- William C. Evans
This applet shows an incident light ray and the resulting refracted (transmitted) and reflected rays, using Snell's Law. The relative intensities of the reflected and transmitted rays are indicated by the lengths of the respective vectors, which are calculated using Equations 2.58, 2.59 on page 44 of Introduction to Modern Optics 2nd Ed., G.R. Fowles, Dover, ISBN 0-486-65957-7. This material is also in Optics, 2nd Ed., E. Hecht, Chapter 4, ISBN 0-201-11609-X. The dotted line in the lower right quadrant shows the critical refraction angle, which is not exceeded regardless of the incidence angle. Using a larger refractive index for the top section (n1) than the bottom section (n2) can show total internal reflection. (The light source is fixed in the top section.) The maximum incidence angle is deliberately restricted to a bit less than 90 degrees. Note that both angles are measured w.r.t. the normal to the boundary between the media; this normal is vertical in the drawing.