In both cases, the process begins with an incident ray that strikes the surface - or enters the new medium - at a certain angle. This angle is called the angle of incidence, the angle between the incident ray and the normal line. The normal is just an imaginary line that's perpendicular to the surface. If this was a reflective surface, then we'd see a reflected ray bouncing off the surface with its own angle of reflection. The incoming angle is called *
