These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 6 Notes – Sources of Energy act as excellent revision resources, particularly in preparation for board exams.
Sources of Energy Class 8 DAV Notes
→ Fuel: A substance which produces heat on burning in air is called a fuel.
→ Classification of Sources of Energy
1. On the basis of occurrence:
- Natural Sources: Sources which are taken from nature, e.g. solar energy, wind energy, hydro energy, etc.
- Synthetic Sources: Sources which are made by man, e.g. batteries.
2. On the basis of physical state
- Solid: Firewood, charcoal, coal, etc.
- Liquid: Kerosene, diesel, petrol, etc.
- Gas: LPG and CNG
3. On the basis of availability
(a) Renewable: A source of energy which can be used over and over again is called renewable source of energy. These are also called inexhaustible source of energy, e.g. wind, sun, biomass and hydropower.
(b) Non-renewable: A source of energy which gets used up and cannot be recreated in a short period of time is called non-renewable source of energy. These are also called exhaustible source of energy, e.g. fossil fuels.
→ Fossil Fuels: The fuels which were formed from dead remains of plants and animals are called fossil fuels. They were formed over a period of millions of years, by the action of heat and pressure under the earth. Coal and petroleum are fossil fuels.
→ Wood: Wood is often used as fuel. This fuel is extracted from biomass. On burning, wood produces heat, carbon dioxide and carbon monoxide.
→ Petroleum: Petroleum is a dark coloured, viscous and foul smelling liquid. This is commonly called crude oil. It is formed during the process of rock formations in the earth.
→ Occurrence of Petroleum: Petroleum is found at a moderate depth (500 m to 2,000 m) between the two layers of impervious rocks. Natural gas is found above petroleum, trapped between the rock and petroleum layer.
→ Drilling of Oil wells: Petroleum is extracted by drilling oil wells.
→ Refining of petroleum: Petroleum is a mixture of various compounds. These are separated through a process called fractional distillation. The process is also called petroleum refining.
→ Natural Gas: Natural gas is found along with petroleum in oil wells. It is used as fuel in industries and in homes. It is also used as automobile fuel.
→ Cleaner Fuel: Fossil fuels produce harmful gases on burning. This is creating environmental pollution. Due to increased level of pollution, it has become important to search for cleaner fuel to save the environment. LPG and CNG are cleaner fuel as they produce lesser amounts of pollutants. Biomass is also a cleaner option. Wind energy, solar energy and hydro energy are renewable and non-polluting. Hydro energy has been in use since a long time to produce electricity. Wind energy and solar energy have recently come into use. Use of cleaner fuel on a larger scale would help us in saving the environment.
→ Coal: Coal is a black or brownish black sedimentary rock. Coal is used for cooking and in factories. Now-a-days coal is mainly used in thermal power plants.
→ Occurrence of Coal: Coal is found deep inside the earth. Jharkhand, Chhattisgarh, Odisha and West Bengal are the states where major coal mines of India are located. Jharia, Bokaro and Raniganj have the largest coal mines.
→ Formation of Coal: Millions of years ago, plants got buried in swamps. Over a period of time, intense pressure and heat inside the earth changed them into coal.
→ Types of coal: Peat, lignite, bituminous and anthracite are different types of coal. They differ from each other in the content of volatile material and percentage of carbon, moisture and other elements.
→ Processing of coal: Coal is processed through destructive distillation. This is done by strong heating of coal in the absence of air. This helps in retaining useful contents of coal and removing unwanted components so that coal can produce optimum amount of energy. Coke, coal tar, and coal gas are also obtained during destructive distillation of coal.
→ Uses of Coke:
- It is used as domestic as well as an industrial fuel. It gives little or no smoke.
- It is used for extraction of metals.
- It can be used to make fuel gases like water gas (CO + H2).
→ Uses of Coal Tar:
- It is used in manufacturing of synthetic dyes, drugs, explosives, perfumes, plaster, paints, photographic materials, roofing materials.
→ Uses of Coal gas:
- It is used as a domestic fuel.
- It is used as industrial fuel in those industries which are located near coal processing units.
→ Energy : The capacity to do work ¡s called energy.
→ Fuel : A substance which gives heat and light on burning in air is called fuel.
→ Fossil fuel : Fuels which were formed from remains of plants and animals; over millions of years.
→ Air pollution : Addition of impurities in air which makes it harmful for living beings.
→ LPG : Liquefied Petroleum Gas
→ CNG : Compressed Natural Gas
→ Bio Gas : Gas produced on decomposition of biomass.
→ Petroleum products and their uses:
| Petroleum product | Characteristics | Uses |
| Asphalt | Black, sticky liquid | Making upper surface of road, coating the underside of electric poles |
| Paraffin wax | White semi solid | Used as grease, for making Vaseline, ointments and candles |
| Lubricating oil | Thick viscous liquid | Lubricating machine parts |
| Fuel oil | Viscous fluid | As fuel in boilers |
| Diesel oil | Thick viscous fluid | As fuel in generators, heavy vehicles, trains, etc. |
| Kerosene | Liquid | As domestic fuel |
| Gasoline or petrol | Liquid | As fuel in cars, scooters, etc. for dry cleaning |
| Petroleum gas | Gas | Liquefied to make LPG (Liquefied Petroleum Gas) to be used as domestic fuel |