CBSE Class 10 Science Sources of energy Notes

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SOURCES OF ENERGY

ENERGY: - Whenever a body is capable of doing work, the body is said to possess energy. Thus energy is defined as the ability of a body to do work and the amount of energy possessed by a body is equal to the amount of work it can do when its energy is released.

Energy comes in different forms and one form can be converted to another. For example, if we drop a plate from a height, the potential energy of the plate is converted mostly to sound energy when it hits the ground.

Units of energy: - On S.I. system, energy is measured in the units of joules or in calories, and on C.G.S. system in ergs. However, the commercial unit of energy is kilowatt-hour. The energy is said to be one kilowatt-hour, when a body consumes one kilowatt of energy in one hour.

Sources of energy :- a 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 :

i) Safe and convenient to use, e.g., nuclear energy can be used only by highly trained engineers with the help of nuclear power plants. It cannot be used for our household purposed.

ii) Easy to transport, e.g., coal, petrol, diesel, LPG etc. Have to be transported from the places of their production to the consumers.

iii) Easy to store, e.g., huge storage tanks are required to store petrol, diesel, LPG etc.

Characteristics of an ideal or a good fuel:

1. It should have a high calorific or a heat value, so that it can produce maximum energy by low fuel consumption.

2. It should have a proper ignition temperature, so that it can burn easily.

3. It should not produce harmful gases during combustion.

4. It should be cheap in cost and easily available in plenty for everyone.

5. It should be easily and convenient to handle, store and transport from one place to another.

6. It should not be valuable to any other purpose than as a fuel.

7. It should burn smoothly and should not leave much residue after its combustion.

INTEXT QUESTIONS 

1. What is a good source of energy?

Ans. A good source of energy fulfils the following criteria:

1. It produces a lot of heat per unit mass.

2. It does a huge amount of work per unit mass.

3. It is easily accessible.

4. It is easy to store and transport.

5. It is economical.

6. It produces less amount of smoke.

Ans. A good fuel produces a huge amount of heat on burning, does not produce a lot of smoke, and is easily available.

3. If you could use any source of energy for heating your food, which one would you use and why?

Ans. Natural gas can be used for heating and cooking food because it is a clean source of energy. It does not produce huge amount of smoke on burning. Although it is highly inflammable, it is easy to use, transport, and it produces a huge amount of heat on burning.

CLASSIFICATION OF SOURCES ENERGY :

The sources of energy can be classified as follows :

(i) Renewable
(ii) Non-Renewable.

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.

Examples of Renewable Sources of Energy.
(i) Solar energy, (ii) Wind Energy, (iii) water energy (hydro-energy), (iv) geothermal energy,
(v) ocean energy, (vi) biomass energy (firewood, animal dung and biodegradable waste from cities and crop residues constitute biomass).

Advantages of Renewable Sources of Energy :
(i) These sources will last as long as the Earth receives light from the sun.
(ii) These sources are freely available in nature.
(iii) These sources do not cause any pollution.

2. Non-Renewable Sources 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 of million of years.

Examples of Non-renewable sources of Energy :
(i) Coal (ii) Oil and (iii) Natural gas.
All these fuels are called fossil fuels.

Disadvantages of Non-renewable sources of Energy :
(i) Due to their extensive use, these sources are fast depleting.
(ii) It is difficult to discover and exploit new deposits of these sources.
(iii) These sources are a major cause of environmental pollution.

CONVENTIONAL AND NON-CONVENTIONAL SOURCES OF ENERGY :
Sources of energy are also classified as :
(i) Conventional sources of energy
(ii) Nonconventional sources of energy.

CONVENTIONAL SOURCES OF ENERGY

FOSSIL FUELS
Fossil fuels are the remains of prehistoric plans and animals which got buried deep inside the early millions of years ago due to some natural processes.
The energy of fossil fuels is in fact, that solar energy which was trapped by natural processes a very long time ago. Coal, petroleum and natural gas are fossil fuels.
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. Infact, the harder parts of organisms after their death, settle down and are covered by sediments and subjected to extreme pressure and temperature of the earth converts them into fossil fuels, the process being referred to as fossilization. Disadvantages of Fossil Fuels:

1. The fossil fuels are non-renewable sources of energy and once used cannot be renewed.
2. Burning of fossil fuels causes air pollution.
3. The fossil fuels reserves in the earth are limited and may get exhausted soon.

