Electrical power:

Electrical power (symbol P) is the rate at which work is done or the rate of conversion of energy by an electrical system.

The SI unit of power is the watt which is a rate of work of 1 joule per second.

                   Therefore           P  =  V  *  I        

                   That is                watts  =  volts  *  amps

By substituting V  =  IR in the above formula, two other expressions for electrical power are obtained:

                                      P  =  VI  =  I²R  =  V^2/R  watts