Past exam of the physics 2 paper of the University of Oxford / 2014 / 5

With phasors proportional to $e^{i\omega t}$, the series RLC circuit hasFor fixed $V_0$ and frequency-independent positive $R$, the maximum occurs when the reactances cancel. ThusThis is the driven current resonance; a damped free-oscillation frequency is a different quantity.

Define the phase difference as current phase minus voltage phase. Since $\tilde{I}=\tilde{V}/Z$,It decreases continuously from $+\pi /2$ at low frequency, through zero at ${\omega }_0=1/\sqrt{LC}$, to $-\pi /2$ at high frequency. Thus the current leads in the capacitive limit and lags in the inductive limit. Defining voltage phase minus current phase would reverse the graph's sign.