# The velocity of electromagnetic radiation in a medium of permittivity $\in_0$ and permeability $\mu_0$ is given by :

$\begin {array} {1 1} (1)\;\sqrt{\large\frac{\mu_0}{\in_0}} & \quad (2)\;\sqrt{\large\frac{\in_0}{\mu_0}} \\ (3)\;\sqrt {\mu_0\: \in_0} & \quad (4)\;\sqrt{\large\frac{1}{\mu_0\: \in_0}} \end {array}$