The previous page stated that the angle of incidence always equals the angle of reflection. This law applies whether the item reflecting is a ball on a tennis court, a ground ball bouncing along a baseball field, or light reflecting from a mirror or a wall. It is a universal law. Yet common experience tells us that a baseball sometimes takes an unexpected bounce straight up, and that a laser beam striking a classroom wall must be reflecting into a wide range of angles since the spot on the wall can be seen by the entire class. This apparent contradiction is resolved once we understand the difference between total reflection and diffuse reflection.
Consider a beam of laser light striking a surface as shown in the figures to the left. Each region of the beam is traveling in the same direction when the beam strikes the surface.
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The fielder who missed the ground ball was not necessarily ignorant of the law of reflection. Instead, the ball could have struck a rough region of the field. The law of reflection still held, but the normal to the surface was not necessarily vertical. Since the fielder's expectations were based on a horizontal surface, the direction the ball traveled was a surprise. (Note: this is not the only explanation for a fielder's error, but it is a possible explanation.)
Diffuse and total reflection, and their difference, are
also crucial to the operation of CD-ROMs. The module
on optical storage addresses this dependence in more detail.
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Move on to the next part of the module to find out! |
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Copyright © 1999-2004 Doris Jeanne Wagner and Rensselaer Polytechnic Institute. All Rights Reserved.