Linemen Institute Practice Test

In AC circuits, what does the power factor cosφ represent?

The ratio of reactive power to total power.

The ratio of real power to apparent power.

The cosine of the phase angle between voltage and current.

Power factor is the cosine of the phase angle between the voltage and current in an AC circuit. That phase angle φ exists because reactive elements cause voltage and current to peak at different times. The real power, which is the power that actually does useful work, equals VI cosφ, while the apparent power is VI (the product of RMS voltage and current). So the power factor is the ratio P/S, which simplifies to cosφ. When φ is zero, the current and voltage are in phase and the power factor is 1, meaning all the supplied power is real. When φ is 90 degrees, the power factor is 0, meaning no real power is delivered even though current may flow.

The ratio of voltage to current.