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# Brewster's Law

"If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans."
Stephen Hawking

- By applying the boundary conditions for electromagnetic waves striking the boundary between two media it can be shown that the intensity of the reflected and refracted waves depend on the polarisation of the incident wave.

- In particular, for unpolarised light incident on the boundary at a specific angle, θp , the reflected light contains only one polarisation. When this occurs the reflected and refracted light rays are at 900 to each other,

- Using Snell's law we can show that,

> This relationship is known as Brewster's Law.

- For light incident on water (from air) we find that θp= 530. Thus, at this angle the light reflected from the surface is (linearly) polarised. If this reflected wave is viewed with polarised sunglasses (which block this particular polarisation), no reflective glare is observed - allowing the observer to see clearly underwater.

"Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read."
Groucho Marx

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu