The definition of voltage as work per unit charge lends itself very conveniently to the introduction of power. Recall that power is defined as the work done per unit time. Thus, the power P either generated or dissipated by a circuit element can be represented by the following relationship:
The electric power generated by an active element, or that dissipated or stored by a passive element, is equal to the product of the voltage across the element and the current flowing through it.
It is easy to verify that the units of voltage (joules per coulomb) times current (coulombs per second) are indeed those of power (joules per second, or watts).