# Reflection of light

There is a geometric way to show that the angle of incidence equals
the angle of reflection. If a person at
*A* looks in the mirror, she "sees" *B**, the image of
*B* in the mirror. Since light travels in straight lines (to
minimize travel time), the person at *A* thinks that
light travels straight to *B**. In order for its light to
have that appearance it must be reflected at an angle *a*
as shown in Figure 2.

### Figure 2: A geometric interpretation of reflection.

This technique of using mirror images is an example of the principle of
superposition. It is used frequently in physics to analyze the
behavior of electric fields.

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Frederick J. Wicklin <fjw@geom.umn.edu>
Paul Edelman <edelman@math.umn.edu>
Last modified: Tue Oct 24 15:00:25 1995