The speed of electromagnetic waves is the same for all ........

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 an electromagnetic wave is $1 \ V/m$. The frequency of the wave is $5 \times 10^{14} \ Hz$. The wave propagates along the $z$-axis. What is the average energy density of the electric field in $J/m^3$?

If the magnetic field of a plane electromagnetic wave is given by (The speed of light $c = 3 \times 10^8 \, m/s$):
$B = 100 \times 10^{-6} \sin \left[ 2\pi \times 2 \times 10^{15} \left( t - \frac{x}{c} \right) \right]$
Then the maximum electric field associated with it is:

Suppose that the intensity of a laser is $\left(\frac{315}{\pi}\right) \ W/m^2$. The $rms$ electric field,in units of $V/m$,associated with this source is close to the nearest integer. Given: $\epsilon_0 = 8.86 \times 10^{-12} \ C^2 N^{-1} m^{-2}$ and $c = 3 \times 10^8 \ m/s$.

Show that the radiation pressure exerted by an $EM$ wave of intensity $I$ on a surface kept in vacuum is $\frac{I}{c}$.