Electric power a physical quantity that is equal to the ratio of the work done by the current to the time spent doing it:
$$N=\frac{A}{t}=UI=I^{2}R=\frac{U^{2}}{R}$$
where,
A— work;
I— current intensity;
R— resistance;
U— voltage;
t— time.
Active power characterizes the power that can be converted into useful work or stored as other forms of energy. The unit of active power in the International System of Units (SI) is the watt (symbol W). One watt is equivalent to a power level at which one joule (J) of work is done in one second (s). Electric power is measured using a wattmeter.