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A bar magnet of magnetic moment M is placed at right angles to a magnetic induction B. If a force F is experienced by each pole of the magnet, the length of the magnet will be

1. (a) F/MB
2. (b) MB/F
3. (c) BF/M
4. (d) MF/B

Correct answer: (b) MB/F

Solution

The force on each pole of the magnet is given by F = mB, where m is the pole strength. The magnetic moment M is related to the pole strength and length of the magnet as M = m × l. Rearranging, l = M/F × B, which simplifies to MB/F.

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