The law ofreflectiongoverns the reflection of light-rays off smooth conducting surfaces, such aspolished metalor metal-coated glass mirrors.
Consider a light-ray incident on a plane mirror, as shown in Fig.56. The law of reflection states that the incident ray, the reflected ray, and the normal to the surface of the mirror all lie in thesame plane. Furthermore, the angle of reflection
isequalto the angle of incidence
. Both angles are measured with respect to the normal to the mirror.
Figure 56:The law of reflection
The law of reflection also holds for non-plane mirrors, provided that the normal at any point on the mirror is understood to be the outward pointing normal to the local tangent plane of the mirror at that point. Forrough surfaces, the law of reflection remains valid. It predicts that rays incident at slightly different points on the surface are reflected in completely different directions, because the normal to a rough surface varies in direction very strongly frompoint to pointon the surface. This type of reflection is calleddiffuse reflection, and is what enables us to see non-shiny objects.
