1. The problem statement, all variables and given/known data 2. Relevant equations Snell's Law sin tetha1/v1 = sin tetha2/v2 n1 = c/v1 n1 . sin tetha 1 = n2 . sin tetha 2 3. The attempt at a solution I try to make triangle out of line PO, so that it will have correlation to tetha, since o = center, then let's say there's point C at circle circumference. then POC is isosceles triangle. PC^2 = PO^2 + CO^2 - 2PO.CO.cos tetha PC^2 = 2R^2 - 2R^2 cos tetha PC^2 = 2R^2 ( 1 - cos tetha) n value for air = 1.00 ? but I cannot find the correlation tetha to n, and especially h...?