Magnetism and matter practice · Medium

Option D ($MH\left( {1 - \cos \mathrm{\theta }} \right)$) is correct because it represents the work done in rotating a magnetic dipole in a magnetic field.

Option D (Ferromagnetic changes to paramagnetic) is correct because above the Curie temperature, ferromagnetic materials lose their spontaneous magnetization and become paramagnetic.

Option B ($Q$ is a bar magnet identical to $P$, and its north pole is placed on top of $P$'s north pole) is correct because the time period remains unchanged, implying the effective magnetic moment doubles, which only happens when identical magnets are aligned.

Option C is correct. Diamagnetic materials have a small negative susceptibility, not a positive one.

Option D (One) is correct because when a magnet is placed vertically, there is only one neutral point on the horizontal board, which lies on the equatorial line.

Option A (If both (A) and (R) are true and the (R) is a correct explanation of the (A)) is correct because the time period is inversely proportional to the magnetic moment, which is greater in the sum position.

Option A (30$^ \circ$) is correct because the magnetic field due to a short magnet varies inversely with the cube of the distance.

Option A is correct because the direction of magnetic moment and orbital angular momentum are opposite for an electron due to its negative charge, making the reason a correct explanation.