Question

6) An astronomer using a fluorite refractor lens (n=1.434) wishes to observe the hydrogen alpha emissions from a nebula. These emissions have a wavelength of 656.3am. To maximize transmission of the light through the lens, a special optical coating having an index of refraction Or 1.355 is put on the front surface of the lens. What minimum thickness of such a coating would maximize the transmission of the light (in other words, it minimizes reflection)? 8) Two plane mirrors are arranged as shown below. A beam of light strikes the first one at an angle of 20' with respect to the horizontal. At what angle with respect to the horizontal does it leave the second mirror? 200

Answer 1

1)

Thickness of coating, d = lambda/4 sqrt(n1 n2)

d = (653.6 x 10^-9)/4 sqrt(1.355 x 1.434)

d = 1.18 x 10^-7 m

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