Electromagnetic Induction: Falling Magnets

Imagine dropping a bar magnet vertically through a short fat solenoid connected to a sensitive galvanometer. We drop the magnet from a long way away. As the magnet falls it accelerates, getting closer to the coils, thus inducing an increasing EMF across the ends. When the magnet is in the solenoid, the flux cut by the leading pole of the magnet is opposed by the flux cut by the lagging pole so the EMF will first fall to zero then begin to be generated in the opposite direction, becoming a maximum as the leading edge leaves the coil on the way down. The EMF will fall to zero as the magnet accelerates beyond the coil and the flux linkage weakens. Notice the area of the leading edge and lagging edges are the same – a consequence of energy conservation.

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