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A bar magnet is moved along the axis of a copper ring that lies far from the magnet. Viewed from the magnet's side, the induced current in the ring is observed to be anticlockwise. Which of the following could be the case?

1. The south pole faces the ring while the magnet moves toward the ring.
2. The north pole faces the ring while the magnet moves toward the ring.
3. The south pole faces the ring while the magnet moves away from the ring.
4. The north pole faces the ring while the magnet moves away from the ring.

Correct answer: The south pole faces the ring while the magnet moves toward the ring.

Solution

As viewed from the magnet, an anticlockwise induced current makes the near face of the ring a magnetic south pole. By Lenz's law the ring must oppose the flux change. A near south face will attract a north pole and repel a south pole. If the south pole of the magnet is approaching (flux into ring from a south face increasing), the ring opposes it by presenting a south pole toward the magnet (repulsion) - consistent with the observed anticlockwise current. Hence: south pole facing the ring and the magnet moving toward it.

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