If ε₀ and μ₀ are the electric permittivity and magnetic permeability of free space and ε and μ are the corresponding quantities in the medium, the index of refraction of the medium in terms of above parameter is

$\left(\frac{ε\mu}{ε_0\mu_0}\right)^{1/2}$

Velocity of light in vacuum

$c=\frac{1}{\sqrt{\mu_0ε_0}}$

velocity of light in medium

$v =\frac{1}{\sqrt{\mu ε}}$

$ ∴ \mu = \frac{c}{v}= \left(\frac{\mu ε}{\mu_0 ε_0}\right)^{1/2}$