The relative permittivity of distilled water is $81$. The velocity of light in it will be $....\times 10^{7} \text{ m/s}$. (Given $\mu_{r} = 1$) (in $.33$)

$A$ sky wave with a frequency $55 \, MHz$ is incident on the $D$-region of the Earth's atmosphere at $45^\circ$. The angle of refraction is ......... $^\circ$ (electron density for the $D$-region is $400 \, \text{electrons}/cm^3$).

The electric and the magnetic field,associated with an electromagnetic wave propagating along the $+z$-axis,can be represented by

In a plane electromagnetic wave travelling in free space,the electric field component oscillates sinusoidally at a frequency of $2.0 \times 10^{10} \text{ Hz}$ and amplitude $48 \text{ V m}^{-1}$. Then the amplitude of the oscillating magnetic field is: (Speed of light in free space $= 3 \times 10^8 \text{ m s}^{-1}$)

The ratio of the magnitudes of the electric field to the magnetic field of an electromagnetic wave is of the order of

The $rms$ value of the electric field of the light coming from the Sun is $720 \; N/C$. The average total energy density of the electromagnetic wave is