Diffraction by an Edge

Waves passing an edge are diffracted.

Discussion

When waves are partially blocked by an obstacle or barrier, the part of the wave that is not blocked bends around behind the obstacle. This effect is called diffraction, the edge of the barrier acts as a point source, generating circular waves in the region near the edge. In contrast, if a beam of particles is partially blocked by a barrier, that part of the beam that is not blocked experiences no change in direction. Diffraction is, with interference, a key characteristic that distinguishes waves from particles.

The extent of diffraction is dependent on the frequency of the wave, being greatest at low frequencies and essentially vanishing at high frequencies. This effect of frequency on the extent of diffraction is best seen by comparing images from the beginning and middle of the movie with those near the end.