Power in an A.C Circuit

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When an alternating current flows in a resistance, the power dissipated can be calculated as follows:

P = IV =  I² R

Power dissipation in an inductor and capacitor is zero, meaning they do not dissipate any energyEnergy is the ability to do work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, and electrical energy. Units of Energy: The SI unit... More as heat; they only store energy in their magnetic field (inductor) or electric field (capacitor) when connected to an AC power source. 

Inductors and capacitors return the energy they store to the circuit when the current changes direction, leading to no net power loss.

V sin φ is the voltage across total inductance and capacitance where power is zero, the horizontal component voltage is in phase with the current I, which gives the useful power in the circuit, Cos φ. Cos φ is therefore called the power factor.

Therefore, P = IV cos φ

In a purely inductive or capacitive circuit, the current is 90 degrees out of phase with the voltage. This results in a