 Magnetic reluctance

The magnetic reluctance of a linear section of magnetic circuit is the ratio of the winding's integrated magnetic field intensity to the magnetic flux, with units $\mathrm{A}\mathrm{W}{\mathrm{b}}^{-1}$. For uniform length $\ell$, cross-sectional area $A$, and relative magnetic permeability ${\mu }_r$, $\mathcal{R}=\ell /({\mu }_0{\mu }_{r}A)$. Series sections carrying the same magnetic flux have additive magnetic reluctances, and $NI=\Phi {\sum }_i{\mathcal{R}}_i$.

Magnetic reluctance is a measure of how easily a material can be magnetized or how difficult it is for magnetic lines of force (magnetic flux) to pass through a magnetic circuit. It is analogous to electrical resistance in electrical circuits. While electrical resistance opposes the flow of electric current, magnetic reluctance opposes the flow of magnetic flux.