SSC JE Electrical Engineering 2017 Set 1 Paper

$\mathit{S}=\frac{\mathit{l}}{\mathit{\mu }\mathit{A}}$$\mathit{\mu }={\mathit{\mu }}_{\mathit{o}}{\mathit{\mu }}_{\mathit{r}}$
µ = permeability
${\mathit{\mu }}_{\mathit{o}}$ = permeability of vacuum
${\mathit{\mu }}_{\mathit{r}}$ = relative permeability
l = length
A = cross section area
So reluctance of magnetic circuit depend on nature of magnetic material, length of magnetic flex path and cross section area of the material.