PASCO OS8170A User Manual
Instruction Manual
Brewster’s Angle
Accessory
Model No. OS-8170A
012-08489B
*012-08489*
Brewster’s Angle Accessory Model No. OS-8170A
®
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Table of Contents
Equipment.....................................................................................................3
Introduction...................................................................................................5
Theory...........................................................................................................5
Setup Instructions.........................................................................................6
Sensor Setup..............................................................................................10
Procedure...................................................................................................11
Analysis ......................................................................................................13
Questions....................................................................................................14
Teacher’s Guide: Discovering Brewster’s Angle.........................................15
Further Investigation...................................................................................20
I. Intensity of Reflected Light (without a polarizer)
II. Intensity of Transmitted Light
III. Snell’s Law
Acknowledgements..................................................................................... 22
Appendix A: Creating Equations in DataStudio.......................................... 23
Appendix B: Laser Safety Instructions........................................................ 24
Technical Support....................................................................................... 26
Copyright and Warranty Information........................................................... 26
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Model No. OS-8170A Brewster’s Angle Accessory
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Beam Splitter
Semi-circular Acrylic “D” Lens
Pivot Plate Assembly
Analyzing
Polarizer
Lens Holder
Polarizers
Lens Mount
Brewster’s Angle Accessory
Model No. OS-8170A
Equipment
Included Equipment Model Number
1. Polarizer Assembly (1 lens holder and 2 round polarizers) 003-09784
2. Analyzing Polarizer (1), Lens Mount (1), and Pivot Plate Assembly (1) 003-08332
3. Beam Splitter (1) OS-8171
4. Semi-circular Acrylic Lens (1) (“D” Lens) 003-08545
Additional Equipment Required - Option 1
Educational Spectrophotometer Accessory* OS-8537*
• Collimating Slits
• Spectrophotometer Base
High Sensitivity Light Sensor (2) PS-2176 or CI-6604
Rotary Motion Sensor (1) PS-2120 or CI-6538
Aperture Bracket (2) OS-8534A
Optics Bench, 60 cm (2) OS-8541
Basic Optics Diode Laser (1) OS-8525A
OR (see next page)
Model Number
*The Accessory includes unlisted items that are not used for the experiments.
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Brewster’s Angle Accessory Model No. OS-8170A
®
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Additional Equipment Required - Option 2
Educational Spectrophotometer System OS-8539
• Educational Spectrophotometer Accessory OS-8537
• Optics Bench, 60 cm
• High Sensitivity Light Sensor
• Rotary Motion Sensor
• Aperture Bracket OS-8534A
Basic Optics Diode Laser OS-8525A
Optics Bench, 60 cm OS-8541
High Sensitivity Light Sensor CI-6604
Aperture Bracket OS-8534A
PLUS
Patch Co rd (2) See PASCO web site* or catalog
PASCO computer interface See PASCO web site* or catalog
PASCO data acquisition software See PASCO web site* or catalog
Suggested Additional Equipment
Model Number
OS-8541
CI-6604
CI-6538
Green Diode Laser OS-8458
*www.pasco.com
Complete packages of all the equipment and sensors are available from PASCO. Choose the EX9919A Brewster’s Angle Experiment (ScienceWorkshop) if you want to use ScienceWorkshop
sensors or choose the EX-9965A Brewster’s Angle Experiment (PASPORT) if you want to use
PASPORT sensors.
PASCO's Brewster's Angle Accessory is designed to be used with the Educational
Spectrophotometer System (OS-8539). In addition to the Educational Spectrophotometer
System, the experiments need the Basic Optics Diode Laser (OS-8525A), and one or more of
each of the following: Optics Bench (OS-8541), Aperture Bracket (OS-8534A), and High
Sensitivity Light Sensor. A PASCO computer interface, and PASCO data acquisition software
are also required for the experiments.
NOTE: A folder for the Brewster’s Angle experiment is available as a “.ZIP” file to download
from the PASCO web site. Go to the page that shows the EX-9919A or EX-9965A Brewster’s
Angle Experiment and click “Download”. The folder contains DataStudio setup files and sample
data files for ScienceWorkshop and PASPORT sensors, and Microsoft Word “.DOC” files for
the experiment procedure.
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Model No. OS-8170A Brewster’s Angle Accessory
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Figure 1: Brewster’s Angle Accessory Setup for Experiments
High Sensitivity Light Sensor
Aperture Bracket
Analyzing Polarizer*
“D” Lens* on Lens Mount*
Spectrophotometer Degree Plate
Rotary Motion
Sensor
Beam
Splitter*
Lens Holder* with Polarizers*
Collimating
Slits
Diode
Laser
Optics Bench
Aperture
Bracket
High
Sensitivity
Light Sensor
Interface
*Items included in the Brewster’s Angle Accessory
Pivot Plate Assembly*
Introduction
The Brewster’s Angle Accessory (OS-8170A) is used in optics for studying the polarization of
reflected light and for determining Brewster’s angle. The accessory consists of a lens holder with
two polarizers, a rotating platform (Pivot Plate Assembly) with a semi-circular “D” lens, an
analyzing polarizer, and a beam splitter.
When light reflects off a nonconducting material, the reflected light is partially polarized. The
amount of polarization depends on the incident angle and the index of refraction of the reflecting
material. The incident angle that gives the maximum polarization is called Brewster's angle.
Light from a Diode Laser is reflected off the flat side of an acrylic semi-circular (“D”) lens. The
reflected light passes through an analyzing polarizer and is detected by a Light Sensor. The angle
of incidence is measured by a Rotary Motion Sensor mounted on the Spectrophotometer Base.
The intensity of the reflected polarized light versus the incident angle is graphed to determine
the angle at which the light intensity is a minimum. This is Brewster's angle, which is used to
calculate the refraction index of acrylic.
Theory
When unpolarized light reflects off a nonconducting surface, it is partially polarized parallel to
the plane of the reflective surface. There is a specific angle called Brewster's angle at which the
light is 100% polarized. This occurs when the reflected ray and the refracted ray are 90 degrees
apart.
According to Snell's Law,
n1sin
= n2sin
1
2
(1)
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Brewster’s Angle Accessory Model No. OS-8170A
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Figure 2: Polarization of Unpolarized light
n
2
n
1
------
P
tan=
Spectrophotometer
Base
Spectrophotometer
Degree Plate
Spectrophotometer
Arm
Line up the 180
degree mark
Index
line
Figure 3: Assemble the Spectrophotometer Base,
Degree Plate, and Arm
where n is the index of refraction
of the medium and is the angle of
the ray from the normal.
When the angle of the incident ray
is equal to Brewster's angle, p,
n1sinP = n2sin
2
(2)
and since P + 2 = 90o,
= 90o- P, and
2
= sin(90o- P) =
sin
2
sin90ocosP - cos90osinP =
cos
P
Substituting for sin2 in Equation (2) gives n1sin
P = n2
cos
P
Therefore, (3)
Setup Instructions
Assemble the Spectrophotometer Base
1. Attach the Spectrophotometer Base at
one end of an Optics Bench.
2. Attach the Spectrophotometer Degree
Plate to the Base, but align the Degree
Plate “backwards”; that is, line up the
180 degree mark on the Degree Plate
with the index line on the Base.
3. Attach the Spectrophotometer Arm to
the Degree Plate.
(For instructions on setting up the
Spectrophotometer parts, see the
Educational Spectrophotometer
Manual. You can download a PDF file
of the manual from the PASCO web
site. Go to the page that shows the
OS-8539 and click the “Manual” tab.)
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Model No. OS-8170A Brewster’s Angle Accessory
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Figure 4: Mount the Rotary
Motion Sensor to the Base
Rotary Motion
Sensor
Hinge
Spindle
Degree Plate
4. Mount a High Sensitivity Light Sensor to an Aperture
Bracket and attach the Aperture Bracket/Light Sensor to
the Spectrophotometer Arm.)
