What is meant by electric power? Obtain a formula for it. State units of electric power.

Explanation

Power is the rate of doing work.
When work is done, an equal amount of electric energy is consumed. Hence,
"The rate at which electric energy is consumed or dissipated is called electric power."
IF W is the amount of electric energy consumed in a circuit in time t (second), then electric power is given by
`P = W/t ......(12.17)`
But, the electric energy supplied by a current - source in time t is
W =VQ
`:.P = (WQ)/t`
Now,, current `I +Q/t`
`:. P =IV .......(12.18)`
FromOhm.s law V = IR
So,P = (IR) I
`:. P = I^2 R .......(12.19)`
Again from the Ohm.s law `I = V/R`
So, `P = (V/R)^2R`
`:. P = V^2/R` ... ...(12.20)
The SI unit of electric power is the watt (W).
Hence, from equation (12.18),
watt = volt `xx` ampere
Thus, 1 W = 1 volt `xx` 1 ampere = 1 VA
Definition of the SI unit of power: Electric power consumed by a device is said to be 1 W if it carries 1 A of current when operated at a potential difference of 1 V
OR
Electric power of an electric device is 1 watt if it consumes 1 joule of electric energy in 1 second.