On the Discussion
Question page, the figure of the ball bouncing contained an angle θi.
This angle, called the angle
of incidence, describes how the ball approaches the surface.
This angle is measured from the path of the ball to the normal
to the surface rather than being measured from the path to the surface
itself. The diagram below illustrates why angles are measured in
|The figures to the left illustrate a (red) light beam
striking a surface that is not perfectly smooth.
Determining the normal to a rough surface can be difficult, as the normal will have a different orientation at each point on the surface. To construct a normal for such a surface, you must first draw a line tangent to the surface at the point where the light strikes the surface, then draw the normal which will be perpendicular to that tangent. Although sometimes tricky, the task will yield a normal from which consistent measurements of angles can be made.
The angle of incidence is not the only angle so defined.
The reflected light will make an angle
of reflection that is measured from the reflected beam to the normal,
and light that is not reflected but continues into the second material
will make an angle
of refraction with respect to the normal. These angles will
be discussed later in this lesson.
from the surface? Go to the next page to find out!
Copyright © 1999-2004 Doris Jeanne Wagner and Rensselaer Polytechnic Institute. All Rights Reserved.