Answer: BωR²/2.
- A BωR²/2
- B BωR²
- C 2BωR²
- D BωR
Correct answer: A. BωR²/2
Explanation: Treating the disc as made of rotating radial rods, the EMF between centre and rim works out to BωR²/2, the same formula as for a single rotating rod of length R about one end.
As a magnet approaches a coil, flux rises steadily and a constant non-zero EMF is induced (Faraday's law). Once the magnet stops moving, flux stays constant and the induced EMF drops to zero - EMF only exists while flux is actively changing.
Concept context
Faraday's and Lenz's laws, motional EMF, self/mutual inductance, eddy currents, and the AC generator - how a changing magnetic flux creates an electric current.