What is the longest wavelength λ of light that will exhibit constructive interference at normal incidence? the keratin layers are thin enough that you can think of them as representing the surfaces of a 200-nm "film" of air?

560nm

Explanation:

You can use the following expression for thin films:

where n is the index of refraction, d is the thicknes of the thin film and m is the order of the diffraction pattern. For keratin layers we can use n=1.40. For the longest wavelenth we use m =1.

Hence, we obtain:

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answer: i pick a

explanation:

elctricity and magnet is conversion to it