What is apparent power in an AC circuit?

• A. The ratio of true power to voltage.
• B. The phase difference between voltage and current.
• C. The product of circuit voltage and circuit current.
• D. The energy stored in the circuit.

Answer: (C)

In AC circuits, apparent power is the product of the RMS voltage and RMS current, measured in volt-amperes (VA). It represents the total magnitude of power flowing in the circuit, combining both the real power that does useful work and the reactive power that stores and returns energy in inductors and capacitors. The actual power delivered to a load on average is P = V_rms I_rms cosφ, where φ is the phase difference between voltage and current, and the reactive power is Q = V_rms I_rms sinφ. Because voltage and current can be out of phase, the instantaneous power p(t) = v(t)i(t) varies over time, while the RMS product V_rms I_rms gives the overall magnitude of power flow. The energy stored in the circuit isn’t what apparent power measures; that’s described by the reactive relationships and energy exchange in reactive elements. So the correct idea is that apparent power equals the product of circuit voltage and circuit current (using RMS values).