Template:POTD/2009-09-23

Picture of the day

Wavefronts from a point source in the context of Snell's law, which describes the relationship between the angles of incidence and refraction, when referring to light or other waves, passing through a boundary between two different isotropic media, such as water and glass. The region below the gray line has a higher index of refraction and proportionally lower wave velocity than the region above it. The dotted red line is perpendicular to the wavefronts and thus represents a Fermat-shortest path from the source to a point in the lower medium.Image credit: Oleg Alexandrov