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Name: Tony K.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 2001-2002


Question:
I was studying on polarization of light and came across Brewster's angle. Even after much research on the Internet, I cannot find out WHY polarization occurs parallel to the surface along this angle. Why does it work? What is happening that my eyes cannot see?


Replies:
Tony,

Brewster's angle is the angle at which reflected light is perpendicular to refracted light (the light that continues on into the material). The effect of pure polarization at Brewster's angle was discovered by experiment: no theories predicted it. There are some theories regarding it, but nobody knows for sure why it happens. The most popular theory is as follows:

The electric charges in the glass (or other transparent material) oscillate perpendicular to the direction of the light waves within the material. Thus, they oscillate perpendicular to the refracted light. Because light waves are "side-to-side" oscillations (lateral waves), there must be some side-to-side motion in the charges producing the waves. When the reflected light is perpendicular to the refracted light, there is no oscillation in the reflection plane. Waves oscillating in the plane of reflection cannot be emitted as reflected light.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


The answer is simple in principle, but a bit more complicated in the details. The reflection and refraction of light by a surface is not simply the "bouncing off" of the incident beam from the surface. Rather, the oscillating electric vector of the incident beam causes the electrons in the reflecting/refracting medium to oscillate. These oscillations in turn produce the reflected/refracted beams. In the "particle" description of light replace the "oscillation of the electrons of the medium" to "elastic scattering of the photons by the electrons in the medium". That is the simple part.

The details are a bit more involved, but are explained far more concisely and lucidly than I would even attempt. See: Richard Feynman's "Lectures on Physics" Vol. I, Chapter 33, Sections 33-4 through 33-7.

Vince Calder



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