5. Mount the Rotary Motion Sensor to the upper holes on the
hinge of the Spectrophotometer Base. Mount the Spindle
on the shaft of the Rotary Motion Sensor so that the bigger
diameter of the spindle is against the edge of the
Spectrophotometer Degree Plate (see Figure 4).
6. Connect a patch cord from an electrical ground to a bare
piece of metal on the Spectrophotometer Base, as
instructed by your teacher.
Attach the Pivot Plate and Lens Mount
1. Screw the Pivot Plate into the threaded hole in the center of the Spectrophotometer Degree
Plate.
2. Screw a wing nut onto the threaded post of the Pivot Plate that extends below the
Spectrophotometer Base.
3. Turn the Pivot Plate so that the index mark at the edge of the plate above the “N” in the word
ANGLE is aligned with the zero degree mark on the Spectrophotometer Degree Plate.
Note: Make sure that the Pivot Plate is not screwed down too tightly against the Degree Plate.
The Spectrophotometer Arm should be able to rotate freely and the Pivot Plate should remain
stationary as the Spectrophotometer Arm is moved. (Screw the Pivot Plate almost all the way
down and then tighten the wing nut under the Spectrophometer Base.)
4. Place the Lens Mount on the Pivot Plate so that the hole in the bottom of the lens mount
matches the post on the pivot plate.
5. The Lens Mount has two vertical index marks. For reflected light, use the mark that is on the
side with the higher step. Line up the index mark with the zero degree angle on the edge of
the Pivot Plate that is closest to the laser.
(Note: The other mark can be used for transmission studies in a Snell’s Law experiment.)
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Brewster’s Angle Accessory Model No. OS-8170A
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Figure 5: Laser and
Collimating Slits on bench
Laser
Collimating
Slits
Figure 6: Mount the Beam Splitter
Beam Splitter
2nd Optics
Bench
Align the Laser Beam
1. Put a Laser Diode on the end of the bench opposite to the
Spectrophotometer Base.. Connect the laser’s power supply to a
grounded electrical outlet and plug the power cord into the laser .
Turn on the laser (the ON-OFF switch is on the back of the
laser).
WARNING: Do not look directly into the beam of the
laser light source or reflected light from the laser light source, such
as from a mirror. Although the laser used in this experiment is of
low power, looking directly into the laser light source or its
reflected light from a mirror could cause eye damage. T o avoid eye
injury, do not look directly into the laser beam and wear laser
protective goggles. For more information about laser safety, see
Appendix B of this manual.
2. Set the Spectrophotometer Arm so that 180 degrees on the
Degree Plate is next to the index mark. Set the Aperture Bracket
disk to slit #5. Use the x-y adjustment knobs on the back of the
laser to aim the laser beam at the center of Aperture Bracket slit
#5.
3. Place the Collimating Slits on the optics bench and adjust the slit position on the Collimating
Slits so that the laser beam passes through slit #5 and also still shines on slit #5 on the
Aperture Bracket disk (see Figure 5).
4. Adjust the Brewster’s Lens Mount so that the index line on the higher step of the Lens Mount
is aligned with the zero mark on the Pivot Plate.
5. Place the “D” Lens on the lower step of the
Lens Mount with the flat side of the lens
against the edge of the higher step. If the laser
beam is not still centered on slit #5 of the
Aperture Bracket, adjust the “D” Lens side-toside until the laser beam shines on slit #5.
Make sure the “D” Lens is firmly against the
step.t
6. Mount he Beam Splitter on the bench near the
center of the bench. Check that the transmitted
laser beam still illuminates the #5 slit on the
Aperture Bracket on the Spectrophotometer
Arm. If necessary, loosen the adjustment screws on the Beam Splitter holder and move the
holder to align the laser beam with slit #5 on the Aperture Bracket disk.
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