Editing Wave interference (section)

=== Between two spherical waves ===
[[File:wavepanel.png|thumb|Optical interference between two point sources that have different wavelengths and separations of sources.]]

A [[point source]] produces a spherical wave.  If the light from two point sources overlaps, the interference pattern maps out the way in which the phase difference between the two waves varies in space. This depends on the wavelength and on the separation of the point sources.  The figure to the right shows interference between two spherical waves.  The wavelength increases from top to bottom, and the distance between the sources increases from left to right.

When the plane of observation is far enough away, the fringe pattern will be a series of almost straight lines, since the waves will then be almost planar.