Question

In an electrical circuit $R$, $L$, $C$ and an a.c. voltage source are all connected in series. When $L$ is removed from, the circuit, the phase difference between the voltage and the current in the circuit is $\pi /3$. If instead, $C$ is removed from the circuit the phase difference is again $\pi /3$. The power factor of the circuit is :

• A. $1$
• B. $\frac{\sqrt{3}}{2}$
• C. $\frac{1}{2}$
• D. $\frac{1}{\sqrt{2}}$

Answer 1

The correct option is A $1$

Hence in resonant circuit,

$tan\varphi =\frac{\sqrt{3}R-\sqrt{3}R}{R}=0$

thus, $\varphi =0$

therefore power factor = $cos\varphi =1$