Home CBSE CBSE Class X: Science Chapter 14 : Sources of Energy Notes

CBSE Class X: Science Chapter 14 : Sources of Energy Notes


Chapter 14

Sources of Energy

The source of energy is that which is capable of providing enough useful energy at a steady rate over a long period of time.

A good source of energy should be:

  • Safe and convenient to use, For example; Nuclear energy can be used only by highly trained engineers with the help of nuclear power plants. It cannot be used for our household purpose.
  • Easy to transport, For example; coal, petrol, diesel, LPG etc. can be transported from the places of their production to the consumers.
  • Easy to store, For example; huge Petrol, diesel, LPG can be stored using tanks. etc.


Characteristics of a good fuel:-

  • It has a high calorific value.
  • It produces less smoke.
  • It also Produces fewer residues after burning.
  • Easy availability and Inexpensive.
  • It’s easy to store and transport.


Classification of Sources of energy

Basically, the sources of energy can be classified as follows:

  1. Renewable sources of energy.
  2. Non-Renewable sources of energy.
  1. Renewable sources of energy: Renewable sources of energy are those which are inexhaustible, i.e., which can be replaced as we use them and can be used to produce energy again and again. These are available in an unlimited amount in nature and develop within a relatively short period of time.


  • Solar energy.
  • Wind energy.
  • Water energy (hydro-energy).
  • Geothermal energy.
  • Ocean energy.
  • Biomass energy (firewood, animal dung and biodegradable waste from cities and crop residues constitute biomass).

Advantages of Renewable Sources of Energy

  • These sources will last as long as the Earth receives light from the sun.
  • These sources are freely available in nature.
  • These sources do not cause any pollution.


  1. Non-Renewable Source of Energy: Non-renewable sources of energy are those which are exhaustible and cannot be replaced once they have been used. These sources have been accumulated in nature over a very long period for millions of years.

Disadvantages of Non-renewable Sources of Energy

  • Due to their extensive use, these sources are fast depleting.
  • It is difficult to discover and exploit new deposits of these sources.
  • These sources are a major cause of environmental pollution.


Fossil Fuels: Fossil fuels are the remains of prehistoric plants and animals which got buried deep inside the earth millions of years ago due to some natural processes.

These fossil fuels are non-renewable sources of energy and cause environmental problems due to pollution.

Formation of Fossil Fuels: During its formation, an entire organism or its parts often get buried in sand or mud. These, then decay and disintegrate leaving no signs of their existence. After their death settles down and are covered by sediments and subjected to extreme pressure and temperature or the Earth converts them into fossil fuels, the process is referred to as fossilization.

The disadvantage of Fossil Fuels

  • The fossils are non-renewable sources of energy and once used cannot be renewed.
  • The burning of fossil fuels causes air pollution.
  • The fossil fuels reserves on Earth are limited and may get exhausted soon.


Thermal Power Plants: It generates electricity from heat produced by the combustion of coal.

  • Using coal, petroleum and natural gas to produce thermal electricity.
  • Electricity transmission is very efficient.
  • The steam is produced by burning fossil fuels and the turbine to produce electricity.

Working of thermal power plants:-

Fig: Working of Thermal power plant

  • Initially, Fossil Fuels such as coal are burnt
  • They are used to heat water to produce steam
  • The steam from these moves turbines
  • The movement of these turbines generates electricity
  • This is called a Thermal Power Plant because the heat energy obtained from burning fossil fuels is used to generate electricity.
  • Thermal power plants are generally found near coal and oil fields.

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

Source of energy are also classified as

  • Conventional sources of energy
  • Non- conventional sources of energy

(i) Conventional Sources of Energy are those which are used extensively and meet a marked portion of our energy requirement and these are :

(a) Fossil fuels (coal, oil and natural gas) and

(b) Hydro energy (energy of water flowing in rivers).

Biomass energy and wind energy also fall in this category as these are being used since ancient times.

