1. The problem statement, all variables and given/known data So we have recently done a reflection and refraction lab measuring both the angles of reflection, refraction as the angle of incidence was changed from 30-80. The last question on my lab report asks why the piece of plastic used must be semi-circular in nature. It also asks us to produce a diagram. However, I am unsure of exactly why it must be semi-circular. 3. The attempt at a solution My first though is that it has to have the same distance from the "entry point" of the light into the plastic medium to the "exit point" of the light. Therefore, for every angle the light passes through nearly the exact same amount of material. However, I am unsure if this is true.