The Law of Reflection
Tennis players can generally predict which direction a
ball will go as it bounces off the court. We can also predict the
direction of a reflected light beam. Light reflects off a smooth
surface in the same manner that a ball reflects off a smooth tennis court.
This behavior is described by the law of reflection. The law
of reflection simply states that the angle of reflection (as measured to
the normal) always equals the angle of incidence (as measured to the normal):
This relationship is illustrated below.
|In the figure to the left, a laser beam traveling through
an optical fiber (shown in incredibly slow motion) reflects off the lower
edge of the fiber. The normal to that edge is indicated by the dashed line.
As the beam approaches the edge of the fiber, it makes an angle of incidence
with respect to the normal.
|The reflected beam travels off at an
angle of reflection
respect to the normal.
|The law of reflection says that this
angle of reflection will always equal the angle of incidence θi.
Why doesn't a shortstop
always correctly predict how the ground ball will bounce?
Does he not know the law of
reflection? Is the law not always valid?
Go to the next page to learn
when the law of reflection appears not to hold!
© 1999-2004 Doris Jeanne Wagner and Rensselaer Polytechnic Institute.
All Rights Reserved.