Explorations in Refraction

Science Teachers Day -- Mar. 30, 2002

This web site is http://www-unix.oit.umass.edu/~phys125/ScienceTeachers/

Subject Description
Technical Details
Related Fun Stuff


Prof. Guy Blaylock


Lederle Grad Research Tower Rm 1034


(413) 545-0993


Subject Description

The material presented in these lectures derives from an introductory course on light and vision for non-scientists, which I have taught for several years. This course covers a wide range of subjects including basic optics, photography, light in nature, visual anatomy, visual perception, and many topics in modern technology.

For Science Teacher Days I have selected a few topics on the subject of refraction. In this discussion we will explore the connection between the speed of light and the bending of light in transparent materials, leading to Snellıs law of refraction. I will offer an elegant explanation for this process in terms of Fermatıs principle of least time. We will also study the closely related topics of total internal reflection (the principle behind light fibers) and dispersion (the principle behind the prism). Finally, we will take a photographic tour through a variety of atmospheric optical phenomena, including the green flash, rainbows, sun dogs, halos and mirages.

Along the way I will try to tease your imagination with a few puzzles:
Why does a beer mug appear to have more liquid in it than it really does?
Why does a diver see light only from a narrow cone above?
How did Erik the Red see Greenland from hundreds of miles away, around the curve of the earth?
... and a few other questions.

A complete syllabus is available below.

Technical Details

Other Related Websites

In its simplest incarnation, the telescope is merely a pair of lenses or a mirror and a lens for viewing distant objects. However, modern day research telescopes can be far more sophisticated and the results far more impressive than what Galileo first used to view the moons of Jupiter. The image at the left is the deep field view from the "Hubble space telescope". Only a few dots of light in that photo are stars, the rest are galaxies. Clicking on the image will take you to a larger version suitable for viewing. The following "link" takes you to an enlargment of a portion of the deep field showing one of the most distant galaxies observed by man (arrow).
For a basic introduction to refraction, Rick Reed has produced a nice web page on the subject. Follow that up with a tour of the Hyperphysics web page on total internal reflection to round out your education.
The physics of rainbows was first correctly explained in a treatise by Rene Descartes in 1637. In that treatise he carefully traced light rays through a spherical drop of water to determine how the different colors are dispersed. The linked image at the left will take you to a site with a Java demo of ray tracing through a spherical waterdrop. There you can adjust the incident light rays to understand how different rays behave and how they contribute to the pattern of light that emerges.
Note: If you are interested in further study about light in nature, you may wish to check out Robert Greenler's book from the bibliography, or Tom Arny's astronomy 105 course on weather. Prof. Arny's course covers some of the topics we discuss in our classroom, including halos, mirages, and glories.
The "green flash" is one of the most elusive of atmospheric optical phenomena. It is visible on rare occasions shortly after sunset or before sunrise, when a small green flash appears in the sky above the sun. There are a number of online resources describing this phenomenon. Andrew T. Young has put together some of the most detailed web pages, including links to a large variety of images, careful explanations of mirages and atmospheric dispersion, and simulations like the one at the left. The linked image will take you to his main page.
Les Cowley has put together an impressive collection of atmospheric optics images (including rainbows, glories and ice halos) and provided brief explanations for each. The linked image at left will take you to his main web page.

Last updated March 25, 2002