Past exam of the physics 2 paper of the University of Oxford / 2017 resit / 10 / d / Solution

In the chosen phasor convention, output phase minus input phase isThe real part of the denominator is positive, so this principal arctangent is continuous throughout the positive-frequency range. Below ${\omega }_0$, the output leads the input, approaching $+\pi /2$ at low frequency. Above ${\omega }_0$, it lags, approaching $-\pi /2$ at high frequency. At the maximum,The input and output are in phase there, with the positive one-third voltage ratio found above.