Alabama Science in Motion
Light: Polarization with Light Sensor
Polarization with Light Sensor
Purpose
The purpose of this activity is to investigate how the intensity of light from a small light source
changes as it passes through a single polarizer, and how it changes when it passes through two
polarizers.
Qty Equipment and Materials
Qty Equipment and Materials
1
GLX
2
1
PASPORT Light Sensor PS-2106A 1
Optics Holder
1
PASPORT Extension Cable
1
Large Base and Support Rod
1
Basic Optics Light Source
1
Three Finger Clamp
Polarizers
Background
Normally, light is unpolarized. That means that the
light waves vibrate in all planes perpendicular to the
direction that the light wave travels.
A polarizer only allows light that is vibrating in a
particular plane to pass through it. This plane forms
the “axis” of polarization. For example, if the
polarizer is arranged in such a way that it only allows
the vertical plane of light to pass through it, then its
axis of polarization would be vertical (that is, at 0º to
the vertical).
If unpolarized light shines through an “ideal”
Fig. 1: Unpolarized and
polarizer, how much of the original light would be
polarized light
transmitted through the polarizer? An ideal polarizer
transmits half of the original light. Since in reality no polarizer is “ideal”, how much would be
transmitted?
The light that is transmitted through one polarizer is polarized in one plane. If this polarized light
shines upon a second polarizer, the axis of which is at an angle that it is perpendicular to the first
polarizer, no light would be transmitted through the second polarizer.
Prediction
1.
What would happen to the intensity of light when it passes through one polarizer?
2.
What would happen to the intensity of light when it passes through two polarizers that are
arranged at an angle of 0º to each other?
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Alabama Science in Motion
3.
Light: Polarization with Light Sensor
What would happen to the intensity of light when it passes through two polarizers that are
arranged at an angle of 90º to each other?
Preview
Use a PASPORT Light Sensor to measure the light intensity from a small light source when the
light travels through a single polarizer and then when it travels through two polarizers. Use the
Xplorer GLX to record and display the light intensity and the distance. Change the angle of one
polarizer relative to the other and compare the light intensity.
Safety Precaution

Follow all directions for using the equipment.
Procedure
GLX Setup
1.
Connect a PASPORT Extension Cable to the
PASPORT Light Sensor and plug the extension cable
into a sensor port on the top of the Xplorer GLX.
2.
Turn on the GLX.

The Graph Screen shows Light Intensity (lux) versus
Time (s). The file is set to measure light intensity 5
times per second (5 Hz).
3.
In the Home Screen (
), use the arrow keys to select
Digits and press
to activate your choice. The
Digits screen shows ‘Light Intensity (lux)’.
Fig. 1: Digits screen
Equipment Setup
1.
Set up the Basic Optics Light
Source on a table so the
point source aims
horizontallly.
2.
Mount the Light Sensor to a
support rod and adjust the
sensor so it is aligned with
the point source on the light
source. Put the sensor a few
centimeters from the point
source.
3.
Press the range selection
button on the Light Sensor
next to the icon of the sun
(
Fig. 2: Equipment setup
).
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Alabama Science in Motion
Light: Polarization with Light Sensor
Arranging the Polarizing Sheets
Two polarizers at 0º: The two polarizing filters are arranged so the axis of
transmission of the second filter is parallel to the axis of transmission of
the first filter. (The second polarizing filter does not change the light
intensity transmitted by the first polarizing sheet.)
Two polarizers at 45º: The second polarizing filter is arranged so its edge is
along the imaginary diagonal of the first polarizing filter.
Two polarizers at 90º: The second polarizing filter is turned 90º to the first
polarizing filter.
Record Data

NOTE: The procedure is easier if one person handles the polarizing
filters and a second person handles the Xplorer GLX.
1.
Connect the power cord to the Light Source to turn it on.
2.
From The GLX set up, the GLX should already be in Monitor mode
and the Digits Display automatically shows the current Light
Intensity in Lux. Do not press the record for this experiment.
3.
Write in your data table the value of the light intensity
with no polarizer.
4.
Put one polarizing filter between the light source and the
sensor.
5.
Record the value of the light intensity when the light
passes through one polarizer.
6.
Arrange two polarizing filters so the angle of the axes of
transmission is 0º.
Fig. 3: No polarizer
7.
Put the two polarizing filters between the light source
and the sensor and record the new value of the light intensity when the light passes through
two polarizers at 0º.
8.
Turn the second polarizing filter so it is at an angle of 45º to the first polarizing filter.
Record the new value of the light intensity.
9.
Finally, turn the second polarizing filter so it is at an angle of 90º to the first polarizing
filter. Record the new value of the light intensity.
10.
When you are finished collecting data, unplug the power cord from the Light Source and
turn off the GLX.
11.
Put away the equipment as directed by your teacher.
Analysis
Examine your recorded values of light intensity.
Use your results to answer the questions in the Lab Report section.
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Alabama Science in Motion
Light: Polarization with Light Sensor
Student Data Sheet
Name:
Partner’s Name (s):
Date: ___________
Period:
Prediction
1.
What would happen to the intensity of light when it passes through one polarizer?
2.
What would happen to the intensity of light when it passes through two polarizers that are
arranged at an angle of 0º to each other?
3.
What would happen to the intensity of light when it passes through two polarizers that are
arranged at an angle of 90º to each other?
Data Table
Arrangement
Light Intensity
No polarizer
One polarizer
Two polarizers at 0º
Two polarizers at 45º
Two polarizers at 90º
Questions
1.
How did the light intensity through one polarizer compare to the light intensity through no
polarizer?
2.
How did the light intensity with two polarizers at 45º compare to the light intensity with
two polarizers at 0º?
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Alabama Science in Motion
Light: Polarization with Light Sensor
3.
How did the light intensity with two polarizers at 90º compare to the light intensity with
two polarizers at 0º
4.
For two ideal polarizers, the light intensity when the polarizers are at 90º should be zero.
Why was the light intensity for the two polarizers at 90º not zero?
5.
Do your results support your prediction?
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