Question

All incident rays passing through the centre of curvature of a spherical mirror, retrace their path after reflection. Give reason.

Answer 1

1. The angle of incidence and the angle of reflection lie along the normal for a concave mirror.
2. This point of contact would meet at $90$ degrees where the radius of curvature is perpendicular to the tangent making the incident ray and the reflected ray coincide with each other.
3. The ray of light passes through the centre of curvature of a concave mirror it strikes the mirror along the normal ray, and it incidences onto the mirror at an angle of 90 degrees.
4. Hence, the incident ray coincides with the normal. Therefore, the angle of incidence $=0$
5. So, as we know according to the law of reflection, the angle of reflection $=0,$
6. Hence, the angle of reflection tends to zero degrees, thus the ray of light retraces its path.