Sec 31.4-31.7
The derivation of the wave equation in sec 31.5 is fairly math heavy and
non-essential. The results Eq 31.36-38 are the important takeaways.
Similarly, the beginning of section 31.7 is important but we will not use
Malus's Law.
In the video below, Le and Prof. Leblond illustrate a basic radio system.
Let me summarize the most important properties of the E&M wave
It is a transverse wave of an oscillating E and B field. The E field and B
field are perpendicular to the direction of motion of the wave.
The E and B fields are perpendicular to one another
The E and B fields are in phase (they max out at the same time).
The amplitude of E and B are related by E=cB
The speed of the E&M wave in vacuum is
c=\frac{1}{\sqrt{\epsilon_0\mu_0}} = 299,792,458\;m/s \approx 3\times 10^8 m/s
Poynting Vector
The Poynting vector
\vec{S}= \frac{1}{\mu_0}\vec{E}\times{B}
encodes the amount of energy per area in the wave and also tells us the
direction of propagation.
Remember that in a transverse wave, there is no material that is moving in
the direction of the wave. The thing that is propagating is disturbance in
the electromagnetic fields. That disturbance does not have a physical,
touch, nature but it exists and it carries energy and momentum.