Wave front is defined as the imaginary surface constructed by the locus of all points of a wave that have the same phase. This could be where all the crests are, where all the troughs are or any phase in between. Wave fronts are useful for showing how waves move in two dimensions. The length between two lines on a wave front is exactly one wavelength.

The direction of travel of the wave fronts is shown by a straight line with an arrow. It is called a ray. A ray is a line extending outward from the source and representing the direction of propagation of the wave at any point along it. Wave fronts and rays are always perpendicular to each other.

Key terms

• Wave front: A wave front is the set of all locations in a medium where the wave is at the same phase.
• Ray: Rays are lines that show the direction of propagation of a wave.