Of course, in an exam you might not always get told to find n, but instead be given i , n and asked to find r, so it is useful to have seen other vers...
LASERs make almost anything better, and that includes refracting light in physics lessons. Here's a guide to refracting LASER light, and some calculations you might need to do afterwards.
Step 1: Just a bit on theory
As a beam of light enters an optically more dense medium it slows down. If a beam of light is traveling diagonally, some parts will slow down before others. This causes the light ray to bend towards the normal (the normal is a line drawn perpendicular to the surface where the beam of light hits). The opposite happens when a light ray leave a more dense medium.