In an ac circuit, the instantaneous current is zero, when the instantaneous voltage is maximum. In this case, the source may be connected to: A. pure inductor. B. pure capacitor. C. pure resistor. D. combination of an inductor and capacitor. Choose the correct answer from the options given below :

In an AC circuit, the instantaneous current is zero when the instantaneous voltage is maximum. This implies a 90-degree phase difference between voltage and current. We need to identify which circuit elements produce this behavior.

Recall: If $$V = V_0\sin(\omega t)$$ and $$I = I_0\sin(\omega t \pm 90°)$$, then when $$V$$ is at maximum ($$\sin(\omega t) = 1$$), $$I = I_0\sin(\omega t \pm 90°) = \pm I_0\cos(\omega t) = 0$$ (at the same instant).

A. Pure inductor: In a pure inductor, current lags voltage by 90°: $$I = I_0\sin(\omega t - 90°)$$. When voltage is maximum, current is zero. YES.

B. Pure capacitor: In a pure capacitor, current leads voltage by 90°: $$I = I_0\sin(\omega t + 90°)$$. When voltage is maximum, current is zero. YES.

C. Pure resistor: In a pure resistor, current and voltage are in phase: $$I = I_0\sin(\omega t)$$. When voltage is maximum, current is also maximum (not zero). NO.

D. Combination of inductor and capacitor (LC circuit): In a pure LC circuit (no resistance), the impedance is purely reactive: $$Z = j(\omega L - \frac{1}{\omega C})$$. The current either leads or lags the voltage by exactly 90°. Therefore, when voltage is maximum, current is zero. YES.

The correct answer is Option (4): A, B and D only.