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

An electromagnetic wave of frequency $1 \times 10^{14} \,Hz$ is propagating along the $z$-axis. The amplitude of the electric field is $4 \,Vm^{-1}$. What is the energy density of the electric field? (Permittivity of free space $\varepsilon_0 = 8.8 \times 10^{-12} \,C^2 \,N^{-1} \,m^{-2}$)

The energy density of an electromagnetic wave in a vacuum is given by the relation:

If $c$ is the speed of electromagnetic waves in vacuum,its speed in a medium of dielectric constant $K$ and relative permeability $\mu_r$ is

The Poynting vector $\vec S$ is defined as a vector whose magnitude is equal to the wave intensity and whose direction is along the direction of wave propagation. Mathematically,it is given by $\vec S = \frac{1}{{\mu _0}}(\vec E \times \vec B)$. Show the nature of the $\vec S$ vs $t$ graph.

The speed of electromagnetic radiation in vacuum is