An inductor of inductive reactance $R$, a capacitor of capacitive reactance $2 R$ and a resistor of resistance $R$ are connected in series to an AC source. The power factor of the series $L-C-R$ circuit is

An inductor and a resistor are connected in series to an AC source of 10 V . If the potential difference across the inductor is 6 V , then the potential difference across the resistor is

In a series $L-C-R$ circuit, if the current leads the source voltage, then