In AC circuits, the quantity expressed by volt-amperes corresponds to which of the following?

• A. Apparent Power
• B. Reactive Power
• C. RMS voltage
• D. True Power

Answer: (D)

Volt-amperes quantify apparent power, the total power flow in an AC circuit. In sinusoidal steady state, S equals the product of RMS voltage and RMS current (S = V_rms × I_rms). This magnitude is the complex power S = V × I*, whose real and reactive parts are P = V_rms I_rms cosφ and Q = V_rms I_rms sinφ, with φ the phase angle between voltage and current. The relationship S^2 = P^2 + Q^2 shows that VA combines both the useful power delivered (P) and the power stored and returned by reactive elements (Q). Pure real power in watts equals P, while reactive power is in VAR. When φ = 0, P = S, but in general S > P. Therefore, volt-amperes correspond to apparent power, not true power.