Two short bar magnets with magnetic moments 400 ab-amp $\mathrm{c}{\mathrm{m}}^2\mathrm{ }$and 800 ab-amp $\mathrm{c}{\mathrm{m}}^2\mathrm{ }\mathrm{a}\mathrm{r}\mathrm{e}$ placed with their axis in the same straight line with similar poles facing each other and with their centers at 20 cm from each other. Then the force of repulsion is

A rectangular loop of sides $10 \mathrm{cm}$ and $5 \mathrm{cm}$, carrying a current $I$ of $12 \mathrm{A}$, is placed in different orientations as shown in the figure below.
(a)  (b)

(c)  (d)

If there is a uniform magnetic field of $0.3 \mathrm{T}$ in the positive $z$ direction, in which orientations the loop would be in $\left(\mathrm{i}\right)$ stable equilibrium and $\left(\mathrm{ii}\right)$ unstable equilibrium?

A coil of $50$ turns carrying a current of $2\mathrm{A}$ in a magnetic field of $0.5\mathrm{T}$. The torque acting on the coil is

The ratio of the magnetic field at the centre of a current-carrying circular coil to magnetic moment is $x$. If the current and the radius both are doubled. The new ratio will become