Past exam of the physics 2 paper of the University of Oxford / 2014 resit / 9 / a / Solution

The source diagram has $2R$ in series with two parallel branches: $R+L$ above and $R+C$ below. With $s=\sqrt{15}$, their complex impedances are $Z_{+}=R(1+is)$ and $Z_{-}=R(1-is)$. Their parallel combination isThusThe input electric current is in phase with $V_{AB}$ even though the two branch currents separately have nonzero, opposite phase shifts.