In a pure inductive AC circuit, what is the phase relationship between voltage and current?

• A. Current lags voltage by 90 degrees
• B. Current leads voltage by 90 degrees
• C. They are in phase
• D. Current leads voltage by 180 degrees

Answer: (A)

In a pure inductive AC circuit, the current lags the voltage by 90 degrees. This happens because the voltage across an inductor is proportional to the rate of change of current (v = L di/dt). If the applied voltage varies sinusoidally, integrating that voltage over time gives a current that reaches its peak a quarter cycle later than the voltage, i.e., a 90-degree phase shift. The current leading by 90 degrees would describe a capacitor, while in-phase current and voltage would indicate a resistor. A 180-degree relationship would imply an inverted signal, which isn’t the case for a pure inductor.