Electromagnetism - Electric Power

The rate at which electric work is done by the source of in maintaining the current in electric circuit is called electric power of the circuit. 

If a current I ampere flows through a conductor of resistance R for a time t second under a potential difference of V volt then electric work done to maintain the current is given by 

W = Vt joule.

∴ Electric power , P = W / t = VIt / t = VI watt or Js ^{- 1} 

Power (in watt) = V (in volt) x 1 ( in ampere)

If, V = 1V 
 
And I = 1 A 
 
Then p = 1 watt.

∴ 1 watt = 1 V x 14 = 1 ampere-volt

Thus the power of an electric circuit is said to be one watt if one ampere current flows in it against a potential difference of 1 volt.

Bigger units of power are kilowatt (KW) and mega watt (MW).

Where 1 kW = 1000W

And 1 MW = 106 W.

Commercial unit of power is horse power (H.P) where 1 HP = 746 watt.

As V = IR or I = V / R, so

P = VI = I₂R = V₂/R

The source of this power is an external source to keep a steady current through the conductor. In a simple circuit where the current is supplied to a conductor by the cells, it is the chemical energy of the cells which supplies this power for as long as it can.

A bulb of 484 O is producing light when connected to 220 V supplies what is the electric power of a bulb?

Electric power 

P = V₂ /R = (220)² / 484 = 100 watt.

How much current is drawn by the motor of 0.5 H.P from 220 volt supply?

P = 0.5 H.P = 0.5 x 746 watt 

I = p / V = 0.5 x 746 / 220 = 1.7A


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