5. Towards Green Energy Can you recall? i. What is energy? Ans. The capacity of a body to perform work is called its energy. ii. What are different types of energy? Ans. The different types of energy are potential energy and kinetic energy. iii. What are different forms of energy? Ans. The different forms of energy are: mechanical energy, heat energy, light energy, sound energy and chemical energy. Let’s Discuss • Make a list of the work that we do in our day-to-day life using energy. Which forms of energy do we use to do this work? Discuss with your friends. Ans. i. Heat energy is used to cook food. ii. Electrical energy is used for running electrical appliances such as fan, TV, computer, etc. iii. Sound energy is generated using chemical energy stored in our body while speaking. iv. Kinetic energy is used for running, cycling etc. Energy and use of energy In energy has become a primary need along with food, Cloth and shelter. We need energy in different forms for diverse types of works. The energy that we need may be in the form of mechanical energy chemical energy, sound energy, light energy or heat energy. Make a table • Make a table based on forms of energy and corresponding devices. Ans. Instrument Converts energy form Converts energy to Electric heater Electrical energy Heat energy Loud speaker Electrical energy Sound energy Microphone Sound energy Electrical energy Solar cell Light energy Electrical energy Electric lamp Electrical energy Light energy Generator Mechanical energy Electrical energy Can you tell? (1) Where do we use electrical energy in our day-to-day life? Ans. We use electric energy in various appliances such as bulbs and tubelights. Fans, iron, refrigerator, water pumps, cellphone chargers, television sets, tape recorders and computers. (2) How Electric energy is produced? Ans. Electric energy is produced in the generators. By using the principle of electromagnetic induction, the magnetic field around conducting wires is changed and this creates the potential difference. This results in the formation of electric energy. Generation of electrical energy 1. Production of electricity: (1) Michael Faraday invented the principle of electromagnetic induction. This principle is largely used in generation of electricity. (2) This principle is as follows : A potential difference is generated across the conductor whenever magnetic field around a conductor changes. (3) In two ways the field around a conductor is changed. (a) Keeping the conductor stationary and rotating the magnet. (b) Keeping the magnet stationary and changing the field around the conductor. (4) In both cases there is creation of potential difference across the conductor. (5) The electric generators are based on this principle. They generate the electrical power. (6) In commercial power generation plants ￫ Large generators ￫ Turbine having blades rotates the magnet ￫ Flow of liquid or gas is directed on the turbine blades ￫ The kinetic energy in the flow ￫ Rotates the magnets in the electric generator ￫ electric energy is produced. Electromagnetic Induction (7) There are different types of power generating stations depending upon the type of energy source chat is used to rotate the turbine Steam turbine Schematic of electric generator Flow chart showing generation of electrical energy Thermal energy based electric power station: In thermal energy power plants the steam is used to rotate turbines. Coal is burnt ➝ Heat energy given to water ➝ water heated in a boiler ➝ water converted into steam of very high temperature and pressure ➝ Steam in energy used to rotate turbines ➝ Generator connected to turbines ➝ Electric energy produced. The steam is reused by converting it into water ➝Water recirculated to the boiler. Flow chart showing generation of electrical energy using thermal energy Such power plants are called thermal power plants because thermal energy is used here to generate electrical energy. The chemical energy in the coal is converted into electrical energy gradually through several steps Flow chart showing energy transformation in thermal power plant Let’s think (1) Why is the energy in the coal called chemical energy? Ans. The atoms and molecules present in the coal are formed due to chemical bonds. The energy is stored in chemical bonds. When the coal is burnt, this energy is released. The chemical energy in coal is transformed into thermal energy. (2) Why steam is used to rotate the turbine? Ans. When water is heated, it converts into steam. This steam in under high pressure and temperature. This force of steam rotates the turbines. The same steam is again condensed and converted back into water. The excess heat in turbine again makes this water turn into steam. In this way turbine rotates very effectively due to steam, hence, steam is used to rotate the turbine. Schematics of Thermal : power plant Schematics of Thermal: power plant If you see a thermal power station, you