Power in AC Circuit: The Power Factor

For a DC circuit the power is P=VI, and this relationship also holds for theinstantaneous power in an AC circuit. However, the average power in an AC circuit expressed in terms of the rms voltage and current is.

Pavg =VI cos Ø

where Ø is the phase angle between the voltage and current. The additional term is called the power factor.

Power Factor = cosØ = R/Z