An electromagnetic wave has a frequency of $3 \text{ MHz}$ in free space. When this wave passes through a medium with a relative permittivity $\varepsilon_r = 4.0$,its frequency will be:

The magnetic field of a plane electromagnetic wave is given by $\vec B = B_0 \hat i \cos(kz - \omega t) + B_1 \hat j \cos(kz - \omega t)$,where $B_0 = 3 \times 10^{-5} \, T$ and $B_1 = 2 \times 10^{-6} \, T$. The rms value of the force experienced by a stationary charge $Q = 10^{-4} \, C$ at $z = 0$ is closest to:

Which one of the following statements is correct?

The biological importance of the ozone layer is that:

$A$ radio station has two channels. One is $AM$ at $1020 \ kHz$ and the other is $FM$ at $89.5 \ MHz$. For good results,you will use:

The pressure exerted by an electromagnetic wave of intensity $I \ (W/m^2)$ on a non-reflecting surface is [$c$ is the velocity of light].