When light is emitted from a source, waves of
radiation travel in straight lines and in all directions.
Dropping a pebble into a pool of water can see a simple
example of motion, similar to that of radiation waves.
The waves spread out in expanding circles; similarly,
light waves spread out in all directions to form a sphere.
The boundary formed by each wave is called a wave
front. Lines, or rays, drawn from the light source to any
point on one of these waves indicate the direction in
which the wave fronts are moving. Light radiates from
its source in all directions until absorbed or diverted by
coming in contact with some substance or object.
The wavelength of a light wave is the distance from
the crest of one wave to the crest of the following wave.
Wavelength, frequency (the number of waves which
pass a given point in a unit of time), and speed are
related by the simple equation:
C = lF
C = speed
l = wavelength
F = frequency
Because the speed of electromagnetic energy is
constant, the frequency must increase if the wavelength
decreases and vice versa.
Wavelength is measured in angstrom units (A).
They may also be measured in millimicrons, or
millionths of millimeters (mA). Figures 5-7 and 5-8
show the visible and invisible spectrums colors in
relation to their wavelengths. Figure 5-8 shows that the
visible spectrum occupies only a small portion of the
complete electromagnetic spectrum extending between
4,000 and 7,000 angstroms only.
Figure 5-7.Wavelength of various visible and invisible
REFRACTION OF LIGHT BY A PRISM.
THE LONGEST RAYS ARE INFRARED; THE SHORTEST, ULTRAVIOLET.
WAVELENGTHS IN MILLIMICRONS
Figure 5-8.Wavelengths and refraction.