Quick Review CH –14 Sources of Energy

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CH –14 Sources of Energy

       Class X 

Sources of energy: Different forms of energy, conventional and non-conventional sources of energy: fossil fuels, solar energy; biogas; wind, water, and tidal energy; nuclear energy. Renewable versus non-renewable sources.

1. A good fuel is one that emits large amounts of heat upon burning, produces no smoke, and is readily available.
2. A good source of energy is one that can do a large work per unit volume or mass and can be easily accessible, easy to store and transport.
3. Two fossil fuels - coal and petroleum. Made millions of years ago and there are only limited reserves. We need to conserve fossil fuels because they are non-renewable sources of energy. If we continue to consume these sources, we will soon run out of energy. Alternative sources of energy were discovered to avoid this.
4. Disadvantages of the burning of fossil fuels - Burning of fossil fuels like coal or petroleum products causes air pollution which causes the greenhouse effect of gases like carbon dioxide. Oxides of carbon, nitrogen, and sulfur are released into the air by burning fossil fuels which are acidic oxides and lead to acid rain. Acid rain affects our water and soil resources.
5. The pollution caused by burning fossil fuels can be reduced by using various techniques to increase the efficiency of the combustion of fossil fuels and to reduce the production of various gases and surrounding harmful gases.
6. Flow chart to demonstrate the process of thermoelectric production –Turbines have one moving part, a rotor-blade assembly →The moving fluid acts on the blades to spin them and impart energy to the rotor →The rotor blade, with a speed which would turn the shaft of the dynamo and convert the mechanical energy into electrical energy.
7. Thermal power plant – Fuel is used in thermal power plants to produce large amounts of heat energy which is converted into electrical energy.
8. Hydropower plant – In hydropower plants, the potential energy of water at high altitude and the kinetic energy of flowing water is used to make electricity. Hydropower plants convert the potential energy of falling water into electricity.
9. Advantages of hydroelectricity-
   (i) It is a renewable source.
   (ii) It does not cause any pollution in the environment.
   (iii) The dams constructed over rivers help in irrigation and control of floods.
10. Disadvantages of constructions of dams - Constructions of big dams have certain problems.
    . Large areas of agricultural land or large eco-systems are destroyed when they submerge underwater.
    . The vegetation, which is submerged, decomposes due to anaerobic conditions and gives rise to large amounts of methane gas which is a greenhouse gas.
    . This creates problems in the human habitation of the displaced.
11. Biomass – Wood and cow dung are used for fuels which are plant and animal products, the source of these fuels is called bio-mass.
12. When wood is burnt in a limited supply of oxygen, the water, and volatile substances present in it are removed and the charcoal remains behind as residue. Charcoal burns without flames are smokeless and have high heat generation capacity.
13. Biogas- In the absence of oxygen crop residues, sewage and vegetable waste are decomposed by anaerobic microorganisms into a digester tank to deliver bio-gas,. The starting material is mainly cow-dung, hence it is known as gobar-gas.
14. Preparation of biogas - The plant has a dome-like structure of bricks. Cow-dung and water solutions are mixed in a tank from where it is poured into the digester which is a sealed chamber that does not contain oxygen. Microorganisms decompose a complex compound of the cow-dung solution by anaerobic respiration that takes some days to produce gases such as methane, carbon dioxide, hydrogen, and hydrogen sulfide in the dissolved process. Biogas is stored in a gas tank that is present above the digester and is then drawn through a pipe for use. Phosphorous and nitrogen are the major components present in the leftover slurry of a biogas plant.
15. Useful of biogas -Biogas is excellent fuel, it contains up to 75% methane. It burns without smoke, leaving no residue like ash. Biogas is used for lighting, its heating capacity is very large. The solution left behind is used as an excellent compost rich in nitrogen and phosphorus.
16. Solar cookers and solar water heaters have a dark black color inside them because a black surface absorbs more heat than a white. Some solar cookers produce a high temperature using a mirror to focus the sun's rays.
17. Solar panel - Solar panel is a device that is a collection of solar cells and is used to absorb the sun's rays and convert them into electricity or heat. The two elements of silver and silicon are used to fabricate and manufacture a solar cell.
18. The advantages of the solar panel are that they do not have moving parts, require very little maintenance and work very satisfactorily without the use of any focusing device, they can be installed in remote and inaccessible settlements or in very sparsely populated areas in which laying of power transmission lines can be costly and not commercially viable.
19. Limitation of solar cells- 
    The cost of a solar cell is high. 
    These devices are useful only at certain times during the day.
20. Limitation of solar energy- 
    The efficiency of conversion of solar energy to electricity is low
    It produces d.c. electricity which cannot be directly supplied for household purposes.
21. Silicon is used to make solar cells, it is abundant in nature and the availability of this silicon to make solar cells is limited.
22. The uneven heating of landmines and water bodies by solar radiation generates wind speeds and blows the winds. This kinetic energy of the wind can be used to do work. This energy was controlled by wind energy to perform mechanical tasks.
23. Wind power farm - To generate electricity, the rotational speed of the windmill is used to turn on the turbine of the electric generator. The production of a single windmill is so small and cannot be used for commercial purposes. To get more energy, many windmills are arranged over a large area, known as a wind power farm. The energy output of each windmill is gathered together on a farm to obtain electricity on a commercial scale.
24. Tidal Energy - Due to the gravitational pull of the Moon on Earth, the water level in the sea rises and falls. This phenomenon is called high and low tide and the difference in sea level gives the energy of tides.
25. Tidal energy is controlled by building a dam across a narrow opening into the sea. A turbine is fixed at the opening of the dam and converts tidal energy into electricity.
26. Ocean Thermal Energy - Water at the surface of the sea or ocean is heated by the sun, while at depth the water is relatively cold. This difference in temperature is used to obtain energy in ocean-thermal-energy conversion plants. Hot surface-water is used to boil ammonia which is a volatile liquid. The vapor of this liquid is used to drive a generator's turbine. Coldwater is pumped from the depths of the ocean and condenses the vapor again into a liquid. Energy efficiencies from the ocean such as tidal energy, wave energy, and ocean thermal energy are large, but efficient commercial exploitation is difficult.
27. Ocean-thermal-energy conversion plants can work if the difference between the temperature at the surface water and the water at depth is 2km 20°C or more.
28. Nuclear fusion- Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles and this reaction is responsible for large energy produced in the sun.
29. Nuclear fission - When the nucleus of a heavy atom, such as uranium, thorium, or plutonium, is bombarded with low-energy neutrons, it splits into lighter nuclei and a tremendous amount of energy is released. This process is known as nuclear fission.
30. Hot spot - During geological changes, molten rocks form in deep warm regions of the Earth's crust and are pushed upward and trapped in some areas known as 'hot spots'.
31. Hot spring - When underground water comes into contact with a hot spot, steam is produced. The hot water of that area finds an outlet on the surface. Such outlets are known as hot springs.