turbine placed in this hole is turned by the movement of air rushing in and out. The turbine turns a generator to produce electricity. Advantages: The energy is free-no fuel is needed, no waste is produced. It is not expensive to operate and maintain. A wave power station can produce a lot of energy.
It needs a suitable site where waves are consistently strong. It is less viable for commercial purposes. Ocean Thermal Energy: When sunlight falls on oceans and seas, it causes the temperature of water on the surface to rise, while the temperature at the bottom remains comparatively cooler. This difference in temperature ie the warm surface-water is used to boil volatile liquids such as ammonia. Ammonia gas, thus produced, creates pressure and runs the turbine of the generator and produces electricity. The cold water is pumped up to liquefy the gas which creates a cycle for generating electricity. Power plants can be operated only if there is a temperature difference of 20 0 C between the surface sea water and the sea water at a depth of up to 2 km. Commercial exploitation is difficult. Geothermal Energy: Geothermal energy is the heat energy from hot rocks present inside the earth. The extremely hot rocks present below the surface of earth heat the underground water and turn it into steam. As more and more steam is formed between the rocks, it gets compressed to high pressure. Such a place is known as a hot spot. Sometimes, this heated underground water finds an outlet through which it comes out on the surface of the Earth. Such outlets are known as hot springs. A hole is drilled into the earth up to the hot rocks and a pipe is put into it through which steam comes up. This flow of steam is used to drive the turbines of generators to produce electricity. Advantages: No fuel is needed and energy is free. It does not produce any polluting emissionos and does not contribute to the greenhouse effect. They have a minimal impact on the environment as the power stations are not very large. It is not commercially viable. Hot spots or regions that can generate this energy are limited. Hazardous gases and minerals may emerge, which may be difficult to dispose off.
Nuclear Energy: A physical reaction which involves changes in the nucleus of an atom is called a nuclear reaction. The energy released during a nuclear reaction is called nuclear energy. Nuclear energy can be obtained by two types of nuclear reactions- Nuclear fission and Nuclear fusion. Nuclear Fission: The process in which the heavy nucleus of a radioactive atom(such as uranium, plutonium or thorium) splits up into smaller nuclei when bombarded with low energy neutrons, is called nuclear fission. A tremendous amount of energy is produced and there is a small loss of mass as the mass of the original nucleus is just a little more than the sum of the masses of the individual products. Example- the fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal. It is represented as- 235 U + 1 139 n Fission Ba + 94 Kr + 3 1 n + tremendous amount of energy 92 0 59 36 0 The energy produced during fission reactions is used for generating electricity at nuclear power plants. The nuclear fission reaction can be controlled by using control rods made of boron as it has a property of absorbing neutrons. The highly destructive nuclear(atom) bomb is based on the nuclear fission reaction of uranium-235 or plutonium-239 which were dropped on the Japanese cities of Hiroshima and Nagasaki. Nuclear Power Plant: It is a power plant in which the heat required to make steam and turn turbines is obtained by nuclear reactions and use the nuclear fission reaction to generate electricity. Nuclear power plants consists of nuclear reactors which use uranium rods as fuel and heat is generated by the process of nuclear fission. Neutrons smash into the nucleus of the uranium atoms, which roughly split into half and release energy in the form of heat. Carbon dioxide gas is pumped through the reactor to take the heat away. The hot gas then heats water to form steam. This steam drives the turbines of generators to produce electricity. Nuclear Power Plants in India: Tarapur in Maharashtra Rana Pratap Sagar near Kota in Rajasthan Kalpakkam in Tamil Nadu Narora in Uttar Pradesh Kaprapur in Gujarat Kaiga in Karnataka
Einstein s Mass-Energy Relation: According to Einstein mass and energy are equivalent and are related by- E = mc 2 Where, E is the amount of energy produced if mass m is destroyed, and c is the speed of light(in vacuum) The energy released in nuclear reactions is expressed in the units of electron Volt(eV) or Million electron Volt(MeV) 1 ev = 1.602 x 10-19 joules 1 u = 931MeV ie. 1 atomic mass unit is equivalent to about 931 MeV of energy. Nuclear Fusion: The process in which two nuclei of light elements(hydrogen) combine to form a heavy nucleus(helium), is called nuclear fusion. It is carried out by heating the lighter atoms to extremely high temperatures under extremely high pressure. The loss of mass during the fusion process appears as tremendous amount of energy. It is represented as 2 2 H + H Fusion 3 He + 1 n + Tremendous amount of energy 1 1 2 0 The energy produced during nuclear fusion has not been controlled so far, so it could not be used for generating electricity. Since it takes place at extremely high temperatures, it is also called thermonuclear reactions and it is used for producing a weapon of mass destruction called hydrogen bomb. The sun which gives us heat and light, derives its energy from the fusion of hydrogen nuclei into helium nuclei, which is going on inside it, all the time. Advantages of Nuclear Energy: It produces a large amount of useful energy from a very small amount of a nuclear fuel. Once the nuclear fuel is loaded into the reactor, the nuclear power plant can go on producing electricity for two or three years at a stretch and does not need the refueling again and again. It does not produce gases like carbon dioxide which contribute greenhouse effect or Sulphur dioxide which causes acid rain. It needs huge investments for its construction. Radioactive waste such as used uranium are dangerous hazard to the environment. There is a high risk of accidents by leakage and emission of radiations. It can be used for negative purposes. Environmental consequences of the increasing demand for energy: The combustion of fossil fuel is producing acid rain and damaging plants, soil and aquatic life. The burning of fossil fuel is increasing the amount of greenhouse gas in the atmosphere. The cutting down of trees from the forest for obtaining fire-wood is causing soil erosion and destroying wild life. The construction of hydro-power plants is disturbing ecological balance. Nuclear power plants are increasing radioactivity in the environment.
Factors to be kept in mind while choosing a source of energy: The ease of extracting energy from that source. The cost of extracting energy from the source. The efficiency of technology available to extract energy from that source. The damage to environment which will be caused by using that source. Steps to reduce energy consumption: Switch off lights, fans, TV when not needed to save electricity. Use CFL and tube lights in place of filament bulbs. Good quality stoves should be used to burn fuels like LPG to obtain maximum heat. Pressure cookers should be used for cooking food to save fuel. Solar cookers and heaters should be used whenever possible. Use of biogas should be encouraged in rural areas. Bicycles should be used for travelling short distances. ***********