If c is the speed of Electromagnetic Waves in vacuum, its speed in a medium of dielectric constant K and relative permeability $\mu$, is

$v=\frac{1}{\mu_r, K}$ $v = c\sqrt{\mu_{rc}K}$ $v=\frac{c}{\sqrt{\mu_r, K}}$ $v=\frac{K}{\mu_r, c}$

$v=\frac{c}{\sqrt{\mu_r, K}}$

$ V = \frac{c}{\eta}$ $\eta = \sqrt{k\mu}$ $\Rightarrow v = \frac{c}{\sqrt{K\mu}}$