Plane Wave Front
The continuous locus of points having the same phase of vibration in a medium through which a wave propagates is called a wave front. Plane wave front is produced by extended sources like when we see a point object which produces a spherical wave front but far away when rays become parallel it produces plane wave front. As the distance from the source at light increases, the curvature of the wave fronts continues to decrease. Wave fronts coming tram a source at long distance will be plane. For this reason, the wave fronts coming from the sun or stars are considered to be plane. In fig (a), AB and CD are plane wave front. That means, if the locus of the particles in a wave is plane, then the wave front is called plane wave front. Waves having plane wave fronts are called plane waves.
Fig: Plane Wave Front
The simplest form of a wave front is the plane wave, where the rays are parallel to one another. The light from this type of wave is referred to as collimated light. It is a set of waves traveling in a plane. This is seen in lights coming from an infinite source.