This is a Java applet which demonstrates reflection, refraction, and Snell's Law. You can change the indices of refraction for the two media: n1 and n2 , and the angle of incidence theta1. The Reflectance R, and Transmittance T, indicate what fraction of the incident (blue) average energy density per unit time is reflected (green) and transmitted (red) respectively. R + T = 1.

Original applet