Power relations in AC circuits:
For a DC circuit, the power is given by
The power at any instant in an AC circuit is called instantaneous power. It is defined by the product of voltage and current at that instant, i.e.
p = vi
As the voltage and current are not constant in an AC circuit, the power value will also change with time. Therefore, the average power taken over a period T is
The average power is also called the active power or true power and is measured in watts (W). The bigger units are kilowatts (kW) and megawatts (MW).
