Seeing Snell's Law: Developing Visual
Demonstrations for the Teaching of Optics

Jennifer Nierer, John Noé, and Harold Metcalf

Laser Teaching Center, Department of Physics and Astronomy

It is human nature to have a curiosity for the way the universe works. An effective way of investigating many laws in physics is through recreating situations or circumstances where they occur naturally. Analytical investigations to discover the causes and reactions of our universe is the principle that all research labs are based upon. Optics is demonstrated almost everywhere because anything that deals with light is demonstrating a principle of optics. Through different surfaces and different substances light will behave differently. It doesn't take an extensive knowledge of optics to notice this. A good scientific eye will result in many observations and open opportunities for many inexpensive studies using even simple household products.

This experiment began in a short research class in the WISE program (WSE187) where I had the opportunity to satisfy a personal curiosity about the bending (refraction) and reflection of light. The experiments were done in a small fish tank filled with layers of solutions containing different concentrations of household corn syrup. A green laser beam of 532 nm, which is the best wavelength to be seen by the eye, creates stunning effects by scattering from small particles added to the solution. The laser shone into the tank bends (refracts) at the division of two different solutions because each has a different index of refraction. The amount of bend is determined by Snell's law, a basic physics principle. As time progresses the solutions in the fish tank diffuse causing a gradual change in the indices of refraction. In the beginning the bends made by the laser beam have relatively sharp angles, but these become smoother and more continuous over time. Also, with the use of corn syrup mixtures in the tank, bacterial growths develop that scatter the laser beam in different ways that also evolve with time. This is a simple experiment in which many different phenomena can be studied. All of the results were recorded through photographs taken with a digital camera.

Future plans for this research are to develop more optics demonstrations exposing sophisticated physics with simple inexpensive materials.