The work done in turning a magnet of magnetic moment M by

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The work done in turning a magnet of magnetic moment M by an angle of 90° from the meridian, is n times the corresponding work done to turn it through an angle of 60°. The value of n is given by

1. 2
2. 1
3. 0.5
4. 0.25

Correct Option: A

Magnetic moment = M; Initial angle through which magnet is turned (θ₁) = 90º and final angle through which magnet is turned (θ₂)= 60º. Work done in turning the magnet through 90º(W₁) = MB (cos 0º – cos 90º) = MB (1–0) = MB.
Similarly, W₂ = MB (cos 0º – cos 60º)

∴W₁ = 2W₁ or n = 2.