TC 9-64 _________________________________________________________________________
1-82. One theory after another attracted the approval and acceptance of
physicists. Today, some scientific phenomena can be explained only by the
wave theory and others only by the particle theory. Physicists, constantly
searching for some new discovery that would bring these two theories into
agreement, gradually have come to accept a theory that combines the
principles of the two theories.
1-83. According to the view now generally accepted, light is a form of
electromagnetic radiation; that is, light and similar forms of radiation are
made up of moving electric and magnetic fields. These two fields are
explained thoroughly later in this chapter.
1-84. James Clark Maxwell, a brilliant Scottish scientist of the mid-
nineteenth century, constructed an oscillating electrical circuit, which he
used to show that electromagnetic waves could move through empty space.
Light eventually was proved to be electromagnetic.
1-85. Current light theory says that light is made up of very small packets of
electromagnetic energy called photons (the smallest unit of radiant energy).
These photons move at a constant speed in the medium through which they
travel. Photons move at a faster speed through a vacuum than they do in the
atmosphere, and at a slower speed through water than air.
1-86. The electromagnetic energy of light is a form of electromagnetic
radiation. Light and similar forms of radiation are made up of moving electric
and magnetic forces and move as waves. Electromagnetic waves move in a
manner similar to the waves produced by the pebble dropped in the pool of
water discussed earlier in this chapter. The transverse waves of light from a
light source spread out in expanding circles much like the waves in the pool.
However, the waves in the pool are very slow and clumsy in comparison with
light, which travels approximately 186,000 miles per second.
1-87. Light radiates from its source in all directions until absorbed or
diverted by some substance (figure 1-17). The lines drawn from the light
source (a light bulb in the example in figure 1-17) to any point on one of these
waves indicate the direction in which the waves are moving. These lines,
called radii of the spheres, are formed by the waves and are called light rays.
Although single rays of light do not exist, light "rays" are used in illustrations
as a convenient method to show the direction in which light is traveling at
any point.
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