I use a ripple tank to show the properties of waves to my classes. Today Derwent Water was acting as a ripple tank. The waves were coming in towards me as I took the picture. The straight edged waves appearing in the picture would be called plane waves. They hit the smaller rocks close to the shore and that produced circular ripples that were reflections. Reflection should produce waves with the same wavelength but if you enlarge the photograph above, you'll see a disturbance in the water between the nearest rock and the National Trust Centenary memorial. There was a small rock coming in and out of the water. The circular ripples it produced had a smaller wavelength than the plane waves coming in. There can be two reasons for this. One is that there is a refraction effect and that the waves are slowing down in shallower water around the submerged rock. I saw no evidence of the plane waves bending though. The second reason would be that the rock was being hit at a higher frequency than the way the plane waves were formed. This might be the answer because of the way that the rock was sometimes submerged and sometimes out of the water.
The bigger rock in this picture was never submerged and seemed to produce circular ripples with a wavelength closer to that of the plane waves.
