PHY1033C
Fall 2011
Lab#3
How does Light Refract?
Safety First! The laser used in this experiment is “safe”, but DO NOT shine its light into your or
anyone else’s eye.
Goal: To measure the refraction of light when it passes from air to Plexiglass and back to air.
Part A: One interface that bends light
Materials: Laser Light Box, Plexiglass semi-circle, Protractor
Procedure: Setup the equipment as shown in the sketch on the following sheet. Use the single laser
setting on the light box so it produces one narrow beam of light. Position the light box so that the light is
directed along the normal line toward point O. Place the Plexiglass semi-circle on the lab sheet over its
outline with the flat surface facing the light box. Mark the line the light makes when it exits the
Plexiglass along the normal (the light should pass straight through the slab of plastic with no change in
direction). While being careful not to move the Plexiglass semi-circle, line up the laser along the AO line.
Using a sharp pencil, mark the position of the line of light as it comes out of the opposite side of the
Plexiglass. Adjust the laser light box so that it lines up with each of the other lines (BO, CO, DO and EO)
and mark the position of the line of light for each ray as it exits the Plexiglass semi-circle. Using the
straight side of the protractor, draw long lines connecting point O with each of your marks for the 5 light
rays and also extend the original AO, BO, CO, DO and EO lines further out on their side of the drawing to
make measurement easier. Align the protractor with the normal line and Point O and measure the
angles for each light ray as they enter (incident angle = ſi ) and exit (refracted = ſr ) the semi-circle.
Enter the incident (incoming) and refracted (exiting) angles in a table in your lab book that looks just like
the table listed below.
Ray
AO
BO
CO
DO
EO
Angle ſi
Angle ſr
Sin ſi
Sin ſr
Sin ſi/Sin ſr
Questions to be answered in lab book:
1) Where does the bending of the light ray take place?
2) What is the average index of refraction that you calculated?
3) Use the data above to write a general statement about the refraction of light as it moves from air
into plastic.
4) Write a general statement about the ratio of Sin ſi /Sin ſr .
Staple the next page into your lab book in the appropriate place.
O
Part B: How is light refracted through a thick lens?
Materials: Laser Light Box, Plexiglass lens, Protractor
Procedure: Predict the path that the light rays shown in the diagram will take as they travel
through the lens and exit the lens by drawing on the paper. Use a dashed line for your
prediction. Drawing a normal line at the point where the light enters and exits the lens may be
helpful.
Using a five-lase setting on the light box, shine rays parallel to the “light ray direction” line. Use
a solid line to show the light ray path as it moves to the right side of the paper.
Questions to be answered in lab book:
1. How well do your guesses line up with the result? What and why are there differences,
if any?
2. What special feature in the lens system can you now identify?
Staple the paper into your lab book in the appropriate place