1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution glass is more dense than air, so the ray will go towards the normal. I know that when it meets the normal, it totally internally reflects, (after looking at the answer), but how do you know? TIR only happens when a ray is going from a medium with higher refractive index to a medium with a lower refractive index, but that does not mean it is necessarily going to happen. I know what the critical angle is, but not the incident angle, so I can't tell if the incident angle is > the critical angle, in which case TIR would happen.