# Physics 312, Extra Credit for Week #5: due Apr 15, 1998, at 7 PM

Measure the index of refraction of a substance.

This project may be done by teams of 1-2 individuals. The goal is to measure the index of refraction of some material.

There are several ways you might proceed. In all cases, you may assume that the index of refraction of air is exactly 1, even though it's really a teeny bit larger.

• If you could find a prism, for example, you might measure the angle through which blue and red light are bent. You may use wavelengths of 400 nm for the bluest light in a visible spectrum, and 750 nm for the reddest light in a visible spectrum. The difference in these angles, plus a careful measurement of the size and shape of the prism, will yield the index of refraction of the prism material.

• You may also try to send a light beam through an interface between two materials -- for example, by shining a laser beam from air into water. If you can measure the angle of incidence at the interface, and the angle of refraction beyond the interface, then you can calculate the change in index of refraction between the two materials.

There may be other methods to measure index of refraction, too. You may adopt any method you wish, as long as you describe clearly how your method works.

If necessary, you can borrow a laser from the stockroom, or from me.

Once you've made the measurements and calculated the index of refraction in a substance, try to look up the accepted value for that substance. There are a number of values in your book; if you can't find an entry for your material, talk to me, and I'll try to help with some additional references. If there is a large difference (more than 10 percent) between your value and the accepted one, try to explain it.

Submit a report which contains a description of your method, with a clear drawing and all relevant dimensions. Include the data for your experiment, and all calculations. You may also include interesting items you discovered during the course of the procedure.