Display of colors by a CD can be understood in terms of the working of a plane optical reflection grating. The data which represents the music on the CD is in the form of very small pits arranged in a tightly wound spiral track in its silvery surface. The distance between two neighboring tracks is 1.6 micrometers which is only several times the wavelength of visible light. This small spacing is responsible for the wonderful colors reflected by a CD which works just as a diffraction grating. When light falls on a plane reflection grating, it is scattered in all directions by each of its reflecting stripes. These waves from individual gaps are termed wavelets. When we look at the grating from a distance, wavelets from different pits travel different distances to reach the retina of our eye, so we see different colors coming from the CD.
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