What term describes the total opposition to AC current that includes resistance and reactance?

• A. Impedance
• B. Admittance
• C. Conductance
• D. Reactance

Answer: (A)

In AC circuits, the total opposition to current isn’t just resistance; it combines resistance with reactance. The combined quantity is impedance. It’s a complex value Z = R + jX, where R is the resistance (real part) and X is the reactance (imaginary part). The magnitude |Z| = sqrt(R^2 + X^2) tells you how much voltage is needed for a given current, and the phase angle φ = arctan(X/R) shows how far the current lags (inductive) or leads (capacitive) the voltage. Reactance itself comes from energy-storage elements: inductors contribute X_L = ωL (positive), capacitors contribute X_C = 1/(ωC) (negative), with net reactance X = X_L − X_C. Admittance, the reciprocal of impedance, describes ease of current flow, with its own real and imaginary parts, but the term that describes the overall opposition including both resistance and reactance is impedance.