Work, Energy and Power
Category : 9th Class
Work, Energy and Power
Work
If a body gets displaced when a force acts on it, work is said to be done. Work is measured by the product of force and displacement of the body along the direction of force,
If a body gets displaced by S when a force F acts on it, then the work \[\operatorname{W}= F\,S cos\theta \]
Where \[\theta \] = angle between force and displacement.
If both force and displacement are in the same direction/ then W = FS.
Work is a scalar quantity and its SI unit is joule.
Energy
Capacity of doing work by a body is called its energy.
Mechanical energy is two types.
(i) Potential Energy |
(ii) Kinetic Energy |
Potential Energy: The capacity of doing work developed in a body due to its position or configuration is called its potential energy.
Example:
(i) energy of stretched or compressed spring |
(ii) energy of water collected at a height |
(iii) energy of spring in a watch. |
Kinetic Energy: Energy possess by a body due to its motion is called kinetic Energy of the body:
Principle of Conservation of Energy
Some Equipments used to Transform Energy
S. No. |
Equipment |
Energy Transformed |
1. |
Dynamo |
Mechanical energy into electrical energy |
2. |
Candle |
Chemical energy into light and heat energy |
3. |
Microphone |
Sound energy into electrical energy |
4. |
Loud Speaker |
Electrical energy into sound energy |
5. |
Solar Cell |
Solar energy into electrical energy |
6. |
Tube light |
Electrical energy into light energy |
7. |
Electric Bulb |
Electrical energy into light and heat energy |
8. |
Battery |
Chemical energy into electrical energy |
9. |
Electric motor |
Electrical energy into mechanical energy |
10. |
Sitar |
Mechanical energy into sound energy |
Power
Rate of doing work is called power. \[P=\frac{W}{t}\]
Watt = joule/sec.
1 kW = 1000 watt \[={{10}^{3}}\] watt
1 MW = 1000000 watt \[={{10}^{6}}\] watt
1 Watt second\[= 1 watt\,\times \,\,1 second=1 joule\].
1 Watt hour (Wh) = 3600 joule
1 kilowatt hour (kWh) \[=\text{ }3.6\times {{10}^{6}}\] joule.
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