will observe two types of towers there. Compare the schematic of the thermal power station with the block diagram above and you will understand how the boiler, turbine, generator and the condenser are arranged in the power station. After combustion of fuel (here, coal) in the boiler, the emitted gases are released to the atmosphere through very high tower. Once the turbine is rotated using the steam at high temperature and high pressure, steam temperature and pressure decreases. This steam is converted back to water by taking out heat from it (i.e by cooling it) . This is done in the condenser using water in the cooling tower. The water in cooling tower is circulated through the condenser. Heat energy in the steam is given to the water and the steam condenses back to water. The heat absorbed by the water is then released to atmosphere through vapour and heated air through cooling tower. Although, thermal power generation is a major way of electricity generation today, it suffers from certain problems Problems caused due to thermal power plants 1. Air pollution due to burning of coal: Burning of coal results in emission of gases like carbon dioxide, sulphur oxide and nitrogen oxide which are harmful to the health. 2. Along with the emission of gases due to burning of coal, soot particles are also released into the environment. This may cause serious health problems related to the respiratory system. 3. The reserves of fuel used in this method i.e. coal are limited. Therefore, in future, there will be limitations on the availability of the coal. Do you know? Some major thermal power plants in India and their capacity Place State Capacity (MW) Vindhyanagar Madhya Pradesh 4760 Mundra Gujarath 4,620 Mundra Gujarath 4,000 Tamnaar Chhattisagarh 3,400 Chandrapur Maharashtra 3,340 Power plant based on Nuclear Energy (1) The energy released by fission of nuclei of Uranium or Plutonium atoms is used to generate the steam of high temperature and high pressure. Steam turbine is used to rotate the generator in the power plant based on nuclear energy. The turbine is rotated due to the energy in the steam. This further drives the generator to produce electricity. Nuclear power plant (2) Energy in the atoms ➝ nuclear energy ➝ converted into thermal energy ➝ converted into kinetic energy of steam ➝ converted into kinetic energy of turbine ➝ converted into electrical energy. Energy transformation in nuclear power plant (3) Formation of nuclear energy: (1) Upon bombardment by neutrons on atom of Uranium -235, absorption of neutron takes place. It converts Uranium -235 into its isotope Uranium-236. (2) Being extremely unstable, Uranium-236 transforms into Barium and Krypton atoms through a process of fission. This releases three neutrons and 200 Me V energy. (3) Three more Uranium-235 atoms undergo fission due to three neutrons generated in this process. Thus, more fission releases more energy. (4) Thus a chain reaction takes place in which the process of fission of Uranium-235 atoms continues. (5) In this way a controlled chain reaction is carried out to release thermal energy, which in turn is used for generating electric energy. Can you tell? • How does nuclear fission take place? Ans. There are proton and neutron in the nucleus of an atom. During nuclear fission, the nucleus undergoes fission either due to natural radiations or due to bombardment of other neutrons on it. The fission liberates the energy which is known as nuclear energy or atomic energy. Internet is my friend Complete the following table for some important nuclear power plants in India. Place State Capacity(MW) Kudankulam ……………….. ………………. Tarapur ………………… .…………….. Ravatabhata ………………… ………………. Kaiga ……………….. ……………….. Nuclear fission (Chain reaction) Schematic of nuclear power point Advantages of nuclear energy. i) Fossil fuel like Coal is not used in a nuclear Power Plant, Hence air Pollution does not occur. ii) If sufficient nuclear fuel is available it. becomes a good source of electrical energy. Problems of nuclear energy 1. The products after fission of nuclear fuel are also radioactive and emit harmful radiations. The products are called as nuclear waste. How to dispose the nuclear waste safely is a big challenge before the scientists. 2. An accident in nuclear power plant can be very fatal. This is because the accident may result in release of very harmful radiations. Compare • Observe the schematic of thermal power plant and the nuclear plant. Discuss what are the similarities and differences between the two? Ans. Similarities between thermal power plant and nuclear power plant. i. Both have a boiler for heating water. ii. Both consist of a turbine which is used to rotate the generator. iii. Both consist of a generator which generates the electrical energy. iv. Both have a cooling water where the steam is converted back to water v. Both consist of a condenser and pump which help in circulating the water.