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 $I=I_0\sin (\omega t+\varphi )$,
we get $\varphi =\frac{\pi }{2}$
It means that current is ahead of emf by $\frac{\pi }{2}$ rad.