Reactive power in an AC circuit is measured in what units?

• A. Var
• B. Watts
• C. Joules
• D. Volt

Answer: (A)

Reactive power captures the part of power in an AC circuit that is alternately stored and released by inductors and capacitors, not consumed to do work. It reflects the energy bouncing between the source and the reactive elements as the current and voltage are out of phase. The right way to express that rate of energy exchange is in volt-amps reactive (VAR). The math, Q = V_rms I_rms sin(phi), shows how the phase angle between voltage and current determines reactive power. In contrast, real power (watts) is the portion that actually does useful work, given by P = V_rms I_rms cos(phi). Energy over time is measured in joules, and voltage itself is measured in volts. So reactive power is measured in VAR.