PASCO OS-8170A Brewster’s Angle Accessory - Manual (Page 12)

Brewster’s Angle Accessory Model No. OS-8170A
12
®®
3. Remove the Analyzing Polarizer from the
Spectrophotometer Arm. Turn the Lens Mount so that the
index mark on the high step is at 85° on the Pivot Plate
(measured from the zero mark closest to the Beam
Splitter).
4. Rotate the Spectrophotometer Arm to about 85° (as
shown on the Digits display of the Angle), and, while watching the Digits display of the
Reflected Light Intensity, adjust the angle of the arm so that the laser beam reflected by the
“D” Lens shines on the #5 slit on the Aperture Bracket. (The angle does not have to be exact
- just close enough that you get enough light.)
5. If the maximum light intensity drops below 50%, adjust the round Polarizer nearest the laser
to increase the light intensity above 50%. Do not allow the reference intensity to exceed 95%.
(This will make the measurement as precise as possible. Since you are plotting the ratio of
polarized intensity over total intensity, changing the total intensity will not affect the ratio. As
you proceed it will eventually be impossible to make the maximum intensity above 50%.)
6. Place the square Analyzing Polarizer with its axis horizontal just in front of the Aperture
Bracket on the Spectrophotometer Arm. (Note: The Analyzing Polarizer must sit flat on the
arm.)
7. Press “Keep” to record the Angle, the Reflected Light Intensity, and the Reference Light
Intensity.
See “Entering the Data” (next page)
It is helpful to enter data in the table as it is collected so you can see the progression of data
towards the minimum.
When the polarizer is horizontal, the light passing through the polarizer is polarized
perpendicular to the surface of the D Lens. This is the polarized light that is a minimum at
Brewster’s Angle.
8. Rotate the square Analyzing Polarizer so its axis is vertical and set it on the
Spectrophotometer Arm just in front of the Aperture Bracket.
9. Press “Keep” to record the Angle, the Reflected Light Intensity, and the Reference Light
Intensity.
When the polarizer is vertical, the light passing through the polarizer is polarized parallel to the
surface of the D Lens. This is the polarized light that is a maximum at Brewster’s Angle. Both the
horizontal and vertical components are measured so the perpendicularly polarized light can be
normalized by dividing by the sum of the two components.
10. Remove the Analyzing Polarizer and set up for the next angle. Rotate the Lens Mount so the
index mark lines up with 80°, and move the Spectrophotometer Arm so that the angle in the
zero
mark
85°
Lens
Mount
Pivot
Plate