The radiation energy emitted per second by a point source is $100 \,W$. If the efficiency of the source is $4 \%$, then the rms value of the electric field at a distance of $2 \,m$ is [use $\frac{1}{4 \pi \varepsilon_0}=9 \times 10^9$ in $SI$ units].

The amplitude of the electric field in a parallel beam of plane electromagnetic waves of intensity $53.1 \ W \ m^{-2}$ is (Permittivity of free space $\epsilon_0 = 8.85 \times 10^{-12} \ C^2 \ N^{-1} \ m^{-2}$) (in $N \ C^{-1}$)

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

Which of the following is $NOT$ true for electromagnetic waves?

The electric field in a plane electromagnetic wave is given by $\overrightarrow{E} = 200 \cos \left[ (0.5 \times 10^{3} \text{ m}^{-1}) x - (1.5 \times 10^{11} \text{ rad/s}) t \right] \hat{j} \text{ V/m}$. If this wave falls normally on a perfectly reflecting surface having an area of $100 \text{ cm}^{2}$,and the radiation pressure exerted by the electromagnetic wave on the surface is $\frac{x}{10^{9}} \text{ N/m}^{2}$,find the value of $x$.

During the propagation of electromagnetic waves in a medium,