Question

In an AC series circuit, the instantaneous current is zero when the instantaneous voltage is maximum. Connected to the source may be a

(a) pure inductor
(b) pure capacitor
(c) pure resistor
(d) combination of an inductor and a capacitor

Answer 1

(a) pure inductor
(b) pure capacitor
(d) combination of an inductor and a capacitor.

For a pure inductive circuit, voltage leads the current by $90°$. So, the instantaneous current is zero when the instantaneous voltage is maximum.
Similar is the case with a purely capacitive circuit, in which, current leads the voltage by $90°$.

Also, in a circuit containing a combination of inductor and capacitor, the current may lead or lag the voltage by $90°$, depending upon whether the voltage across the inductor or the capacitor is greater. Here too, there is a phase difference of $90°$ between the voltage and current. Hence, the the instantaneous current is zero when the instantaneous voltage is maximum.