1. The problem statement, all variables and given/known data S solid uniform glass sphere is surrounded by air. The sphere has radius R and refractive index n. As shown in the picture, a light ray travelling in air, parallel to a diameter of the sphere, enters the sphere, reflects off the far side, then exits the sphere travelling in a direction exactly opposite to its original direction. Showing all details of your solution, find the relationship that expresses x (for 0<x<R) in terms of n and R in the situation shown in the picture. 2. Relevant equations Snell's Law, nasin(thetaa) = nbsin(thetab) 3. The attempt at a solution I labelled the angle of incidence and angle of refraction as a and b in the diagram. Since n for air is one, the equation should become sin(a) = nbsin(b) Due to geometry, sin(a) will be equal to x/R. However, I cannot figure out an expression for sin(b) in terms of x, R, and n. I have tried for a long time, and just cannot figure out the geometry of the problem. Thanks for your help.