Dispersion measurements with minimum and maximum deviated beams

The prism spectrometer has been the standard apparatus for index of refraction measurements and a typical instrument in undergraduate laboratories for dispersion experiments. Because much care must be employed when aligning a prism spectrometer, a more robust method for measuring index of refraction is needed. By using a laser, prism, rotating platform, and tape measure, we can measure the index of refraction to five significant figures. Due to its ease of use, undergraduates can make more accurate measurements with this method than by using a poorly aligned prism spectrometer. Although a tunable laser is preferable for easily changing wavelengths, two laser pointers, one red and one green, may be used, allowing for an inexpensive method of accurately obtaining the constants in the two-term Cauchy equation relating the index of refraction to the wavelength. (c) 2006 American Association of Physics Teachers.