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Reflection
The behaviour of light is easy to predict. A light that reflects off a surface obeys the law of reflection. The law of reflection is a law that dictates the angles a light reflects off. The diagram below illustrates the law of reflection:
In the diagram, the ray labelled R is the reflected ray. The grey dashed line N is the normal, which can be drawn perpendicular to the surface. The normal line divides the angle between the incidence ray and the reflected ray. The angle between the incidence ray and the normal is called the angle of incidence ( labelled i ). The angle between the reflected ray and the normal is called the angle of reflection ( labelled r ).
Most importantly, the normal divides the angle equally. So the angle of incidence is equal to the angle of reflection.
Angle of Incidence = Angle of Reflection