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Pigments don't survive fossilization; even though we have fossil skin from dinosaurs, we don't know what color they were. But fossilization does preserve structure. Specimens from a rare cache of 50-million-year-old beetle fossils still show the microscopic layers that produced structural colors in the living creatures, and we can deduce the colors from an understanding of thin-film interference. One fossil showed 80 nm plates of fossilized chitin (modern samples have index of refraction n = 1.56) embedded in fossilized tissue (for which we can assume n = 1.33).

What is the longest wavelength for which there is constructive interference for reflections from opposite sides of the chitin layers?

Answer :

Answer:

Explanation:

Light gets reflected by a medium of higher  refractive index and then from a medium of lower refractive index a second time  so there will  be an additional phase difference of 180⁰.

For constructive interference in thin films  the condition is as follows .

2μd = (2n+1) λ/2

where μ is 1.56 , d is 80 nm λ is wave length of ligh and n is an integer .

For longest wavelength , n = 0

λ = 4μd

= 4 x 1.56 x 80 nm

= 499.2  nm .

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