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

The loop area is $A=\pi (5\times 10^{-3}{)}^2{\mathrm{m}}^2$. Integrating Ohm's law and Faraday's law through the whole decay givesThereforeThe switching time cancels: a faster linear flux decay produces a larger electric current for a proportionally shorter interval. If the coil's self-inductance is retained, integrating $LdI/dt$ gives zero provided the initial and final currents vanish and the stated total charge includes the decay tail.