The following animation illustrates the patterns of constructive and destructive interference that are produced by two point sources of equal power, rhythmically expanding and contracting in phase and with the same frequency. The two point sources are located exactly one wavelength apart.

Find out what happens in the following pages when the separation distance is further increased for a fixed frequency or when one varies the frequency of one of the sources for a fixed separation distance. The following configurations have been considered:

• Two wavelengths apart same frequency

• Two wavelengths apart  different frequencies

• Four wavelengths apart same frequency