Source of Energy Notes Class 10 Science Chapter 14 Cbse Ncert

source of energy class 10 notes
source of energy class 10 notes

    Source of Energy


A good source of energy would be one :-

  •  Which would do a large amount of work per unit volume or mass,

  •  Be easily accessible,

  •  Be easy to store and transport, and

  •  Perhaps most importantly, be economical


1. Fossil Fuels

Fossil Fuels are formed in the geological past from the remains of  dead living organisms. Some examples of fossil fuels are Coal, petroleum and natural gas.

Fossil fuels causes lots of pollution upon burning .

  • The pollution caused by burning fossil fuels can be somewhat reduced by increasing the efficiency of the combustion process and using various techniques to reduce the escape of harmful gases and ashes into the surroundings.

Uses of fossil fuels :-

  1. They are used directly in homes as energy source for cooking food.
  2. Fossil fuels are the major fuels used for generating electricity

2. Thermal Power Plant

Large amount of fossil fuels are burnt every day in power stations to heat up water to produce steam which further runs the turbine to generate electricity.

The term thermal power plant is used since fuel is burnt to produce heat energy which is converted into electrical energy.

The transmission of electricity is more efficient than transporting coal or petroleum over the same distance. Therefore, many thermal power plants are set up near coal or oil fields.

3. Hydro Power Plants

Hydro power plants convert the potential energy of falling water into electricity.

In order to produce hydel electricity, high-rise dams are constructed on the river to obstruct the flow of water and thereby collect water in larger reservoirs. The water level rises and in this process the kinetic energy of flowing water gets transformed into potential energy. The water from the high level in the dam is carried through pipes, to the turbine, at the bottom of the dam.

A schematic view of a hydro power plant
A schematic view of a hydro power plant

Since the water in the reservoir would be refilled each time it rains (hydro power is a renewable source of energy).

Problems with the Constructions of dam:-

Constructions of big dams have certain problems associated with it.

  1. The dams can be constructed only in a limited number of places, preferably in hilly terrains.
  2. Large areas of agricultural land and human habitation are to be sacrificed as they get submerged.
  3. Large eco-systems are destroyed when submerged under the water in dams.
  4. The vegetation which is submerged rots under anaerobic conditions and gives rise to large amounts of methane which is also a green-house gas.
  5. It creates the problem of satisfactory rehabilitation of displaced people.
  6. Opposition to the construction of Tehri Dam on the river Ganga and Sardar Sarovar project on the river Narmada are due to such problems.

    Improvements in the Technology for using Conventional Sources of Energy


Biomass: is fuel that is developed from organic materials. It is a renewable and sustainable source of energy.

Cow dung ,woods are some examples of biomass .

Bio-gas (Gobar Gas)

Bio gas plant has a dome-like structure built with bricks. A slurry of cow-dung and water is made in the mixing tank from where it is fed into the digester. The digester is a sealed chamber in which there is no oxygen. Anaerobic micro-organisms that do not require oxygen decompose or break down complex compounds of the cow-dung slurry. It takes a few days for the decomposition process to be complete and generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide. The bio-gas is stored in the gas tank above the digester from which they are drawn through pipes for use.

Schematic diagram of a bio-gas plant
Schematic diagram of a bio-gas plant


Importance of biogas :-

  • Bio-gas is an excellent fuel as it contains up to 75% methane. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning.
  • Its heating capacity is high. Bio-gas is also used for lighting.
  • The slurry left behind is removed periodically and used as excellent manure, rich in nitrogen and phosphorous.

Wind Energy

Wind energy is also used to generate electricity. A windmill essentially consists of a structure similar to a large electric fan that is erected at some height on a rigid support.

A windmill
A windmill


Electricity generation from wind energy:-

To generate electricity, the rotatory motion of the windmill is used to turn the turbine of the electric generator. The output of a single windmill is quite small and cannot be used for commercial purposes. Therefore, a number of windmills are erected over a large area, which is known as wind energy farm. The energy output of each windmill in a farm is coupled together to get electricity on a commercial scale.

Limitations in harnessing wind energy:-

  1. Wind energy farms can be established only at those places where wind blows for the greater part of a year. The wind speed should also be higher than 15 km/h to maintain the required speed of the turbine.
  2.  There should be some back-up facilities (like storage cells) to take care of the energy needs during a period when there is no wind.
  3. Establishment of wind energy farms requires large area of land. For a 1 MW generator, the farm needs about 2 hectares of land.
  4. The initial cost of establishment of the farm is quite high.
  5. Moreover, since the tower and blades are exposed to the vagaries of nature like rain, Sun, storm and cyclone, they need a high level of maintenance.


Non Conventional Energy sources: Those energy sources which are renewable and ecologically safe.

such as solar energy, wind energy, biomass energy, ocean energy (tidal energy,wave energy, ocean thermal energy),geothermal energy, nuclear energy etc.

1. Solar Energy

A black surface absorbs more heat as compared to a white or a reflecting surface under identical conditions. Solar cookers and solar water heaters use this property in their working. Some solar cookers achieve a higher temperature by using mirrors to focus the rays of the Sun. Solar cookers are covered with a glass plate.

A solar cooker
A solar cooker

These devices are useful only at certain times during the day. This limitation of using solar energy is overcome by using solar cells that convert solar energy into electricity. A typical cell develops a voltage of 0.5–1 V and can produce about 0.7 W of electricity when exposed to the Sun. A large number of solar cells are, combined in an arrangement called solar cell panel (Fig. 14.7) that can deliver enough electricity for practical use.

A solar cell panel
A solar cell panel


Advantages associated with solar cells are:-

  1. They have no moving parts, require little maintenance and work quite satisfactorily without the use of any focussing device.
  2. Another advantage is that they can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable.
  3. Solar cells are used for many scientific and technological applications.
  4. Artificial satellites and space probes like Mars orbiters use solar cells as the main source of energy.
  5. Traffic signals, calculators and many toys are fitted with solar cells.

Drawbacks of solar cells :-

  1. Availability of the special grade silicon for making solar cells is limited.
  2. The entire process of manufacture is still very expensive, silver used for interconnection of the cells in the panel further adds to the cost.

    Energy from the Sea

1. Tidal Energy

The sea-level changes during the day. This phenomenon is called high and low tides. The difference in sea-levels gives us tidal energy.

Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

2. Ocean Thermal Energy

The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold.

This difference in temperature is exploited to obtain energy in ocean-thermal-energy conversion plants.

These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 20 K (20°C) or more.

3. Geothermal Energy

Molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’. When underground water comes in contact with the hot spot, steam is generated.

  • Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs.

The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity. The cost of production would not be much, but there are very few commercially viable sites where such energy can be exploited.

4. Nuclear Energy

Nuclear energy is generated in a process called nuclear fission.

Nuclear fission: 

Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei).  When this is done, a tremendous amount of energy is released.

Drawbacks of nuclear energy :-

  • The storage and disposal of spent or used fuels – the uranium still decaying into harmful subatomic particles (radiations). Improper nuclear-waste storage and disposal result in environmental contamination.
  • Further, there is a risk of accidental leakage of nuclear radiation.
  • The high cost of installation of a nuclear power plant, high risk of environmental contamination and
  • Limited availability of uranium makes large-scale use of nuclear energy prohibitive.


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