If the relative permeability and dielectric constant of a medium are $\mu_r$ and $K$ respectively,then the refractive index $n$ of the medium is:

Which of the following do not require a medium for transmission?

You are driving in your car listening to music on the radio. Your car is equipped with a radio that can receive radio signals of frequency $(f_1 \approx 3 \, MHz)$,$(f_2 \approx 30 \, MHz)$,and $(f_3 = 3 \, GHz)$. You enter a tunnel with a circular opening of diameter $10 \, m$. Which kind of radio signal will you be able to receive for the longest distance as you continue to travel in the tunnel?

$A$ plane electromagnetic wave of frequency $100 \, MHz$ is travelling in vacuum along the $x$-direction. At a particular point in space and time,$\overrightarrow{B} = 2.0 \times 10^{-8} \hat{k} \, T$ (where $\hat{k}$ is the unit vector along the $z$-direction). What is $\overrightarrow{E}$ at this point?

The refractive index of the ionosphere is

The layer of the atmosphere that reflects low frequency $(LF)$ electromagnetic waves during day time only is