using Snell's Law (sin(theta1)/sin(theta2) = v1/v2 where (theta1) is the angle of incidence and (theta2) is the angle of refration. The number V1/V2 is called the index of refraction. The index of refraction from air to water is 4/3. If a ray of light passes through the surface of a lake at an angle of incidence of 70 degrees what is the angle of refraction?