Magnetism Questions

Electromagnets are made of soft iron because soft iron has:

A thin ring of radius $R\text{ meter}$ has charge $q\text{ coulomb}$ uniformly spread on it. The ring rotates about its axis with a constant frequency of $f\text{ revolutions/s}$. The value of magnetic induction in ${\text{Wb/m}}^2$ at the centre of the ring is:

Two identical long conducting wires $AOB$ and $COD$ are placed at right angle to each other, with one above other such that '$O$ ' is their common point. The wires carry $I_1$ and $I_2$ currents, respectively. Point '$P$ ' is lying at distance '$d$ ' from '$O$ ' along a direction perpendicular to the plane containing the wires. The magnetic field at point '$P$ ' will be:

If a diamagnetic substance is brought near the north or the south pole of a bar magnet, it is:

A bar magnet having a magnetic moment of $2\times 10^4{\text{JT}}^{-1}$ is free to rotate in a horizontal plane. A horizontal magnetic field $B=6\times 10^{-4}\text{T}$ exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction $60^{\circ }$ from the field is: