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 564 nm reflected at an angle of 29.1° relative to the normal. Find the number of ridges per mm on the CD. (Take m = 1.)

Answer 1