Reflection

2.6 Curved mirrors

Laws of reflection

The normal

For plane mirrors, the normal corresponds to the ray that reflects back on itself. Furthermore, this line bisects the angle of deviation. This description of the normal matches exactly the behaviour of the last of the three principle rays that we have just discussed. When a pencil of light is directed at the center of curvature of a mirror, it reflects back on itself.
It is now possible to generalize the concept of the normal for curved mirrors. The laws of reflection can now be generalized to apply to curved mirrors, in addition to plane mirrors.

Laws of reflection

The behaviour of light reflected by a curved mirror is subject to the same laws as that of plane mirrors.

• First Law:
  The incident ray, the reflected ray, and the normal all lie on the same plane
  
  .
• Second Law:
  The angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal.

Characteristics of the normal

The normal bisects the angle contained between the incident ray and the reflected ray. For a curved mirror, the normal is drawn at the point of incidence, perpendicular to the plane of the mirror.

Prediction of behaviour of any incident ray
Parabolic mirrors
Convex mirrors