We define 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 can be applied to the refraction of sound waves. Speed of sound in water is 1320m/s. a) Which medium has the higher index of refraction for sound? b) What is the critical angle for a sound wave incident on the surface between air and water? c) For total internal reflection to occur, does the sound have to be traveling in air or water?