Above the Curie temperature,the susceptibility of a ferromagnetic substance varies

Steel is preferred over soft iron for permanent magnets because

The materials suitable for making electromagnets should have

The relation $H \propto I$ and the susceptibility $\chi = \frac{I}{H}$ are not applicable for which of the following substances?

$A$ thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on,the diamagnetic rod is pushed up,out of the horizontal magnetic field. Hence,the rod gains gravitational potential energy. The work required to do this comes from:

Explain quantitatively the order of magnitude difference between the diamagnetic susceptibility of ${N_2} \left( { \sim 5 \times {{10}^{ - 9}}} \right)$ (at $STP$) and ${Cu} \left( { \sim {{10}^{ - 5}}} \right)$.