wave front

wave front, imaginary surface representing corresponding points of a wave that vibrate in unison. When identical waves having a common origin travel through a homogeneous medium, the corresponding crests and troughs at any instant are in phase; i.e., they have completed identical fractions of their cyclic motion, and any surface drawn through all the points of the same phase will constitute a wave front.

The Figure shows a spherical wave front (w_s) for a sound wave spreading out from a point source and a plane wave front (w_p) for a parallel beam of light, such as that emitted from a laser. Wave fronts for longitudinal and transverse waves may be surfaces of any configuration depending on the source, the medium, and the obstructions encountered. See also Huygens’ principle.