If ${\mathrm{\epsilon }}_0$ and ${\mathrm{\mu }}_0$ are respectively the electric permittivity and the magnetic permeability of free space and $\epsilon$ and $\mu$ the corresponding quantities in a medium, the refractive index of the medium is

• A

  $\sqrt{\left(\frac{\mathrm{\mu \epsilon }}{{\mathrm{\mu }}_0{\mathrm{\epsilon }}_0}\right)}$

• B

  $\frac{\mathrm{\mu \epsilon }}{{\mathrm{\mu }}_0{\mathrm{\epsilon }}_0}$

• C

  $\sqrt{\left(\frac{{\mathrm{\mu }}_0{\mathrm{\epsilon }}_0}{\mathrm{\mu \epsilon }}\right)}$

• D

  $\sqrt{\left(\frac{{\mathrm{\mu \mu }}_0}{{\mathrm{\epsilon \epsilon }}_0}\right)}$