Lesson 1 - Light Reflection
Light Reflection simulates the Law of Reflection and explores the relationship
between the angle of incidence and the angle of reflection.
Prerequisites
Students should have a basic understanding of
rectilinear propagation and the geometry of a triangle.
Learning Outcomes
Students will be able to define the Law of Reflection and create correctly-labeled
ray diagrams that include multiple reflectors.
Instructions
Students should understand the applet functions that are described in Help and ShowMe.
The applet should be open. The step-by-step instructions on this page are to
be done in the applet. You may need to toggle back and forth between instructions
and applet if your screen space is limited.
Contents
- The Law of Reflection
- Multiple Mirror Reflections
- A Technological Application - The Corner Reflector
1. The Law of Reflection
The applet will be used to demonstrate the Law of Reflection. On the applet,
select 
mode and click "Data"
(
). The applet
will create a display similar to that shown in Figure 1. Take note of
the labels and definitions that will not appear on the applet display.
Figure 1
| normal |
a straight line drawn perpendicular to the mirror surface at the point
of reflection |
| incident ray |
incoming ray |
| reflected ray |
outgoing ray |
| θin |
the angle between the incident ray and the normal line |
| θout |
the angle between the reflected ray and the normal line |
|
- The mirror angle can be adjusted by using the the angle slider
( ). The mirror position can be adjusted
by clicking and dragging the mirror on the screen.
Adjust the position and/or angle of the mirror. Record the values for θin and θout for
five different rays when the mirror is at various angles or positions. Record
your observations in Table 1.
|
θin |
θout |
_____ |
_____ |
_____ |
_____ |
_____ |
_____ |
_____ |
_____ |
_____ |
_____ |
|
- The Law of Reflection is one of the most basic of all laws in optics. It
relates the angle of incident to the angle of reflection. On the basis of the
investigation that you just performed, state the Law of Reflection in the box below.
|
2. Multiple Mirror Reflections
- Two mirrors are joined at a 120o angle, as shown on the diagram
below. An incident ray contacts the first mirror at an angle of 65o
to the normal. Calculate the angle A that the ray has with respect to
the normal of the second mirror. Carefully label all the angles on the
diagram and show your work in the space below. (Hint: remember that
the sum of the interior angles in a triangle is 65o.
|
- Challenge: Orient both mirrors so that multiple reflections
occur and that the final reflected ray is still traveling in its original
direction (see figure on the right). How must the mirrors be oriented
for this to happen?
|
3. A Technological Application - The Corner Reflector
- Orient the mirrors so that they meet at a right angle as
shown in the diagram on the right. Mirrors in this configuration form
what is called a corner reflector. Position the mirrors so that
a multiple reflection occurs (i.e. the ray hits both surfaces) but be
sure to maintain the 90 degree orientation between the mirrors. What
special property does the direction of the reflected ray have?
|
-
Corner reflectors are commonly used in reflective tape on clothing
and in road side reflectors. Explain why this technology is particularly
effective for night time visibility issues.
|
Physics 20-30 v1.0
©2004 Alberta Learning (www.learnalberta.ca)
Last Updated: June 16, 2004