Define impedance and its effect on current in an AC circuit.

• A. Impedance is the total opposition to current; current is I = V / |Z|.
• B. Impedance is only resistance; current is I = V / R.
• C. Impedance is purely reactive; current is I = V / X.
• D. Impedance has no effect on current.

Answer: (A)

Impedance is the total opposition to current in an AC circuit, combining resistance and reactance into a single quantity Z = R + jX, where X = X_L − X_C. This complex impedance tells us both how big the current will be and how it will relate in phase to the voltage. For a given applied voltage, the current’s magnitude is inversely related to the impedance magnitude: |I| = |V| / |Z|, and the phase difference between voltage and current is set by the angle of Z. If the circuit is mostly resistive, current is in phase with voltage; if it’s inductive, current lags; if capacitive, current leads. This is why impedance controls how much current flows: higher impedance means smaller current for the same voltage. The correct statement reflects impedance as the total opposition and expresses the basic relationship between voltage, current, and impedance. The other ideas treat impedance as only resistance, or only reactive, or say it has no effect on current, which isn’t true.