Question

If A.C. voltage is applied to a pure capacitor, then voltage across the capacitor _________.

• A. Leads the current by phase angle $\left(\frac{\pi }{2}\right)$ rad.
• B. Leads the current by phase angle $\left(\pi \right)$ rad.
• C. Lags behind the current by phase angle $\left(\frac{\pi }{2}\right)$ rad.
• D. Lags behind the current by phase angle $\left(\pi \right)$ rad.

Answer 1

Answer: (C)

Lags behind the current by phase angle $\left(\frac{\pi }{2}\right)$ rad.

In a capacitor, as the voltage applied is increased, there is current going into the capacitor. Now, as the applied voltage reaches the positive peak, the charging (in flow of current) stops. As the voltage starts to reduce, current flows out of the capacitor and continues until the voltage reaches the negative peak and discharging stops.

If we trace this out on a graph we will see that the current is leading the voltage by 90°, reaching zero current at the peaks of the voltage and maximum current as the voltage is going through zero. Hence, the voltage acrross the capacitor lags behind current by the phase angle $\left(\frac{\pi }{2}\right)$ rad.