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December, 1926
AMERICAN CINEMATOGRAPHER
Twenty-three
(.Continued from Pate 11)
Laws of Reflection
THE law ruling the regular reflection of light is as follows:
"The angle that the incident ray makes with the normal to the reflecting surface at the point of incidence, is equal to the angle that the reflected ray makes with the same normal ; and the incident and the reflected rays are coplanar."
For short, let us say that the angle of reflection is equal to the angle of incidence and both rays are lying on the same plane.
This being true, we can easily trace geometrically the path of an incident and its corresponding reflected rays.
.-"V
A B Equals Reflecting Surface.
L Equals Luminous Point.
L O Equals Inicident Ray.
O N Equals Normal to A B at Point O.
O R Equals Reflected Ray
L' Equals Virtual Image of Point L.
a Equals Angle of Incidence.
a Equals Angle of Reflection.
a Equals a'.
Let A B (Fig. 2) be the section of the reflecting surface of an opaque body, a mirror for instance, and let the plane of the paper be the plane in which lies the incident ray L O, emanated by the luminous point L, and let O be the point at which the incident ray falls upon the surface.
Let O N be the normal to A B at the point O, that is to say, the line perpendicular to A B atO.
The reflected ray will follow a path O R, forming with O N, an angle NOR. equal to the angle L O N.
For the sake of simplicity, let us call the angle L O N by the letter a (alpha) and let the angle N O R be called a ' . simply, a equals a ' .
We will then have : angle of incidence equals angle of reflection; or L O N equals N O R, or simply, a equals a .
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