The magnetic susceptibility of a ferromagnetic substance is

$A$ domain in ferromagnetic iron is in the form of a cube of side length $1\; \mu m$. Estimate the number of iron atoms in the domain and the maximum possible dipole moment and magnetisation of the domain. The molecular mass of iron is $55\; g/mol$ and its density is $7.9\; g/cm^3$. Assume that each iron atom has a dipole moment of $9.27 \times 10^{-24}\; A m^2$.

$A$ Rowland ring of mean radius $15\; cm$ has $3500$ turns of wire wound on a ferromagnetic core of relative permeability $800$. What is the magnetic field $B$ (in $T$) in the core for a magnetizing current of $1.2\; A$?

The unit for molar susceptibility is

Oersted is a unit of

The relation between the magnetic susceptibility $\chi$ and the relative magnetic permeability $\mu_r$ is: