What term describes the combined resistive and reactive effects in an AC circuit?

• A. Impedance
• B. Current
• C. Resistance
• D. Voltage

Answer: (A)

Impedance describes the combined resistive and reactive effects in an AC circuit. It generalizes resistance by including reactance, which comes from energy storage elements like inductors and capacitors. Impedance is represented as Z = R + jX, where R is resistance and X is reactance (X = X_L − X_C = ωL − 1/(ωC)). The magnitude |Z| tells you how much opposition there is to current, and the phase angle φ = arctan(X/R) shows whether the current lags or leads the voltage. In a purely resistive circuit, X is zero and impedance equals resistance; in a purely reactive circuit, R is zero and impedance is purely imaginary, causing a 90-degree phase shift. Current describes flow, resistance is the real part of opposition, and voltage is the driving force—none alone capture the complete opposition in AC.