Why the ray of light passing through the centre of curvature of a concave mirror behave as normal while it doesn’t behave as normal when it passes through other points on the principal axis?

Remember that a concave mirror forms part of a hollow sphere.

Any line joining the centre of the sphere (the centre of curvature of the mirror) and any point on the mirror will be normal to the reflecting surface of the mirror.

Therefore A ray of light passing through the principal axis will be normal to the surface as it is passing through the centre of curvature of the mirror.

• The principal axis of a mirror is the straight line passing through the centre of curvature and pole