Figure H10.1: A diagram to show a ray of light travelling through air as a medium impinges upon a reflective surface such as glass and is reflected from it.
Consider a ray of light in air that comes into contact with (impinges upon) a flat surface of a different medium, such as glass, for example. Three things may happen:
1. All the light enters the medium;
2. Some of the light enters the medium;
3. None of the light enters the medium.
Reflection occurs when some or all of the light does not enter the medium. This will be the case in both 2 and 3 above. The law of physics that governs reflection is a simple one summarised thus:
The angle of incidence is equal to the angle of reflection.This is simple because it never varies and applies in all instances of reflection.