1. The problem statement, all variables and given/known data A glass block 3cm thick and of index of refraction 1.5 is placed on a luminous point. Find the smallest diameter of an opaque object which will prevent any light from passing out of the top of the block. 2. Relevant equations Snell's Law 3. The attempt at a solution My main problem is not understanding the question. The question had no diagram attached. I assume there is no distance between the luminous point and glass block. This makes calculations difficult? However, I have checked the back of the book and there is a single correct answer.