A magnet is suspended in the magnetic meridian with an untwisted wire. The upper end of wire is rotated through 180° to deflect the magnet by 30° from magnetic meridian. When the magnet is replaced by another magnet, the upper end of wire is rotated through 270° to deflect the magnet 30° from magnetic meridian. The ratio of magnetic moments of magnets is :-
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Question

A magnet is suspended in the magnetic meridian with an untwisted wire. The upper end of wire is rotated through 180° to deflect the magnet by 30° from magnetic meridian. When the magnet is replaced by another magnet, the upper end of wire is rotated through 270° to deflect the magnet 30° from magnetic meridian. The ratio of magnetic moments of magnets is :-

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G1 Physics · Accepted Answer

At equilibrium, torsion torque Cφ equals MBₕ sin 30°. The lower-end magnet deflection is 30°, so wire twists are 180°−30°=150° and 270°−30°=240°. Thus M₁/M₂=150/240=5/8. Hence C.