Saturday, 24 April 2010

Brewster’s law

Around 1812 Brewster discovered that for different glasses the p-polarized ray (in the plane of the paper) vanished completely at a particular angle of incidence i. Furthermore, by rotating the analyzing calcite crystal through 90°, the s-polarized ray (directed out of the plane of the paper) became extinguished. He then discovered that the refracted ray angle r was simply related to the incident ray angle i by
equation_1
Brewster's_Law
Snell’s law of refraction between the two media is
equation_2
where n1 and n2 are the refractive indices of the media, respectively. For air n1 = 1 and for glass n2 = n. Substituting the first equation into Snell’s law leads to
equation_3
This equation is known as Brewster’s law. Its immediate practical use was that it enabled the refractive index of glass to be determined by reflection rather than by refraction; the measurement of the refractive angle r by transmission is difficult. The result of this discovery was that it led to the rapid development and measurement of new optical glasses.

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