A change in magnetic flux linkage with the coil induces an e.m.f.; a greater rate of change of flux linkage gives a larger induced e.m.f. Before the magnet enters, the e.m.f. is zero. As the south pole approaches, the flux linkage changes and a positive e.m.f. is produced. When the south pole reaches the coil, the rate of change of flux linkage becomes zero and the polarity then reverses as the flux linkage decreases, giving a negative e.m.f. The magnet accelerates downwards, so the later peak has a larger magnitude and occurs over a shorter time. The e.m.f. returns to zero when the magnet has completely left the coil.
