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Asked in GSEB Board March 2020 (old course) · Flux change and induced EMF
Given: the magnet approaches the coil with velocity v, inducing emf ε; the coil then also moves away from the magnet with the same velocity v.
Idea: the induced emf depends on the rate of change of flux through the coil, which depends only on the relative motion of magnet and coil.
Both now move in the same direction with the same velocity, so their relative velocity is v - v = 0.
The gap between magnet and coil stays constant, so the flux through the coil does not change.
Induced emf = 0.
So the induced emf is zero. (Had the coil moved towards the magnet, the relative speed would be 2v and the emf 2ε.)
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