Approved Training Organization (ATO) Test 3 Alternating Current (AC) Practice

Reactive power is the part of electrical power that moves back and forth between the source and the reactive elements (inductors and capacitors) without doing net work over a cycle. It is represented by the symbol Q in standard AC theory, as the imaginary component of the complex power S = P + jQ. The active (real) power P relates to voltage and current by P = VI cos φ, while reactive power relates by Q = VI sin φ, where φ is the phase angle between voltage and current. The apparent power magnitude is S = sqrt(P^2 + Q^2), and the sign of Q indicates whether the load is inductive (current lags voltage, positive Q) or capacitive (current leads voltage, negative Q). If your course uses a different letter for reactive power, that’s a labeling choice, but the concept remains tied to the sin φ relationship and the separation of power into real and reactive components.