Energy is all around us. Energy can neither be created nor destroyed. This is called the law of conservation of energy. It can be changed from one form to another.
Let us consider the following example to understand the meaning of the law of conservation of energy.
The sun is ultimate source of energy. Its energy is absorbed by a tree. It is converted into chemical energy. The tree turns into coal which possesses chemical energy. The chemical energy in coal is converted into heat energy when it is burnt. The heat energy turns water into steams which can rune turbine and railway engine. Here, heat energy is converted into mechanical energy. The turbine is able to run a dynamo which produces electrical energy. This electricity is sent to homes. It lights a bulb, producing light energy. It is sent to a toaster, producing heat energy. It turn s refrigerator, where electrical energy is converted into mechanical energy.
The total quantity of energy in the universe is constant; energy cannot be created, and it cannot be destroyed. The form of energy can be converted into another, or transported from one place to another. But that is as much as can be done. When energy is used, it does not disappear; it is changed into another form.
Sources of Energy:
1. The Sun
The energy from the sun is called solar energy. As stated earlier, this is the ultimate source of energy for the earth. No life on the earth will exist if the sun’s energy stops reaching the earth. Plants use sunlight to make food. Food is source of energy for all living beings. It is observed that each form of energy is ultimately related to solar energy.
2. Fossil fuels
Fuels, such as coal, petrol, diesel, kerosene and natural gas, are called fossil fuels. The remains of ancient plants and animals are called fossils.
Wood is used as a fuel. It has stored chemical energy. On burning, it gives heat and light energy. Coal is formed from green plants that grew millions of years ago. When the plant sided, decayed and got buried under the earth, they changed into coal after millions of years. Coal is used as a fuel.
Petroleum is formed the green plants and the remains of sea plants and animals which got buried millions of years ago. Coal and petroleum have chemical energy stored in them. Petroleum is oil liquid which yields a large number of things, such as petrol, diesel, kerosene, paraffin, and varnish. Therefore, all these products contain chemical energy. Natural gas occurs naturally in the earth, more particularly near deposits of petroleum. It is used as a fuel to provide energy. It contains stored chemical energy.
3. Energy from the Wind
Moving air has energy. It is called wind energy. It can be converted into mechanical energy. It is used to turn windmills. Windmill is a machine made to move by the wind blowing on vanes fixed like spokes of a wheel on a shaft at the top of water. It gives power for grinding grain, pumping water, etc. It can also be used to rotate the generator attached with it to produce electricity.
4. Energy from the Running Water
Running water is a source of energy as it is capable of doing work. It can transport logs of wood from one place to another. Water falling from a height can turn turbines which give electric power. Such power stations where the energy of water is used to generate electricity are called hydel power-stations. (Also called hydroelectric power stations) (‘Hydro’ is the Greek word for ‘water’).
5. Energy from Biomass
Biomass consists of waste material and dead parts of living things. The word ‘biomass’ means bio (dealing with life or living objects) plus mass (material or matter). Thus, biomass means dead parts and waste material of living objects.
Now a days, it has a wider meaning. It includes garbage, excretions of animals, sewage, crop residue, wood and industrial waste materials. There are two ways to use biomass as a source of energy:
To burn the dry biomass and to produce heat energy. It is used for cooking.
To decompose the biomass in the absence of oxygen (air) and to produce methane gas. Methane gas is called biogas.
It is used as a fuel gas for cooking and lighting. The biogas is being produced in villages from cow dung and sewage. The residue is used as manure for plants.
Renewable and Non-renewable Sources of Energy:
The renewable sources of energy are the sources of energy which can be used again and again and are not exhaustible. The examples are sun, water, wind and biomass. Such sources of energy are freely available and are free of cost. They do not pollute the environment.
Sources of energy which are in limited amount and can be exhausted after some time are called non-renewable sources of energy. Once they are used up, they cannot be replaced. Examples are plants, coal, petroleum, petrol, and diesel and natural gas. All fossil fuels are non-renewable sources of energy.
Scientists are exploring new methods to use the renewable sources of energy for the future generations. There are many such sources, which are yet to be explored. These are energy from the tides, cyclones, typhoons and earthquakes.
We should prefer the renewable sources of energy because:
- They are available in plenty
- They are available free of cost
- They do not pollute air
- They are not exhaustible
Hydel power-stations are preferred over thermal power-stations because they do not pollute air; are cheaper and can use the same water again and again. In a thermal power-station, coal once sued cannot be used again; it pollutes air and is not cheap.