We describe the index of refraction of a material for sound waves to be the ratio of the speed of sound in air to the speed of sound in the material. Snell's law then applies to the refraction of sound waves. The speed of a sound wave is 1320m/s in water and 344m/s in air.
1. What is the critical angle for a sound wave incident on the surface between water and air?
2. Use your results to describe why it is possible to hear people on the opposite shore of a river or small lake extremely clearly.