$A$ radio can tune into any station in the $6 \text{ MHz}$ to $12 \text{ MHz}$ band. What is the corresponding wavelength band? ( $c = 3 \times 10^{8} \text{ m/s}$ )

An electromagnetic wave of frequency $1 \times 10^{14} \,Hz$ is propagating along the $z$-axis. The amplitude of the electric field is $4 \,Vm^{-1}$. What is the energy density of the electric field? (Permittivity of free space $\varepsilon_0 = 8.8 \times 10^{-12} \,C^2 \,N^{-1} \,m^{-2}$)

For plane electromagnetic waves propagating in the positive $Z$-direction,the combination which gives the correct possible direction for $\vec{E}$ and $\vec{B}$ fields respectively is:

In a plane electromagnetic wave,the electric field oscillates sinusoidally at a frequency of $2.0 \times 10^{10} \; Hz$ and amplitude $48 \; V m^{-1}$.
$(a)$ What is the wavelength of the wave?
$(b)$ What is the amplitude of the oscillating magnetic field?
$(c)$ Show that the average energy density of the $E$ field equals the average energy density of the $B$ field. $[c = 3 \times 10^{8} \; m s^{-1}]$.

Methane is a greenhouse gas because

The refractive index of the ionosphere is ........