Refraction
If a sheet of glass is placed in the tank, the depth of water in the tank will be shallower over the glass than elsewhere. The speed of a wave in water depends on the depth, so the ripples slow down as they pass over the glass. This causes the wavelength to decrease. If the junction between the deep and shallow water is at an angle to the wavefront, the waves will refract. In the diagram above, the waves can be seen to bend towards the normal. The normal is shown as a dotted line. The dashed line is the direction that the waves would travel if they had not met the angled piece of glass.
In practice, showing refraction with a ripple tank is quite tricky to do.
- The sheet of glass needs to be quite thick, with the water over it as shallow as possible. This maximizes the depth difference and so causes a greater velocity difference and therefore greater angle.
- If the water is too shallow, viscous drag effects cause the ripples to disappear very quickly.
- The glass should have smooth edges to minimise reflections at the edge.
Read more about this topic: Ripple Tank