If sunlight shines straight onto a peacock feather, the feather appears blue whe

Question

If sunlight shines straight onto a peacock feather, the feather appears blue when viewed from 15 degree on either side of the incident beam of sunlight. The blue color is due to diffraction from the melanin bands in the feather barbules. Blue light with a wavelength of 468 nm is diffracted at 15 degree by these bands (this is the first-order diffraction) while other wavelengths in the sunlight are diffracted at different angles. What is the spacing of the melanin bands in the feather ? mu m A diffraction grating produces a first-order maximum at an angle of 19.2 degree. What is the angle of the second-order maximum?

Explanation / Answer

lambda = 468 nm

theta = 25 deg

d sin theta = m lambda

d = m lambda / sin theta

= (1 * 468 * 10-9) / sin 25

= 1.11 * 10-6 m

= 1.11 mum

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