http://www.ck12.org Chapter 13. Light
The energy of an electromagnetic wave travels in a straight line along the path of the wave. The moving light wave
has associated with it an oscillating electric field and an oscillating magnetic field. Scientists often represent the
electromagnetic wave with the image below.
The black line represents the straight path of the light itself. Along this path, there exists an electric field that will
reach a maximum positive charge, slowly collapse to zero charge, and then expand to a maximum negative charge.
Similarly, there is an changing magnetic field that oscillates from maximum north pole field to maximum south pole
field. Along the path of the electromagnetic wave, these changing fields repeat, oscillating over and over again.
However, the oscillating electric and magnetic fields demonstrate a weaving pattern that is not the way light travels.
For an electromagnetic wave, the crests and troughs represent the oscillating fields, not the path of the light.
Although light waves look different from waves in a rope, we still characterize light waves by their wavelength,
frequency, and velocity. We can measure along the path of the wave the distance the wave travels between one crest
and the succeeding crest, which is the wavelength of the electromagnetic radiation. Like transverse waves through a
medium, the frequency of electromagnetic waves is the number of full cycles of waves that pass a certain point in a
set unit of time. The velocity for all electromagnetic waves traveling through a vacuum is the same: 3. 00 × 108 m/s,
which is symbolized by the lower casec. The relationship, then, for the velocity, wavelength, and frequency of
electromagnetic waves is:c=λf.
The entirespectrumof electromagnetic waves includes very low energy electric waves up to very high energy
gamma rays. As you probably know, ultraviolet rays, X-rays, and radio waves are also waves on the electromagnetic
spectrum. The full electromagnetic spectrum is shown below. You can see that visible light is a very small fraction
of the electromagnetic spectrum.