PASCO OS-8170A Brewster’s Angle Accessory - Manual (Page 11)

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Model No. OS-8170A Brewster’s Angle Accessory
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Note: If the Reflected Light Intensity is as high as possible without exceeding 95%, but the
Reference Light Intensity is above 95%, try one of the following to reduce the Reference Light
Intensity:
• Slightly adjust the second optics bench from side-to-side so that only part of the laser beam
enters through slit #5 of the Aperture Disk.
• Rotate the Aperture Disk in front of the second light sensor so that the laser beam enters slit
#4 instead of slit #5.
Zero the Rotary Motion Sensor
1. To zero the Rotary Motion Sensor, first remove the “D” Lens. Adjust the Spectrophotometer
Arm if needed so that the laser beam is centered on slit #5 on the Aperture Bracket disk. (The
180° mark on the Spectrophotometer Degree Plate should be near the index line.)
2. Click “Start” and slowly move the arm back and forth so that the slit moves through the width
of the laser beam. Stop at the position where the Digits display shows maximum intensity.
3. Click “Stop” and do not move the arm until you use the program to take the actual data run.
(This insures that the zero for the Rotary Motion Sensor is at the center of the laser beam.)
4. Replace the “D” Lens on the lens mount against the step, centering it so the laser beam still
shines on slit #5.
Note about angle measurement: The angle of reflection from the “D” Lens is calculated by
dividing the actual angle measured by the Rotary Motion Sensor by two. The best procedure is
to set the index line on the high side of the Lens Mount to a particular angle (such as 85°) and
then move the Spectrophotometer Arm so that the angle shown on the Digits display is the same
as the angle of the Lens Mount. Note that to get the laser beam exactly on the #5 slit in front of
the Light Sensor, you must make fine adjustments while watching the Digits display for the
maximum light intensity. You can adjust either the Lens Mount or the Spectrophotometer Arm
until the intensity is maximized.
Procedure
Taking Measurements
1. Lighting: Turn off the room lights when making a measurement. (A small light might be
useful for seeing the computer keyboard and for putting the Analyzing Polarizer on and off.)
2. Click “Start”. The “Start” button in the toolbar will change to “Keep” . Do
not click the red square (“Stop”) on the “Keep” button until all of the procedure steps are
completed.