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?
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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