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].

What is the value of the speed of light in free space?

Suppose that the electric field part of an electromagnetic wave in vacuum is $E = \{(3.1 \; N/C) \cos [(1.8 \; rad/m) y + (5.4 \times 10^{6} \; rad/s) t] \} \hat{i}$.
$(a)$ What is the direction of propagation?
$(b)$ What is the wavelength $\lambda$?
$(c)$ What is the frequency $\nu$?
$(d)$ What is the amplitude of the magnetic field part of the wave?
$(e)$ Write an expression for the magnetic field part of the wave.

An $EM$ wave from air enters a medium. The electric fields are $\overrightarrow {{E_1}} = {E_{01}}\hat x\cos[2\pi v(\frac{z}{c} - t)]$ in air and $\overrightarrow {{E_2}} = {E_{02}}\hat x\cos[k(2z - ct)]$ in medium,where the wave number $k$ and frequency $v$ refer to their values in air. The medium is nonmagnetic. If $\varepsilon_{r_1}$ and $\varepsilon_{r_2}$ refer to relative permittivities of air and medium respectively,which of the following options is correct?

Given below are two statements: one is labelled as Assertion $(A)$ and other is labelled as Reason $(R).$
Assertion $(A):$ Electromagnetic waves carry energy but not momentum.
Reason $(R):$ Mass of a photon is zero.
In the light of the above statements,choose the most appropriate answer from the options given below:

$A$ $27\, mW$ laser beam has a cross-sectional area of $10\, mm^2$. The magnitude of the maximum electric field in this electromagnetic wave is given by: $........\, kV/m$. [Given permittivity of free space $\epsilon_0 = 9 \times 10^{-12}\, SI\, units$, speed of light $c = 3 \times 10^8\, m/s$]