1. The problem statement, all variables and given/known data I've preformed an experiment where in a ripple tank I had to count the number of waves and length of as long a train of waves as possible, so that I can calculate the wavelength. A stroboscopic light was used and I had to count the number of bright patches/shadows of the ripples cast at the bottom of the tank. There was a ruler submerged in the bottom of the tank to read the length. The question is, in what ways can refraction (bending of light) cause any errors in the readings? This is a photo of the situation: http://img405.imageshack.us/img405/3217/experimentlw.jpg 2. Relevant equations Snell's Law 3. The attempt at a solution I understand from Snell's law that when a beam of light enters a more optically dense medium with greater index of refraction (in this case water), it bends toward the normal. Can I use this to argue that the shadows/bright fringes of the waves have bended slightly and do not really correspond to the exact reading of the ruler at the bottom of the tank? If not, what else can I cite as a source of error due to refraction?