Chapter 19, Problem 56A

To determine

To describe:The demonstration one can do with CD and two laser pointers (red and green) along with the result to settle the disagreement between two persons.

Explanation of Solution

Introduction:

Diffraction grating is an optical element that comprises of a surface which is ruled with an equidistant, closely spaced and parallel lines. The lines in the grating are opaque and the spacing between the lines serves as a number of closely placed slits. CD’s can be used as a grating device because tracks of the CD acts as a grating. They can disperse the light beam passing through it and produce a spectrum of light by the principle of diffraction. The diffraction from the grating is governed by the light wavelength and also by the gaps between the lines in the grating.

One can shine the two laser pointers through a CD on to a nearby screen and can get a diffraction pattern on the screen. The color whose wavelength is longer will produce a pattern with more spacing between the dots than that produced by the smaller wavelength color. Because spacing between the dots in the diffraction pattern is directly proportional to the wavelength of light. Person M is right, red light has longer wavelength than green light.