To reduce the reflection coefficient of light from optical glasses, a thin layer of a transparent substance is applied to their surface, whose refractive index n is less than that of glass. (The so-called “clarification method” of optics.) Determine the minimum thickness of the applied layer, assuming that the light rays fall perpendicularly on the optical glass. Explain why lenses with “coated optics” have a purple-violet (lilac) tint?

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