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Oijl

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## Homework Statement

A glass lens is coated on one side with a thin film of magnesium floride (MgF2) to reduce reflection from the lens surface. The index of refraction of MgF2 is 1.38; that of the glass is 1.50. Assume that the light is perpendicular to the lens surface and that the thickness of the coating is the least possible needed to eliminate the reflections of light of wavelength 550 nm at normal incidence.

(a) Calculate the percentage by which reflection is diminished by the coating at 445 nm.

(b) Calculate this percentage for a wavelength of 695 nm.

## Homework Equations

maxima: 2L=(my)/n

minima: 2L=((m+0.5)y)/2

[y is lambda)

## The Attempt at a Solution

What is meant (mathematically) by a diminished reflection?

This is an extension of a sample problem in my textbook; in the book, the problem is to find the thickness of MgF2 that'll minimize reflection (99.6nm). But the only equations I can think of relating to this system use the quantities: thickness of MgF2, n-air, n-MgF2, n-glass, wavelength, and integer m. It doesn't seem, to me, that any of these are what I should be comparing in the 99.6nm thickness and 445nm thickness situations in order to find the percentage by which reflection is diminished.