SSC JE Electrical Engineering 2014 Set 1 Paper

A B-H curve is use to show the Relationship between Magnetic Flux Density (B) and Magnetic Field Strength (H) for a Particular Material
$\mathit{B}={\mathit{\mu }}_0{\mathit{\mu }}_{\mathit{r}}\mathit{H}$
where ${\mathit{\mu }}_0$ is Permeability of air
${\mathit{\mu }}_{\mathit{r}}$ is Relative permeability
and Relative Permeability of air is 1.
∴ $\mathit{B}={\mathit{\mu }}_0\mathit{H}$
The shape of curve is straight line passing through origin because Magnetic field applied to air and air never structure.