The flow of electric current in any circuit causes electric energy. Like, an electric bulb converts electrical energy into light energy, Electric fan converts electric energy into mechanical energy, Radio set converts electrical energy into sound energy.
We know that work done in flowing the charge q through a conductor having potential difference V,
W = q V
= (I t) (R I), as q= I t and V= R I
W = I2 R t
This work is the measure of electric energy supplied by any electric source like a cell, battery or mains. Therefore, electrical energy produced by a conductor of resistance R ohm carrying the current I ampere for time t second is equal to E = I2 R t joule (J).
In this electrical energy, can be converted into any other form of energy like heat, sound, light, or mechanical energy.
We know that rate of doing work is power. Therefore, electric power,
= I2 r t/ t
P = I2 R watt(W)