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 has coercivity $4 \times 10^3 \mathrm{Am}^{-1}$. It is placed inside a solenoid of 12 cm length and 60 turns. The current that should be passed through the solenoid to demagnetise, the bar magnet is