(ii) Non-conventional Sources of Energy are those which are not used as extensively as the conventional ones and meet our energy requirement only on a limited scale. Solar energy, ocean energy, (tidal energy, wave energy, ocean thermal energy, OTE), Geothermal energy and nuclear energy belong to this category. These sources of energy which have been tapped with the aid of advances in technology to meet our growing energy needs are also called alternative sources of energy.


  1. Solar Energy: The energy produced by the sun in the form of heat and light energy is called solar energy. Solar radiations can be converted into electricity through solar cells (Photovoltaic cells). Photovoltaic cells convert solar radiations directly into electricity through silicon solar cells. Solar cells arranged on large flat sheets form a Mirror solar panel.
    Solar cookers are painted black from the outside and a large glass plate to trap solar radiation by the greenhouse effect. A device that utilizes solar energy for cooking purposes is called a solar cooker. The most commonly used form of solar cooker is known as a box-type solar cooker. A box-type solar cooker is shown in the figure.

Fig: Solar Cookers


Construction of a box-type solar cooker: A box-type solar cooker consists of the following components:

Box (B): This is an insulated metal or a wooden box. It is painted black from the inside because the black surface absorbs more heat. The box may be provided with four roll-wheels.

Glass cover (G): A cover made of two sheets of toughened glass held together in an aluminium frame is used as a cover of box B.

Plane mirror reflector: A plane mirror reflector fixed in a frame is fixed to box B with the help of hinges. The mirror reflector can be positioned at any desired angle to the box. The mirror is positioned so as to allow the reflected sunlight to fall on the glass cover of the box.

Cooking containers: A set of containers made of aluminium and blackened from outside are kept in box B. These containers are also painted black because the black surface absorbs more heat.


Working: The food is cooked in a shallow vessel of the container. The box has a transparent covering of a glass sheet over it. The solar cooker is placed in sunlight and the reflector (plane mirror) is adjusted in such a way that a strong beam of sunlight enters the box through the glass sheet. The blackened metal surfaces in the wooden box absorb infra-red radiations from the beam of sunlight and the heat produced raises the temperature of a blackened metal surface to about 100°C.

The food absorbs heat from the black surface and gets cooked. The thick glass sheet does not allow the heat produced to escape and thus, helps in raising the temperature in the box to a sufficiently high degree to cook the food.

Advantages of Solar Cookers

  • Eco-friendly.
  • Used in rural areas.
  • Retains all the nutrients in food due to slow cooking.

The disadvantage of Solar Cookers:

  • Silicon cells are expensive.
  • Solar radiations are not uniform over the Earth’s surface.
  • Cannot be used at night or on cloudy days.
  • Cannot be used to make chapattis for frying as these require a temperature of 140°C or more. (Maximum temperature of 100°C only can be achieved in a solar cooker) Other Solar Devices are solar water heaters and Solar furnaces.


  1. Wind Energy: When large masses of air move from one place to another then it is referred to as wind. During this process, kinetic energy gets associated with it which is referred to as wind energy. It can be converted into mechanical and electrical energy. The kinetic energy of wind is used in running windmills, which are used to lift water, grind grains etc.

Fig: Wind energy

Uses of Wind Energy

The important uses of wind energy are:

  • It is used to drive windmills, water lifting pumps, flour mills, etc.
  • It is used to propel sailboats.
  • It is used to fly engine fewer aeroplanes or gliders in the air.
  • It is used to generate electrically used for various purposes like lightning, heating, etc.


  • Eco-friendly


  • Wind speed does not uniform always.
  • Needs a large area to erect a series of windmills.
  • A big amount of investment is needed.
  • The output is less as compared to investment.


  1. Hydro Power Plant (hydro energy): When the water flowing in a river is stored in a high rise dam and allowed to fall from the top of the dam. The water rushes down with a great force, which can be utilized to drive a large water Turbine. These turbines are connected with electric generators which generate electric current. The electricity generated in this process is termed hydroelectricity or hydropower. In fact, the process involves the transference of the potential energy of the water into kinetic energy and then into electric energy.

Fig: Hydro Energy

It is the most conventional renewable energy source obtained from water falling from a great height. It is the clean and nonpolluting source of energy. Dams are constructed to collect water flowing in high altitude rivers. The stored water has a lot of potential energy. The water is allowed to fall from a height, the potential energy changes into kinetic energy. Then the turbines are induced to produce electricity.

