Question

An alternating emf is applied to purely capacitive circuit. The phase relation between emf and current flowing in the circuit is

• A. emf is ahead of current by $\pi / 2$
• B. current is ahead of emf by $\pi / 2$
• C. current lags behind emf by $ \pi$
• D. current is ahead of emf by $\pi$

Answer 1

Answer: (B)

For a pure capacitance circuit current equation is
$I=\omega C V_{0} \sin (\omega t+\pi / 2)$
Comparing with $I=I_{0} \sin (\omega t+\phi)$,
we get $\phi=\frac{\pi}{2}$
It means that current is ahead of emf by $\frac{\pi}{2}$ rad.