Energy Science class-10




The working capacity of an object is called energy. Its SI unit is joule and CGS unit is calorie.


Primary source of energy:

The sources of energy that can be used in the same form, as they are available in nature are called primary sources of energy, they are of two types:

i) Non renewable source of energy.

ii) Renewable source of energy.


Non Renewable Source of energy:

The sources of energy which cannot be reused or which gets depleted, it takes longer time for the formation is called non renewable source of energy. For example, fossil fuel energy like coal, petroleum and natural gas.


Renewable source of energy:

The source of energy which can be reformed in a short period of time once they are used up is called renewable source of energy. For example, Solar energy, Biomass, Wind energy, etc.


Solar energy:

The heat and light energy given by the sun is called solar energy. It is produced by nuclear fusion. The sun radiates about 27 x 1023 kW of energy per second. The earth receives 1.4 kW of energy per square meter in average.


Sun: Major source of energy:

Solar energy is stored in all the sources of energy like fossil fuel energy, hydroelectricity, biofuel energy, Tidal energy, Geothemal energy, Wind energy, etc. Therefore, the sun is called major source of energy.


Conditions required for nuclear fusion reaction in the sun:

i) There is sufficient hydrogen gas in the sun.

ii) There is an abundance of helium gas in the sun, which is formed by the fusion of hydrogen atoms.

iii) Extremely high temperature is in the sun, which causes hydrogen atoms to split their nuclei.

iv) Extremely high pressure is in the sun, which causes the similar charged nuclei to fuse together.


Fossil fuel:

The dead remains of plants and animals that were buried inside the earth’s crust millions years of ago, such preserved dead bodies are called fossils. The fuel formed from a huge mass of such fossils is called fossil fuel. It includes coal, mineral oil and natural gas.



Coal is the solid and carbon-enriched form of fossil fuel. It is formed from the dead remains of plants that were buried deep inside the earth’s crust million years of ago. Anthracite is the best quality coal.


Types of Coal:

i) Anthracite: It contains 90% carbon.

ii) Lignite: It contains 70% carbon.

iii) Bituminous: It contains 80% carbon.

iv) Peat: It contains 60% carbon.


Mineral oil:

Mineral oil is the liquid form of fossil fuel. The liquid torm of fossil fuel, such as petrol, diesel, kerosene. mobile, etc. is called mineral oil. Mineral oil is the petroleum substance, which is formed from the dead remains of plants and animals that were buried deep inside the earth’s crust million years of ago. It is obtained as crude oil. When the crude oil is refined, various products of petroleum are obtained. It includes petrol, diesel, kerosene, mobil, wax, etc.


Advantages ol Fossil fuel (coal and mineral oil):

i) It is cheaper and more abundant in comparison to other types of fuels.

ii) It can be easily transported from one place to another.

iii) It is multipurpose fuel.

iv) It is used to nin ditferent vehicles, engines, in industries and factories that require abundant heat supply.

v) It is used in generation of electricity.



The electricity generated by rotating turbines with the help of water energy is called hydro-electricity. About 83,000 MW hydroelectric potential is in Nepal.


Advantages and utilities of Hydro-electricity:

i) It is cheaper in a long term basis though the initial cost of production is high.

ii) It does not produce any kind of pollution like dust, smoke, radiation, etc.

ii) It is a renewable source of energy. So, it is never depleted.

iv) It is cheaper and easy for transmission.

v) It is multipurpose source of energy.

vi) It operates the modern devices like computer, TV and other electrical appliances.


Alternative Sources of energy:

The renewable sources of energy, which are used as the alternative of non-renewable energy, are called alternative sources of energy. Such sources of energy are used to replace the conventional sources of energy. For example, Bio-fuel, Wind energy, Nuclear energy, Tidal energy,etc.


Important alternative sources of energy in the context of Nepal:

i) Hydro-electricity

ii) Wind energy

iii) Solar energy

iv) Bio-fuel



Bio-fuel refers to the energy source, which is obtained, from the plants and animals. It includes wood, bio-mass, biogas, sawdust, chaff and fragments of straw.


Bio-mass and Bio-mass Energy:

The pieces made from the compression of saw dust, chaff, wood, chaff and fragments of straw by machine is called bio-mass. The energy obtained from biomass is called biomass energy.



The decay of garbage, cattle dung, sewage and other residue in the absence of air produces a gas, which is called bio-gas. Biogas is the mixture of methane, carbon dioxide and hydrogen gas.


Advantage of Bio-gas:

i) It is a renewable source of energy. So it is never exhausted.

ii) It produces more heat w hile burning.

iii) It is cheaper and can be produced easily in domestic level.

iv) It does not cause air pollution.

v) It can be used to get heat, light and to generate electricity.


Nuclear energy:

The energy generated either by nuclear fusion or nuclear fission is called nuclear energy. Those substances which are used to produce nuclear energy in nuclear power plant are called nuclear fuel. For example Uranium, Plutonium, etc.


Nuclear reaction:

The reactions in which the nucleus of an atom undergoes a change forming new atoms by fusion or ission and releasing a tremendous amount of energy are called nuclear reactions. They are of two types:

i) Nuelear fission reaction.

ii) Nuclear fusion reaction


Nuclear Fission Reaction:

When a heavy nucleus of any radioactive element splits up into two or more than two lighter nuclei with liberation of tremendous amount of energy, then it is called nuclear fission reaction.

For example, Uranium nucleus (92U235) splits up into Barium and Krypton nuclei with the release of energy.

92U235 + 0n1 —-> 56Ba141 + 36Kr92 + 3 0n1 + Q (Energy)


Nuclear Fusion Reaction:

When two or more than two lighter nuclei fuse together to form a slightly heavier nucleus, tha it is called nuclear fusion reaction.

For example:

21H1 + 21H1 — enormously high temperature and pressure —> 2He4 + 21e0 + energy


E = mc2 Equation:

The energy released during nuclear reaction can be calculated by using the Einstein equation E= mc2. This is called theory of relativity.

Where E = energy released, m = loss of mass and c = velocity of light in vacuum.


Tidal energy:

The energy, which can be obtained from Ihe tides of sea, is called tidal energy. Such type of energy source is impossible in Nepal because there is no Sea.


Wind energy:

The energy obtained from blowing wind is called wind energy. Wind energy is used to rotate turbines to generate electricity. Nowadays, wind mills are operated by wind energy to generate electrical energy.


Geo-thermal energy:

The energy, which can be obtained from the heat present inside the earth, is called geothermal energy.


Energy crises:

The state of shortage of energy sources on the earth due to over population, urbanization and industrialization that we are going to face in near future is called energy crises. At the state of energy crises, there is maximum demand of energy but less supply.


Main causes of energy crises:

i) High demand of energy sources because of population growth, industrialization and urbanization.

ii) Over use of non-renewable source of energy.

iii) Lack of development and the use of alternative and renewable sources of energy.

iv) Due to lack of conservation of present source of energy.


Ways to solve energy crises:

i) By using existing sources of energy wisely and economically.

ii) By conserving existing sources of energy.

iii) By developing alternative sources of energy.

iv) By controlling population growth.





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