1. The problem statement, all variables and given/known data So anyway in the diagram of my book there is a ray hitting the centre in the flat part of a semi circular prism. The question in the book states "Ignoring partial reflection, we know that each ray will pass through the flat surface and then pass through the curved surface, Which of the rays refract only once? Explain" I also do not get why it refracts more than once if the light rays do not hit the centre. 2. Relevant equations Snell's law 3. The attempt at a solution I know from the centre to the edge it is the radius of the semi circular prism. When the light refracts from the centre onto the edge i know that the normal is perpendicular to that point and the angle of refraction = 0.