Sierzega/Ferri: Optics 5
Observation Experiments: Light Bending
Go to:
http://phet.colorado.edu/en/simulation
/bending-light
You have a laser beam (press the
button to turn it on!) that is shining
from air into some other material
such as water, glass, mystery material
A, or mystery material B. Use water
for part 1 of this lab.
5.1. Observational Experiments (Air  Water)
Grab the protractor from the toolbox and set it up so that you can easily measure the angle at which the laser
beam strikes the water (relative to the normal line) and the angle that it makes with the normal line once it is in
the water.
a. What happens to the laser beam as it enters the water?
b. In “Laser View” - click on “wave”. Pose an explanation that explains why the light bends when it enters the
water.
Buggé: Optics 6
c. Collect the following data to help you find the relationship between the incident ray (the incoming laser beam
from the air) and the refracted ray (the laser beam after it is bent by the water). Measure your angles relative to
the normal.
Angle of Incident
Ray, Θ1
Angle of Refracted
Ray, Θ2
20 °
40 °
60 °
80 °
90 °
d. Does the reflected beam behave in the same way it would if it were reflected off another smooth surface, like
a mirror?
e. When the incident ray enters the water and bends, does it bend toward the normal line or away from the
normal line?
5.2 Observational Experiments (Water  Air)
a. What happens to the laser beam as it enters the air?
b. In “Laser View” - click on “wave”. Pose an explanation that explains why the light bends when it enters the
air.
Sierzega/Ferri: Optics 5
c. Collect the following data to help you find the relationship between the incident ray (the incoming laser beam
from the water) and the refracted ray (the laser beam after it is bent by the air). Measure your angles relative to
the normal.
Angle of Incident
Ray, Θ1
Angle of Refracted
Ray, Θ2
20 °
40 °
60 °
80 °
90 °
d. Does the reflected beam behave in the same way it would if it were reflected off another smooth surface, like
a mirror?
e. When the incident ray enters the air and bends, does it bend toward the normal line or away from the normal
line?
5.3 Summarize
a. Can you see a pattern in the way a ray of light bends when it passes across a boundary surface between two
substances?
b. What determines how much the ray bends when it crosses a boundary surface?
Buggé: Optics 6
5.4. Summarize your conclusions - refraction of light rays
Review your observations in the previous exercise. Consider the examples pictured below.
air
glass
air
air ethyl
alcohol
water
1. What are the dotted lines in the figure above?
2. Record the way light bends when passing from air into each material and from each material back into the air. Describe the
direction of refraction in terms of the normal to the surface at the point where the ray passes through (toward the normal or away from
the normal).
Materials
Direction of refraction: from air
Direction of refraction: to air
From air into water:
From water into air:
From air into glass:
From glass into air:
From air into alcohol:
From alcohol into air:
Water and air
Glass and air
Alcohol and air
3. Describe any patterns that can be detected in all the experiments above
Relative amount of refraction
Sierzega/Ferri: Optics 5
5.5 Predict and test - triangular prism
1. Use the pattern you found in the previous exercise to predict what will happen when a beam of light passes through a triangular
prism.
incident light ray
air
glass
2. Perform the experiment. Did the results match your prediction?
5.6. Represent and reason - sunken toy
Mike has dropped his new Samsung Galaxy IV smartphone into the swimming pool at south.
1. Draw the ray of light that reaches Mike's eye from the beautiful widescreen display.
2. What is the apparent position of this wonderful device from Mike's point of view?
air
water
Buggé: Optics 6
5.7. Predict and test
We observed that when light passes from air into another material, its path refracts towards a normal line that is perpendicular to the
surface of the material. When light passes from another material into air, its path refracts away from the normal line.
Use this pattern to predict the path of light rays moving through a prism in each of the cases below.
1. Glass prism in air
air
glass
laser beam
2. Hollow glass prism in water. You can ignore the thin glass walls of the hollow prism.
laser beam
water
air
3. Solid glass prism in water
Note that the light bends toward the perpendicular line when going from water to glass, and vice versa in going from glass to water.
laser beam
water
glass