$A$ $27\, mW$ 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 $c = 3 \times 10^8\, m/s$]

The layer of the atmosphere that reflects low frequency $(LF)$ electromagnetic waves during day time only is

The speed of an electromagnetic wave in a vacuum depends upon the source of radiation.

$A$ point source of electromagnetic radiation has an average power output of $800\,W$. The maximum value of the electric field at a distance of $3.5\,m$ from the source will be.....$V/m$.

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:

If the magnetic field of a plane electromagnetic wave is given by $B = 5 \times 10^{-6} \sin (0.6 \times 10^2 x + 0.5 \times 10^{10} t)$,then the speed of the wave is