What causes the couple acting on the needle of a compass?

$A$ steel wire of length $l$ and magnetic moment $M$ is bent into a semicircular arc of radius $R$. The new magnetic moment is

$A$ cylindrical magnetic rod has length $5 \ cm$ and diameter $1 \ cm$. It has uniform magnetization $M = 5.3 \times 10^{3} \ A/m$. Its net magnetic dipole moment is nearly (take $\pi = 22/7$):

The magnetic dipole moment of a short magnetic dipole at a distant point along the equator of the magnet has a magnitude of $X$ in $SI$ units. If the distance between the point and the magnet is halved,then the magnitude of the dipole moment will be

An iron bar of length $L$ has a magnetic moment $M$. It is bent at the middle of its length such that the two arms make an angle of $60^{\circ}$ with each other. The magnetic moment of this new magnet is:

$A$ magnetised wire of magnetic moment $M$ is bent into an arc of a circle subtending an angle of $60^{\circ}$ at the center. The new magnetic moment is: