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# Conventional sources of energy

Tutormate > CBSE Syllabus-Class 10th Physics > Conventional sources of energy

## 05 Sources of energy

#### FOSSIL FUELS

• Fossil fuels are natural energy sources formed by processes such as decomposition of buried organic matter.
• When organic matter is buried, the decomposing matter is exposed to heat and pressure over time in the earth’s crust for millions of years.
• Fossil fuels amount for almost 80% of the energy produced on Earth.
• This is mainly because fossil fuels are used extensively from heating stoves in villages to huge power plants that generate enough electricity for millions of people.
• The materials which are burnt to produce heat energy are known as fuels. Examples of fuels are: Wood, Coal, Cooking gas (L.P.G), Kerosene, Diesel and petrol.
• Calorific Value: The amount of heat produced by burning 1 gram of a fuel completely is called its calorific value.
• The common unit of measuring calorific value is kilojoules per gram (kJ/g). Hydrogen gas has the highest calorific value of 150 kilojoules per gram.
• Ignition Temperature: The minimum temperature, to which a fuel must be heated so that it may catch fire and start burning, is known as its ignition temperature.
• The world’s power demands are constantly increasing. It is further expected to increase by 60% by 2030.
• Fossil fuel share in energy production is also expected to rise with 85% of energy generated by fossil fuel by 2030.
• Out of the three conventional sources of energy, coal is the most inefficient and polluting. And there are 50,000 active coal plants worldwide.
• Due to this coal reserves are expected to be used unreservedly. But the combined carbon emission of thermal power plants in the world is enormous, almost twice the amount that can be removed from the atmosphere through natural processes. So, the problems of pollution and global warming are expected to worsen.

#### CHARACTERISTICS OF AN IDEAL FUEL (OR GOOD FUEL)

• It should have a high calorific value.
• It should burn without giving out any smoke or harmful gases.
• It should have a proper ignition temperature,
• It should be cheap and easily available.
• It should be easy to handle, safe to transport, and convenient to store.
• It should not leave much ash behind after burning.
• It should burn smoothly.

#### THERMAL POWER PLANT

• It is a power plant, in which the heat required to make steam for driving turbine (to make electricity) is obtained by burning fuels (coal, petroleum or oil or gas).
• The chemical energy of fuel /Coal is burnt to produce heat energy.
• The thermal energy released by burning of fuel is concerted to mechanical energy by a turbine.
• This mechanical energy is then converted into electrical energy using a generator.
• The typical efficiency for large scale thermal power plant is around 20-25% for the plant using coal and oil and 40% for gas powered turbines.
• As transporting coal/petroleum is much more efficient than transmission of electricity, thermal power plants are set up near coal or oil fields.
• The thermal energy of fuel is also used to heat water.
• The heated water is converted into steam which is pressurized. The pressurized steam is let out into the row of blades of the turbine.
• Due to impulse of the hot pressurized gas the blades rotate.
• The rotation is transferred through a shaft which is coupled to the shaft of the generator.
• Thus, mechanical energy is converted into electrical energy.
• Turbines may be Steam or Gas turbines depending on the medium used to obtain mechanical energy.

#### TURBINE

• A turbine is an elongated column.
• It consists of many rows of small blades.
• The fixed row is called ‘stators’ and the movable row is called ‘rotors’.
• Such rows are arranged alternatively.
• It is then mounted on a rotating horizontal axis, one end of which drives the electrical generator for generation of electricity.

#### HYDRO-POWER PLANT (OR HYDROELECTRIC POWER PLANT)

##### HYDROELECTRICITY:

• Hydroelectricity is the conversion of the kinetic energy of water flowing through rivers or stored in a dam into electricity.
• Hydro-power plant: At a hydroelectric power house, the potential energy of water is first converted into kinetic energy which is then converted into electrical energy.
• It is a power plant that produces electricity by using flowing water to rotate a turbine (which drives the generator)

A hydro-power plant converts the potential energy of water stored in the reservoir of the tall dam into electric energy.

##### PRODUCTION OF HYDROELECTRICITY:

• In order to produce electricity, high-rise dams are constructed on the river to obstruct the flow of water and thereby collect water in larger reservoirs.
• Kinetic energy gets converted into potential energy as the water level rises.
• The sluice gates (sliding gates) at half the height of dam are opened to allow some of the stored water to escape.
• This water is taken through pipe to the turbine installed at the bottom of the dam.
• A high pressure jet of fast flowing water pushes on the blades of turbine with a great force and makes the turbine rotate rapidly.
• The turbine is connected to generator. The generator produces electricity.

• The generation of electricity from flowing water does not produce any environment pollution:
• Flowing water is a renewable source of electric energy which will never get exhausted.
• The construction of dams on rivers helps in controlling floods, and in irrigation.

• Large eco-systems are destroyed.
• The dams can be constructed only in a limited number of places, preferably in hilly terrains.
• Large areas of agricultural land and human inhabitation are to be sacrificed as they get submerged.
• The vegetation which is submerged rots under anaerobic conditions and gives rise to large amounts of methane which is also a green-house gas.