This java applet shows the physics behind a beam of light impinging at some angle

The java applet was divided into two region lower half (water) and upper half (air).

Click links to switch: between water-air and  air-water cases

Usage: You will find a flashlight under the water surface. (Picture)

Another similar applet can be found at [url=]Intensity of reflected s-wave/p-wave
Check out the following URL if you are interested in [url=]Guide To Choosing A Personal Flashlight[/url].