Electricity

Electric Power

Rate of doing work is called power. In other words capacity of doing work is power.

Or, Power = Work done/Time

Let 'W' work is done in time 't'

Therefore, P = W/t

SI Unit of Power

SI unit of power is Watt. Watt is denoted by letter 'W'. This got its name in the honour of James Watt, inventor of steam engine.

SI unit of work done is joule and SI unit of time is second.

Thus, if 1 joule of work is done in 1 second

Therefore, 1W = 1 Joule/1sec

Thus, W = joule/second

To express bigger unit of power kilowatt is used. Kilowatt is written as 'kW'

1000 watt(W) = 1 kilowatt (kW)

Or, 1 kW = 1000 W

Electric Power

Electric is a form of energy. Similar to every energy; electricity also has power which ensures its capacity of doing work.

When electric current flows through a conductor, some work is done.

The rate of doing electric work by electric current is called electric power.

This means Electrical Power is the rate of consumption of electrical energy.

If 'W' work is done in time 't'

Therefore, Electric power P = W/t

Let work 'W' is done due to flow of electric current I in time t. Let the potential difference is V during this work done,

Therefore, W = V x I x t joules

Where P = power

V = potential difference

I = electric current

This means

Electric power = Potential difference X Electric current

If electric current = 1 A and potential difference = 1V

Therefore, 1watt = 1V x 1A

Or, 1W = 1VA

This means that 1 watt of electric power is consumed when an electric device takes 1 ampere of electric current having potential difference equal to 1V across the electric circuit.

Different forms of expression of power

We know that,

P = VI --------(1)

Thus, electric power can be defined by using three forms of expressions.

SI unit of electrical power

SI unit of electrical power is 'watt' and is expressed as 'W'

Since, electrical energy is the product of power and time.

Thus, unit of electric energy is 'watt hour'.

Watt hour is written as "Wh"

One watt hour is the energy consumed when 1 watt of power is used for 1 hour.

Commercial unit of electric energy is kilowatt hour

Kilowatt hour is written as "kW h".

1kW h = 1000 watt x 3600 second

= 3.6 x 10 ⁶ watt second

= 3.6 x 10 ⁶ joule (J)

Commercial unit of electric energy (kW h) is generally called unit.

You can see the use of word unit in your electric bill.