The nature of electromagnetic waves is .......

The frequency of an electromagnetic wave is $3 \, MHz$. If the refractive index of the medium is $n = 4$,what happens to the wavelength and frequency when it passes through the medium?

Consider an electromagnetic wave propagating in a vacuum. Choose the correct statement.

An electromagnetic wave of frequency $5\, GHz$ is travelling in a medium whose relative electric permittivity and relative magnetic permeability both are $2$. Its velocity in this medium is $\times 10^{7}\, m/s$.

If $\overrightarrow{E}$ and $\overrightarrow{B}$ represent electric and magnetic field vectors of an electromagnetic wave,the direction of propagation of the electromagnetic wave is along . . . . . . .

To radiate $EM$ signal of wavelength $\lambda$ with high efficiency,the antennas should have a minimum size equal to