If $ε_0$ and $\mu_0$ represent the permittivity and permeability of vacuum and ε and $\mu$ represent the permittivity and permeability of medium, then refractive index of the medium is given by

$\sqrt{\frac{\mu_0ε_0}{\mu ε}}$ $\sqrt{\frac{\mu ε}{\mu_0ε_0}}$ $\sqrt{\frac{\mu }{\mu_0ε_0}}$ $\sqrt{\frac{\mu_0ε_0}{\mu }}$

$\sqrt{\frac{\mu ε}{\mu_0ε_0}}$

Refractive index $ = \frac{c}{v}=\frac{1/\sqrt{\mu_0ε_0}}{1/\sqrt{\mu ε}}$ $=\sqrt{\frac{\mu ε}{\mu_0ε_0}}$