What is the power factor of a system or circuit?

• A. the ratio of true power to apparent power
• B. the ratio of impedance to reactance
• C. the relationship of volts and ohms
• D. none of the above

Answer: (A)

Power factor tells you how effectively electrical power is converted into useful work. It is the ratio of true (real) power to apparent power. Real power, measured in watts, is the actual work done by resistive components. Apparent power, measured in volt-amperes, is the product of the RMS voltage and RMS current and represents the total power flow, including energy that’s alternately stored and released by reactive elements like inductors and capacitors. The power factor equals cos(phi), where phi is the phase angle between voltage and current; when voltage and current are in phase (no reactive power), the power factor is 1. Any reactive power reduces the power factor below 1. So the statement about the ratio of true power to apparent power correctly defines power factor. The other ideas—ratio of impedance to reactance or the basic voltage-to-resistance relationship—do not capture what power factor measures.