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

HYDRO POWER PLANTS
Hydro power plants convert the potential energy of falling water into electricity. Since there are very few water-falls which could be used as a source of potential energy, hydro power plants are associated with dams. 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 (see the above Fig.). Since the water in the reservoir would be refilled each time it rains (hydro power is a renewable source of energy) we would not have to worry about hydroelectricity sources getting used up the way fossil fuels would get finished one day.

Advantages of generating hydro electricity :- The main advantages of using water
energy for the generation of hydro electricity are listed as under :
1. It is readily and abundantly available everywhere free of cost.
2. It is eco-friendly and does not produce any kind of environmental pollution.
3. It is a renewable source as water itself is a renewable and inexhaustible resource.
4. It is a cheap source of energy, as it does not involve any costly investment.

BIO-MASS
Biomass is defined as living matter or its residue and is a renewable sources of energy. The biomass includes (i) all the new plant growth (ii) agricultural and forest residues (like biogases, bark, sae dust, wood shavings, roots, animal droppings etc.) (iii) Carbonaceous wastes (like sewage, garbage, night-soil, etc.) (iv) Biodegradable organic affluent from industries.
Biogas:- Biogas is a mixture of gases produced by anaerobic degradation of biomass in the presence of water but in the absence of oxygen. It is a renewable source of energy on account of its production fromvastly and continuously available organic wastes.

Advantages of Biogas:- i) A biogas plant, being 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 biogas for 6 hours daily for cooking purposes.
ii) Biogas is a clean fuel that burns without smoke and leaves no ash.
iii) The main constituent of biogas, i.e., ethane has a higher calorific value (55kj/g) that of petrol (50kj/g).
iv) The spent slurry, being rich in nitrogen and phosphorus, is good manure.
v) By using biogas, firewood is saved and deforestation is reduced. Composition of Biogas:- Biogas is mainly composed methane (up to 75%), CO2 (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. Biogas is prepared in biogas plants which are of two types: (i) Fixed Dome Type (ii) Floating Gas Holder Type.

Fixed Dome Type Biogas Plant:-
The main parts of fixed of dome type of biogas plants are:
1. Digester. It is well shaped underground tank made of bricks. Its roof is someshaped which acts as a storage tank for biogas.
2. Mixing tank. It is constructed on the ground level where cattle dung and water are mixed.
3. Inlet tank. It is constructed underground below the mixing tank.
4. Overflow tank. It is constructed slightly below the level of mixing tank.
5. Outlet tank. It is constructed below the overflow tank.

Working of Biogas Plant:-
Cattle dung and water are mixed in equal proportion in the mixing tank to form slurry. This slurry is fed into the digester tank through inlet tank when the digester tank is filled about 2/3rd of its capacity, the dome is left free for collection of biogas. The slurry undergoes anaerobic fermentation and biogas is produced after 50 to 60 days. As biogas is collected in the dome it exerts pressure due to which spent slurry go to the overflow tank through outlet tank and fresh slurry is fed into the digester and continuous supply of biogas is obtained spent slurry is used as manure.

WIND ENERGY

Wind Energy: -When large masses of air move from one place to another it is referred to as wind. During this process kinetic energy gets associated with it which is referred to as wind energy.

Principle of utilisation of wind energy: -
Wind energy is efficiently converted into electrical energy with the aid of a windmill. A windmill is a large fan having big blades, which rotate by the force exerted by moving wind on them. These blades remain continuously rotating as long as wind is blowing and can be used to drive a large number of machines like water pumps, flour mills etc. But these days a windmill is used to generate electric current which is used for various purposes and therefore wind power stations are established all over the world which convert wind energy directly into electrical energy.

Uses of wind energy: -
The important uses of wind energy are;
1. It is used to drive windmills, water lifting pumps and flour mills etc.
2. It is used to propel sale boats.
3. It is used to fly engine less aeroplanes or gliders in the air.
4. It is used to generate electricity used for various purposes like lightening, heating etc.

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