In an electromagnetic wave,the energy density associated with the magnetic field will be:

$A$ 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 $400 \, \text{electrons}/cm^3$).

In a plane $EM$ wave,the electric field oscillates sinusoidally at a frequency of $5 \times 10^{10} \,Hz$ and an amplitude of $50 \,Vm^{-1}$. The total average energy density of the electromagnetic field of the wave is :
[Use $\varepsilon_0 = 8.85 \times 10^{-12} \,C^2 / Nm^2$ ]

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

About $20 \%$ of the power of a $100 \ W$ bulb is converted to visible radiation. Assuming that the radiation is emitted isotropically and neglecting reflection,the average intensity of visible radiation at a distance of $5 \ m$ is $\frac{\alpha}{25 \pi} \ W/m^2$. The value of $\alpha$ is

When light propagates through a material medium of relative permittivity $\varepsilon_{r}$ and relative permeability $\mu_{r}$,the velocity of light,$v$,is given by: ($c$ = velocity of light in vacuum)