In a medium the speed of light wave decreases to 0.2 times to its speed in free space The ratio of relative permittivity to the refractive index of…

In a medium the speed of light wave decreases to $\displaystyle 0.2$ times to its speed in free space The ratio of relative permittivity to the refractive index of the medium is $\displaystyle x: 1$. The value of $\displaystyle x$ is $\displaystyle \_\_\_\_$. (Given speed of light in free space $\displaystyle =3 \times 10^8 \mathrm{~m} \mathrm{~s}^{-1}$ and for the given medium $\displaystyle \mu_{\mathrm{r}}=1$ )