From the definition of potential difference, V, we have V = W/Q, where W is the work done by charge Q. Hence, W = VQ.
Current is the flow of charge, so that in time t, the amount of charge moving through the conductor will be Q = It.
Therefore, W = VIt gives the work done in time t, by a current I, flowing through a conductor across which the potential difference is V. This may be written in two other ways by substituting from Ohm's Law:
where R is the resistance of the conductor.
Remember that power is defined as the rate at which work is done:
By substituting from W = VIt, we obtain the formula for the power dissipated in an electric circuit, as follows:
This formula gives the power which is dissipated when a current I moves through a conductor across which there is a potential difference V.
From Ohm's law we may also write
The unit of power is the WATT, W which is equivalent to one joule per second, J.s-1.