The surface of a compact disk (CD) behaves as a kind of diffraction grating. Whe

Question

The surface of a compact disk (CD) behaves as a kind of diffraction grating. When light is reflected from the surface, each of the closely spaced ridges on a CD behaves as the source of a spherical light wave. Except for the fact that light is reflected rather than transmitted, the effect is the same as for the transmission gratings described in the text; that is, one sees a spectrum of colors (see figure below). Suppose a beam of sunlight is normally incident on a CD. You see yellow light of wavelength 599 nm reflected at an angle of 31.8° relative to the normal. Find the number of ridges per mm on the CD. (Take m = 1.)

Explanation / Answer

d sin theta = lambda
d sin31.8 = 599x10^6 mm (lambda converted to mm)
solve for d, it will be in mm/ridge

d = 1.136x10^9
so invert it
1/d = 0.88x10^-9___ridges/mm

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