Answer: connect the rotating coil to the outer circuit.
- A steadily strengthen the magnetic field
- B lower the resistance of the coil winding
- C periodically reverse the magnetic field
- D connect the rotating coil to the outer circuit
Correct answer: D. connect the rotating coil to the outer circuit
Explanation: Slip rings maintain continuous electrical contact with the rotating coil and transfer the generated alternating emf to the external circuit.
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.