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A bar magnet of length 'ℓ' and magnetic dipole moment 'M' is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be

1. (a) 3/π M
2. (b) 2/π M
3. (c) M/2
4. (d) M

Correct answer: (b) 2/π M

Solution

When the bar magnet is bent into an arc, its magnetic dipole moment is proportional to the effective length of the arc. The effective length of the arc is reduced to 2/π of the original length, so the new magnetic dipole moment becomes 2/π times the original dipole moment.

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