Sources of Energy

IMPORTANT NOTES

1. Energy plays a vital role in all walks of life. For example, heat energy is essential for cooking our food and electrical energy is essential for lighting, running machines and factories.

2. Any substance which is available easily and burns in air at moderate rate, producing large amount of heat energy, without leaving behind any undesirable residue, is called fuel.

3. The sources of energy, which have accumulated in nature over a period of hundreds of million years, such that they cannot be replaced when exhausted, are called non-renewable sources of energy.

4. The non-renewable sources of energy are fossil fuels, such as, coal, petroleum and natural gas.

5. The sources of energy, which are being continuously produced in nature and are virtually inexhaustible are called renewable sources of energy.

6. The main renewable sources of energy are: Solar energy, wind energy, hydroenergy, biofuels (fuels from biomass, such as wood and biogas). Energy from oceans geothermal energy.

7. The fuels which are preserved under the Earth’s crust as remains of plants and animals are called fossil fuels. Coal, petroleum and natural gas are examples of fossil fuel.

8. Fossil fuels are very precious. We must use them, when absolutely necessary. Otherwise, they will get exhausted in another hundred years or so, thereby causing unprecedented energy crisis, from which our world will never recover.

9. These days coal is extensively used in generating electric energy at the thermal stations or thermal power house.

10. Natural gas is also used for generating thermal electricity. It is also used as household fuel and the fuel for CNG buses.

11. Petroleum is refined into products such as petrol, diesel, kerosene oil, lubricating oil, furnace oil and petroleum gas.

12. All fossil fuels on burning produce large amount of carbon dioxide gas, small amounts of sulphur dioxide gas and nitrogen dioxide gas. The carbon dioxide gas produces greenhouse effect, which in turn results in global warming. Sulphur dioxide gas and nitrogen dioxide gas, in addition to producing respiratory problems cause acid rain. The acid rain affects our soil, water and forest resources.

13. A hydroelectric power plant is an arrangement in which kinetic energy of flowing water is transformed into electric energy. The electric energy so generated is called hydroelectric energy. Potential Kinetic Kinetic Kinetic energy of energy of energy of energy water flowing rotating generated stored water turbine in in dam generator Conversion of hydel energy into electric energy

14. Water stored in hydroelectric dams is gradually used throughout the year. As the dam gets periodically refilled when it rains, therefore, hydroenergy is a renewable source of energy.

15. Firewood and waste materials produced by the living beings and the dead materials of living beings are collectively called biomass.

16. Amongst the waste materials of the living beings, the dung and excreta from the animals constitute the biomass. Amongst the dead materials of living beings, firewood, the leaves shed by the trees, dry grasses and crop residues constitute biomass.

17. Biogas is a mixture of gases formed when the slurry of animal dung and water is allowed to ferment in the absence of oxygen (or air). The fermentation of animal dung that takes place in the absence of air due to the presence of anaerobic bacteria present in animal dung is called anaerobic fermentation.

18. The biogas is a mixture of methane, carbon dioxide, hydrogen and traces of hydrogen sulphide, along with water vapour. The chief constituent of biogas is methane gas and is about 65% by volume.

19. Moving air is called wind. Winds are formed due to uneven heating of land mass and oceans. In addition, rotation of the earth and local conditions such as presence of mountains, deserts, seas, lakes, etc., also help in the formation of winds.

20. Moving wind has large amount of kinetic energy. This energy was traditionally used by sailors and fisherman to propel their boats. The same kinetic energy was used to run windmills.

21. The energy radiated out by the sun in the form of electromagnetic waves is called solar energy.

22. The amount of energy reaching perpendicularly per square metre per second in the outermost boundary of earth’s atmosphere is called solar constant. The approximate value of solar constant is 1.4 kilojoules per square metre per second.

23. A greenhouse is a house-like structure whose roof as well as walls are made of sheets of glass. It is used in very cold countries to grow vegetables and flowers in winter. As the green plants grow within the glass house, it is called greenhouse and the phenomenon is called greenhouse effect.

24. A device which directly converts solar energy into electric energy is called Solar Cell. Photovoltaic Effect: The phenomenon due to which light energy directly changes into electric energy, when light is incident on certain sensitive materials, is called Photovoltaic Effect.

25. The group of solar cells connected in specific pattern to produce desired potential difference and magnitude of current is called Solar Panel.

26. The solar cell is also called photovoltaic cell. The term photo stands for light and voltaic stands for generation of potential difference. Thus, a photovoltaic cell is a device which converts light energy into electric energy due to the generation of potential difference.

27. During tides an enormous amount of water in the sea rises up through a good height and then falls down. The tides have enormous amount of mechanical energy (potential energy + kinetic energy). This energy can be used to generate electricity.

28. Nuclear energy is generated by two methods. The basic principle is that when a heavy nucleus of elements such as uranium, thorium or plutonium is split or when the lighter elements such as hydrogen or deuterium is fused to form heavy element, such that the total mass of products is less than that of participating atoms, then the difference in mass is converted into energy. The energy released is given by famous equation E = mc^2, first derived by Albert Einstein in 1905.