Q 12-08-080JEE MainJEE Main 2023 (31 Jan, Shift 1)Easy
In a medium the speed of light wave decreases to $0.2$ times its speed in free space. The ratio of relative permittivity to the refractive index of the medium is $x:1$. The value of $x$ is ______. (Given speed of light in free space $=3\times10^8\ \text{m s}^{-1}$ and for the given medium $\mu_r=1$)
Numerical value type. Enter your answer.
Answer: 5
$n=\dfrac cv=5$. With $\mu_r=1$, $n=\sqrt{\varepsilon_r}\Rightarrow\varepsilon_r=25$.
$\dfrac{\varepsilon_r}{n}=\dfrac{25}{5}=5$.
Solution by Sreeraj P, M.Sc Physics