Advantages of Hydro Power Plant:

  • It is readily and abundantly available everywhere free of cost.
  • It is eco-friendly and does not produce any kind of environmental pollution.
  • It is a renewable source as water itself is a renewable and inexhaustible resource.
  • It is a cheap source of energy, as it does not involve any costly investment.

Disadvantages of Hydro Power Plant:

  • Highly expensive to construct.
  • Dams cannot be constructed on all river sites.
  • Large areas of human habitation and agriculture fields get submerged.
  • People face social and environmental problems.


  1. Geothermal Energy: Geothermal energy is the heat of the Earth and is the naturally occurring thermal energy found within rock formations and the fluids held within those formations. Energy harnessed from the heat of the Sun is called Geo-Thermal Energy. Magma is formed when this heat melts the rocks. The rocks and hot gases are called magma. The magma gets collected at some depths below the Earth’s surface. These places are called ‘Hot spots’. When underground water comes in contact with these hot spots, it changes into steam, which can be used to generate electricity.

(1) The extremely hot rocks present below the surface of the earth heat the underground water and turn it into steam.

(2) As more and more steam is formed between the rocks, it gets compressed to high pressures.

(3) A hole is drilled into the earth up to the hot rocks and a pipe is put into it. The steam present around the hot rocks comes up through the pipe at high pressure.

(4) This high-pressure steam turns the turbine of a generator to produce electricity

5) Sometimes two holes are drilled into the earth in the region of hot rocks and two pipes are put into them.

6) Coldwater is pumped in through one of the pipes. This cold water is turned into steam by the hot rocks. The steam thus formed comes out through the other pipe and is used to generate electricity.

Advantages of Geo-Thermal Energy

  • Renewable
  • Inexpensive

Disadvantages of Geo-Thermal Energy

  • Only a few sites are available for harnessing energy.
  • Expensive


  1. Ocean Energy: The oceans acquire almost 71% of the surface of the Earth. The enormous amount of water present in them did not act as a big collector of solar heat energy but also store a large amount of it due to its high specific heat. Thus, ocean water can be used as a renewable resource of energy.

The main forms of ocean energy are described as under:

(i) Ocean Thermal Energy: The energy available due to the temperature difference between the deeper levels and surface of an ocean is called Ocean Thermal Energy,

(ii) Ocean Tidal Energy: The rise of ocean water due to the attraction of the moon is referred to as high tide and its fall as low tide. The enormous movement of water due to high and low tide provide a large amount of energy known as Ocean Tidal Energy. This tidal energy can be utilized by constructing a tidal barrage or dam.

(iii) Sea Wave Energy: The energy obtained from high-speed sea waves is referred to as sea wave energy. Infect, these high-speed sea waves have a lot of kinetic energy associated with them, which can be used to drive dynamos that convert kinetic energy into electrical energy.

(iv) Energy from Nuclear Deuterium of Oceans: The oceans water contains an unlimited amount of heavy hydrogen isotope called as deuterium which is isotope hydrogen having one neutron in its nucleus. Scientists are working hard to produce energy by carrying the controlled nuclear fission of deuterium isotope. The process is still in its experimental stage.

(v) Energy From Salinity Gradient in Seas: The difference in the concentration of salts in the water of the two or more seas is called a salinity gradient. This salinity gradient is now a day used to obtain energy with the involvement of suitable techniques

(vi) Energy From Sea Vegetation or Biomass: Sea vegetation or biomass is another direct source of energy because the enormous amount of seaweeds present in the seawater provides an endless supply of methane fuel.


  1. Bio-Mass: Biomass is defined as living matter or its residue and is a renewable source of energy. The biomass includes
  • All the new plant growth
  • Agriculture and forest residues (like Bio-gases, dark, sea dust, wood shavings, roots, animals dropping, etc..),
  • Carbonaceous wastes (like sewage, garbage, night-soil, etc.)
  • Biodegradable organic effluent from industries.
  • It is the source of the conventionally used fuels that are used in our country. For example; Cow dung cakes, firewood, coal, charcoal etc.

