If a bar magnet of moment $10^{-4} \mathrm{Am}^2$ is kept in a uniform magnetic field of $12 \times 10^{-3} \mathrm{~T}$ such that it makes angle of $30^{\circ}$ with the direction of magnetic field, then the torque acting on the magnet is

The most exotic diamagnetic materials are

A bar magnet of magnetic moment $2 \mathrm{~A}-\mathrm{m}^2$ lies aligned with the direction of a uniform magnetic field of 0.3 T . The amount of work required by an external torque to turn the magnet so as to align its magnetic moment normal to the field direction is

If $\chi$ is the susceptibility and $\mu_r$ is the relative permeability of a ferromagnetic substance, then