Question

In an AC series circuit, the instantaneous current is zero when the instantaneous voltage is maximum.

Answer 1

The device is inductor. In a inductor, the current lags the voltage by a phase difference of 90 degrees.

Hence, when a sinusoidal voltage is applied to an inductor, the voltage leads the current by one-fourth of a cycle, or by a 90º phase angle. Current lags behind voltage, since inductors oppose change in current. Changing current induces an emf. This is considered an effective resistance of the inductor to AC.