PHYS 1400: Physical Science
Laboratory Manual
POLARIZATION
INTRODUCTION
Chances are you know more about polarized light than you think
you do. You may own a pair of Polaroid sunglasses, and if you do
you know how well they cut the reflected glare (off the water, for
example, if you spend time on a boat, or off the road if you spend a
lot of time driving). Well, the same technology which makes your
polarized sunglass lenses effective is also used for 3D movies.
You have probably seen several 3D movies recently, and you
probably haven’t had to wear those odd-looking red-blue lenses.
When you saw “Avatar” or the latest “Pirates of the Carribean,” the
3D glasses looked pretty much like a pair of gray-lensed
sunglasses. And they pretty much were.
The difference between your sunglasses and the 3D glasses has to
do with the orientation of the polarizing filters covering the lenses.
Your sunglasses will have both lenses oriented the same way, to
reduce glare off of horizontal surfaces. Each lens of the 3D
glasses will have the polaroid filter oriented differently,
Top: Old-fashioned anaglyphic 3d glasses
perpendicular to each other. What this means is that the light
Bottom: New-fangled polarized 3d glasses
which passes through one lens will be blocked by the other. What
makes the movie appear 3D is the fact that it was shot with two
cameras, separated by a small distance (like your two eyes). The signal from the first camera is polarized to be
perpendicular to the signal from the second, so when the movies is played with both tracks simultaneously, one eye
sees one signal, and the other eye sees the other, slightly different signal. Your brain interprets these separate signals
and puts together one complete 3D image for you.
OBJECTIVES
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EQUIPMENT
Observe the difference between a polarized and an unpolarized light source
Measure the amount of transmitted light through a polarizing filter
Establish a relationship between the filter orientation and amount of light
transmitted for a pair of polaroid filters
Prepare light curves for a single filter and a pair of polaroid filters
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LabQuest unit
Light sensor
Optics bench
Light source
Polaroid filters
PROCEDURE
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Use the loose polaroid filters to examine the
overhead fluorescent light sources. Look at
the light through the filter, then rotate the
filter. Notice if there are any changes in the
amount of light transmitted through the filter.
An unpolarized light source will not show
noticeable changes, regardless of the
orientation of the filter.
Look for some reflected glare (off the floor
tiles, or possibly the whiteboard). Again,
examine what happens as you view the
reflected glare through the filter. If the light
source is polarized, it will dim noticeably for
certain orientations of the filter as it is rotated.
Place the light source on the optics bench.
Snap each of the two circular polarizers to a
separate component stand.
Clamp the light sensor to the vertical rod, and
align it with the light source, using one of the
Use the Parallel Ray Lens on the front of the light source to narrow the
polarizers as a guide. The sensor switch
light beam down
should be set to the 0-600 lux scale.
Connect the light sensor to the LabQuest and
switch the LabQuest on. Under the Sensor menu of the Meter tab, choose the Data Collection option. Select
Events with Entry as the data collection mode. The Number of Columns should be 1. Give it the name Angle, with
units of deg (or degrees). Tap OK to continue.
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PHYS 1400: Physical Science
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Laboratory Manual
Position one polaroid filter directly in front of the light sensor. Turn the filter so that 0° lines up with the notch on
the component stand. Now adjust the position of the light source so that the illumination is 200 lux. You do not
need to record the distance, and the illumination will not be perfectly equal to 200; just get it as close as you can.
Once the light source is in position, do not move it.
To begin data collection, tap the GO button. You should notice a small KEEP icon appear directly next to it. To
record data, tap the KEEP icon. When you are asked for the event name, type in 0 (for the angle of the filter) and
tap OK. Data collection resumes, and you can adjust the filter angle to 10°. Keep the new illumination data, type
in 10 for the event name. Continue to rotate the filter by 10° increments and record the illumination data, until you
have completely turned the filter through 360°. Rotate only the filter; do not adjust the position of the light source.
End data collection by tapping the STOP button, then make sure to save the trial by tapping the File Cabinet icon.
Repeat the experiment with two filters between the source and the sensor. With both filters aligned at 0° and
placed on the bench, reposition the light source so that the illumination is again 200 lux. Again, the distances do
not need to be recorded, just place the light source close enough to register 200 lux.
Leave one filter always at 0°, and do not rotate it. Collect data as you rotate the second filter only. Rotate the filter
in 10° increments as before, until you have again turned the filter through a complete 360°. STOP collecting data,
and save the run by tapping the File Cabinet icon.
DATA & ANALYSIS
You do not need to transcribe the entire data set into your notebook, but you should record the following illuminations:
ANGLE
(°)
ONE FILTER
ILLUMINATION
ANGLE
(LUX)
(°)
ILLUMINATION
(LUX)
ANGLE
(°)
TWO FILTERS
ILLUMINATION
ANGLE
(LUX)
(°)
0
230
0
230
50
270
50
270
90
320
90
320
140
360
140
360
180
ILLUMINATION
(LUX)
180
1. Display both graphs of Illumination as a function of Angle on the LabQuest simultaneously. Tap Graph Options
under the Graph menu of the Graph tab. Click the checkboxes for the Graph 1 Y-Axis to display both Run 1
Illumination and Run2 Illumination. Make a sketch of this graph in your notebook.
2. Why is there such a big difference between the plots? If both trials began with a 200 lux illumination, why does one
curve (which one is it?) dip down so much more dramatically than the other? What difference does adding a
second filter make?
3. When you used two filters, what is the angle between the filters for maximum light transmission? How are they
oriented when transmitted light is minimum?
4. When you used the loose filters to examine the fluorescent lighting and the reflected glare, what did you notice?
Which of your data curves would correspond to viewing the light, and which curve
would correspond to the glare?
5. The figure on the right shows how a pair of
polarized 3D glasses separates the signals
from the screen. Explain why you could not
use a regular pair of polarized sunglasses
to view a 3D movie.
6. The figure on the left shows a pair of
polarized lens glasses held in front of a
computer screen. Are these 3d glasses?
How do you know?
7. I have a pair of polarized sunglasses. I also
have a glossy screen on my computer.
Polarized 3d movie glasses
When I sit in front of my computer and put
on the glasses, I cannot see anything on
the screen. It looks completely dark. However, when I tilt my head 90° right
or left, the screen becomes clearly illuminated. Explain this!
Are these 3d glasses?
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