THE ELECTROMAGNETIC SPECTRUM
In previous chapters, we have seen that if we oscillate one end of a long rope, we
generate a wave that travels down the rope and has the same frequency as that of
the oscillation.
You can think of an electromagnetic wave in a similar way: An oscillating electric
charge generates an electromagnetic (EM) wave, which is composed of oscillating
electric and magnetic fields. These fields oscillate with the same frequency at
which the electric charge that created the wave oscillated. The fields oscillate in
phase with each other, perpendicular to each other and the direction of propagation.
For this reason, electromagnetic waves are transverse waves. The direction in
which the wave’s electric field oscillates is called the direction of polarization of
the wave. Most EM waves have electric fields oscillating equally in all
perpendicular directions to propagation and thus are unpolarized.
Unlike waves on a rope or sound waves, electromagnetic waves do not require a
material medium to propagate; they can travel through empty space (vacuum). When
an EM wave travels through a vacuum, its speed is constant.