Discuss in detail the domain theory of ferromagnetism.

Draw a neat sketch of a cycle of magnetisation ($\mathrm{B}-\mathrm{H}$ loop/hysteresis loop) and explain the following terms :

Magnetic saturation

Residual magnetisation (retentivity)

Coercive force

Hysteresis.

Draw a neat sketch of a cycle of magnetisation ($\mathrm{B}-\mathrm{H}$ loop/hysteresis loop) and explain the term: residual magnetisation (retentivity).

Draw a neat sketch of a cycle of magnetisation ($\mathrm{B}-\mathrm{H}$loop/hysteresis loop) and explain the term coercive force.

Draw a neat sketch of a cycle of magnetisation ($\mathrm{B}-\mathrm{H}$ loop/hysteresis loop) and explain the following terms :

hysteresis.

Derive the relation,

$\chi =\left({\mu }_r-1\right)$

where $\chi$ is magnetic susceptibility and ${\mathrm{\mu }}_{\mathrm{r}}$ is relative permeability. Show that

$1$ oersted $= 80$ ampere/metre