A bar magnet falls vertically from rest through a coil of wire. The potential difference (pd) across the coil is recorded by a datalogger.

The graph shows the variation with time of the pd across the coil.

(a) (i) Explain, with reference to Faraday’s and Lenz’s laws, the shape of the graph. 

(a) (ii) The coil has 1500 turns. Calculate the magnitude of the maximum rate of change of magnetic flux.

The magnet is now suspended from a spring. The magnet is displaced vertically and starts to oscillate in and out of the coil. A sinusoidal alternating current of rms value 280nA is induced in the coil.

(b) (i) State in words how the rms value of the alternating current relates to a direct current of 280 nA.

(b) (ii) The coil has a resistance of 1.5M ohm. Calculate the peak voltage across the coil.

(b) (iii) Explain what effect the generation of the current has on the oscillation of the magnet.