1. The problem statement, all variables and given/known data A beam of light is emitted 8.0 cm below the surface of an unknown liquid. The light beam is angled in a way that it strikes the surface 7.0 cm from the point directly above the light source. The light beam is totally internally reflected. What is the index of refraction of the unknown liquid? 2. Relevant equations n1sinΘ1° = n2sinΘ2° n = c/velocity in medium 3. The attempt at a solution tanΘ = 7/8 Θ = 41.8° Attempt 1: n1sin41.2° = n1sin41.2° Cancels out... Attempt 2: n1sinΘ° = 1sin90° Two variables! Attempt 3: n1sin41.2° = 1sin90° n1 = 1.518166 n1 = 1.5 Could do this, although I don't even know whether it is correct, since it does not use the actual critical angle.