If sunlight shines straight onto a peacock feather, the feather appears bright b

Question

If sunlight shines straight onto a peacock feather, the feather appears bright blue when viewed from 15 degree on either side of the incident beam of sunlight. The blue color is due diffraction from the melanin bands in the feather barbules, as was shown in the photograph on page 549. Blue light with a wavelength of 470 nm is diffracted at 15 degree by these bands (this is the first order detraction) while other wavelengths in the sunlight are diffracted at different angles. What is the spacing of the melanin bands in the feather

Explanation / Answer

Given: wavelength () = 470 nm; angle () = 150

Here the condition of diffraction is just like Brag's law

So considering the spacing to be 'd' we have the equation for first order diffraction

2*d*sin = or d = 470/(2*sin15) = 908 nm

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