Fig: Bio-mass energy

Plant and animal wastes (dung), vegetable wastes, sewage are decomposed in absence of oxygen to produce Biogas Since the source of these fuels is animal dung, the source of these fuels is called Biomass. It is commonly called Gobar-gas

Bio-gas: It is a mixture of gases produced during the decomposition of biomass in the absence of oxygen. (Anaerobic Respiration). Methane is the major component of bio-gas.

Biogas plants: Animal dung, sewage, crop residues, vegetable wastes, poultry dropping, etc. are used to produce Bio-gas in Bio-gas plants.

Advantage of Bio-gas:

  • A Bio-gas plant, is quite simple, can easily be built in rural areas. A small plant using dung from 3 to 4 heads of cattle is capable of supplying Bio-gas for 6 hours daily for cooking purposes.
  • Biogas is a clean fuel that burns without smoke and leaves no ash.
  • The main constituent of Bio-gas, i.e., ethane has a higher calorific value (55 kj/g) than of petrol (50kj/g).
  • The spent slurry, being rich in nitrogen and phosphorus is good manure.
  • By using Bio-gas, firewood is saved and deforestation is reduced.

Composition of Biogas: Biogas is mainly composed of methane (up to 75%), C02 (25%) and traces of other gases such as nitrogen and hydrogen. Whereas methane is a high-value calorific fuel, carbon dioxide is an inert gas.


  1. Nuclear Energy: A reaction in which, the nucleus of an atom undergoes a change to form a new atom and releases an enormous amount of energy is called nuclear energy. There are two distinct ways of obtaining nuclear energy,

The energy released when some changes take place in the nucleus of the atom of a substance is called Nuclear energy. It is used for heat generation, fuel for marine vessels.

(a) Nuclear fission: In a process called nuclear fission the nucleus of a heavy atom (such as uranium, plutonium or thorium) when bombardier with low-energy neutrons, can be split apart into lighter nuclei. When this is done, a tremendous amount of energy is released if the mass of the original nucleus is just a little more than the sum of the masses of the individual products. The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal. In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be part of a self-sustaining fission chain reaction that related energy at a controlled rate. The energy released energy can be used to produce steam and further generate electricity.

(b) Nuclear fusion: Currently all commercial nuclear reactors are based on nuclear fission. But there is another possibility of nuclear energy generation by a safer process called nuclear fusion. Fusion means joining lighter nuclei to make a heavier nucleus, most commonly hydrogen or hydrogen isotopes to create helium, such as,

2H+2H        3He (+n)

It releases a tremendous amount of energy, according to the Einstein equation, as the mass of the product is a little less than the sum of the masses of the original individual nuclei. Such nuclear fusion reactions are the sources of energy in the sun and other stars. It takes considerable energy to force the nuclei to fuse. The conditions needed for this process are extreme-millions of degrees of temperature and millions of Pascal’s of pressure. The hydrogen bomb is based on the thermonuclear fusion reaction. A nuclear bomb based on the fission of uranium or plutonium is placed at the core of the hydrogen bomb. This nuclear bomb is embedded in a substance that contains deuterium and lithium. When the nuclear bomb (based on fission) is detonated, the temperature of this substance is raised to 107 K in a few microseconds. the high temperature generates sufficient energy for the light nuclei to fuse and a devastating amount of energy is released.

Advantages of Nuclear Energy

  • The alternative source of energy due to depletion of fossil fuels.
  • From a small amount of fuel, a large amount of energy is released.

Disadvantages of Nuclear Energy :

  • Risk of nuclear waste leakage.
  • High cost of setting up of the nuclear plant.
  • Pollution of environment.

Environmental consequences:

  • The combustion of fossil fuels produces acid rain and damages plants (crops), soil and aquatic life.
  • The burning of fossil fuels is increasing the amount of greenhouse gas, carbon dioxide in the atmosphere.
  • The construction of hydropower plants is a disturbing ecological balance.
  • Nuclear power plants are increasing radioactivity in the environment.

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