Snell's Law I
This interactive animation allows you to explore Snell's law by shining a laser from air into a different medium, which can be either water or glass. Move the laser to change the angle of incidence, and observe how the refracted beam changes direction accordingly. The angle of incidence and the angle of refraction are marked theta i and theta r, respectively. Note that these angles are always measured relative to the normal, i.e. to the line perpendicular to the refracting surface. Make sure you observe carefully in which direction the beam is refracted when it propagates from the medium with the smaller index of refraction to the optically denser medium, i.e., the one with the larger n.