Brewster's angle
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Brewster's angle (also known as Polarization angle) is an optical phenomenon first discovered by the Scottish Physicist, Sir David Brewster (1781-1868).
When light moves between two media of differing refractive index, light which is p-polarised with respect to the interface will not be reflected from the interface at one particular incident angle, known as Brewster's angle.
It may be calculated by:
- <math>\theta_B = \arctan \left( \frac{n_2}{n_1} \right) <math>,
where n1 and n2 are the refractive indices of the two media.
Note that, since all p-polarised light is refracted, any light reflected from the interface at this angle must be s-polarised. A glass plate placed at Brewster's angle in a light beam can thus be used as a polariser.
For a randomly polarized ray incident at Brewster's angle, the reflected and refracted rays are at 90° with respect to one another.
For a glass medium (n2≈1.5) in air (n1≈1), Brewster's angle for visible light is approximately 56° to the normal. The refractive index for a given medium changes depending on the wavelength of light, but typically does not vary much. The difference in the refractive index between ultra violet (≈100nm) and infra red (≈1000nm) in glass, for example, is ≈0.01.
See also: