[Science] Work, Power & Energy

(Work Power and Energy)

  • 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. W = F S cosθ

  • If both force and displacement are in the same direction then W = F S

  • Work is a Scaler quantity and its SI unit is joule.

  • Power : Rate of doing work is called power.If an agent does W work in time t then power P = W/t

SI unit of power is watt named as a respect to the scientist James watt.

Watt = joule / second

1 Kw = 103 watt

1 MW = 106 watt

Horse power is a practical unit of power.

1 H.P = 746 watt

1 watt second = 1 watt × 1 second = 1 joule

1 watt hour (Wh) = 3600 joule

1 kilowatt hour (Kwh) = 3.6 × 106 joule

W, Kw, MW & HP are units of power.

Ws, Wh, Kwh are units of work and energy.

  • Energy : Capacity of doing work by a body is called its energy. Energy is a scalar quantity and its SI unit is joule.

  • Energy developed in a body due to work done on it is called mechanical energy. Mechanical energy is of two types:

  • (1) Kinetic energy

  • (2) Potential energy

  • Energy possess by a body due to its motion is called Kinetic energy of the body. K.E = m v2

  • The capacity of doing work developed in a body due to its position is called its potential energy. P.E = mgh

Examples : Energy of water collected at a height, Energy in a watch, Energy of stretched or compressed spring.

  • Principle of conservation of energy : Energy can neither be created nor can be destroyed. Only energy can be transformed from one form to another form. Whenever energy is utilized in one form, equal amount of energy is produced in other form. Hence total energy of the universe always remains the same.

  • Examples of transformation of energy:

    Electric bulb : Electrical energy into light and heat energy.

  • Electric cell : Chemical energy into electrical energy.

  • Dynamo : Mechanical energy into electrical energy.

  • Solar cell : Solar energy into electrical energy.

  • Electric motor : Electrical energy into mechanical energy

  • Microphone : Sound energy into electrical energy.

  • Loud speaker : Electrical energy into sound energy.

  • Sitar : Mechanical energy into sound energy.

  • Candle : Chemical energy into light and heat energy.

  • Solar energy : Sun is a great source of energy.The sun contains 70% Hydrogen, 28% Helium and rest 2% are other substances.

  • The temperature and pressure of the center of the sun are 1.5 × 107K and 2 ×1016 Newton per metre2.

  • Due to this high temperature and pressure,Nuclear fusion reaction is there and a lot of energy emits there.

  • 86 × 1026 joule energy is emitted from the sun per second.The sun energy comes to the earth in the form of Electro magnetic waves.This energy is said to be solar energy.


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