$A$ laser beam of pulse power $10^{12} \ W$ is focused on an object area of $10^{-4} \ cm^2$. The energy flux in $W/cm^2$ at the point of focus is:

The magnetic field in a plane electromagnetic wave is given by
$B_y = (2 \times 10^{-7}) \sin (0.5 \times 10^3 x + 1.5 \times 10^{11} t) \, T$
$(a)$ What is the wavelength and frequency of the wave?
$(b)$ Write an expression for the electric field.

When $\mu_r$ and $\epsilon_r$ are the relative permeability and relative permittivity (dielectric constant) respectively,the refractive index is given by:

The refractive index of the ionosphere is

Which of the following pairs of components can produce a plane electromagnetic wave propagating in a direction such that the electric field $\vec{E} = (E_x\hat{i} + E_y\hat{j} + E_z\hat{k})$ and magnetic field $\vec{B} = (B_x\hat{i} + B_y\hat{j} + B_z\hat{k})$ vary with position and time?

The unit of $\sqrt{\frac{2 I}{\varepsilon_0 c}}$ is
($I$: intensity of an electromagnetic wave,$c$: speed of light)