User's Manual

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Model No. OS-8170A Brewster’s Angle Accessory
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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,
n
1
sin
1
= n
2
sin
2
(1)
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*
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