The Ripple tank provides a dramatic demonstration of the general properties of waves and propagation phenomena.
1) Reflection and refraction. By using the linear dipper bar plane parallel waves can be produced. Reflection and refraction of waves can be demonstrated by using appropriate barriers in the water tank.
2) Interference occurs when two point source dippers generate circular waves. The distance between the sources and their frequency can be regulated.
3) The famous double slit experiment: When a plane wave encounters a barrier with two holes, these act like two point source dippers, giving rise to the same interference pattern.
4) The transparent lens cross section is covered by only a shallow layer of water. This decreases the propagation velocity corresponding to an increased index of refraction.