Attachment # 3
The law of reflection
Objectives:
At the end of the activity, the student should be able to verify and understand the Law of
Reflection.
Materials:
• Laser pointer, glass rod cylinder, flat mirror, paper protractor on last page
• Support for mirror (clamps,) paper, pen or pencil, 12” ruler with cm tickmarks
Procedure and Observations
1. Describe the direction you think a single beam of light will reflect from the surface of a
mirror:
2. Make a prediction - will the angle that the beam of light reflects from the surface of the mirror
be smaller, larger, or the same as the angle of the original beam to the surface of the mirror?
3.On the last page of this experiment sheet there is a picture of a protractor – use that page and
place the page on a table. Place a flat mirror on the straight-line part of the protractor. Set-up
your Laser pointer and glass cylinder so that the Laser projects a vertical line that hits the mirror
at the center point of the protractor. Project this line at a 45-degree angle to the flat surface of
the mirror as measured on your protractor
4. Note that depending on the thickness of the glass of your mirror, reflections may not come just
from the front of the mirror and that other reflections of the Laser light may be seen. Observe
this closely. How might you explain this effect?
5. Make 2 dots along each projected Laser light line then using a ruler, trace along the projected
Laser light line to mark the incident and reflected rays onto the protractor paper (resulting in the
picture below when the Laser is turned off). Remove the mirror from the paper then extend the
ray lines to the mirror line.
6. Measure the angle of incidence θi and angle of reflection θr from the perpendicular (0º) line on
your protractor paper. Write down your results in the table below.’
7. Do all of the above again with the Laser pointed at the mirror using 20 and 60 degrees – fill in
your results in the table below.
Case #
Measured angle of
incidence
Measured angle of
reflection
8. Explain any relationship you have found between the 2 measured angles (was your prediction
above is correct?)
9. Describe where the incident ray, reflected ray and normal line lie. This is the second law of
reflection.
Generalization: