Reactive power is measured in which units?

• A. Watts
• B. VA
• C. VARS
• D. Henry

Answer: (C)

In AC circuits, power comes in three forms: real power that does actual work or heat, reactive power that alternately stores and returns energy in the magnetic or electric fields, and apparent power which is the combination of the two. Reactive power is measured in volt-ampere reactive, written as VARs. This unit distinguishes reactive power from real power, which is measured in watts, and from apparent power, measured in volt-amperes. In calculations, the three quantities relate as S = sqrt(P^2 + Q^2), where S is in VA, P in W, and Q in VARs. The sign of reactive power indicates inductive (positive Q) or capacitive (negative Q) behavior. The other options correspond to real power (watts), apparent power (VA), or inductance (henry), which do not measure reactive power.