In an AC circuit, the power factor is $0.5$. If the phase difference between voltage and current is $60^{\circ }$, the circuit could be:

Solution

1. Power factor is $\cos (\varphi )=0.5$, so $\varphi =60^{\circ }$.
2. Purely resistive circuits have $\varphi =0^{\circ }$.
3. Purely inductive or capacitive circuits have $\varphi =90^{\circ }$.
4. A series RL circuit can have a phase angle between $0^{\circ }$ and $90^{\circ }$.
5. Hence the answer is (C).