Two small bar magnets are placed in a line with like poles facing each other at a certain distance $d$ apart. If the length of each magnet is negligible as compared to $d$,the force between them will be inversely proportional to

Two short magnets of equal dipole moments $M$ are fastened perpendicularly at their centres,which lie at the origin. Let the two magnets lie along the $X$-axis and $Y$-axis,respectively. The magnitude of the magnetic field at a distance $R$ from the centre on the $Y$-axis is $\frac{\mu_0}{4 \pi} \frac{M_0}{R^3}$. Assuming $R >> l$ (magnet length),the magnitude of $M$ is

The work done in turning a magnet of magnetic moment $M$ by an angle $\theta$ from its initial position parallel to the magnetic meridian is:

The figure shows a bar magnet and a long straight wire $W$,carrying current into the plane of the paper. Point $P$ is the point of intersection of the axis of the magnet and the line of shortest distance between the magnet and the wire. If $P$ is the midpoint of the magnet,then which of the following statements is correct?

$A$ bar magnet of magnetic moment $200 \, A-m^2$ is suspended in a magnetic field of intensity $0.25 \, N/A-m$. The torque required to deflect it through $30^\circ$ is .... $N-m$.

Derive the equation of torque on a magnetic needle in a uniform magnetic field.