Question

When will a ray of light falling on a curved surface retrace its path ? Pls answer fast and correct

Answer 1

Answer:

If light falls perpendicular to the surface of mirror, that is the angle of incidence is zero degrees then the angle of reflection is also zero. Hence

Answer 2

Answer:

For any curved surface , light rays may retrace their path back , only when they are Incident perpendicular to the mirror surface.

The reason is simple :

We know that Angle of Reflection is equal to Angle of incidence . So whenever a light ray falls perpendicular to its surface , it's angle of incidence is 0° , similarly angle of Reflection is also 0°.

Hence light travels it's path back.

A classic example of perpendicular retracing:

Whenever light ray passes through the Centre of Curvature of a concave mirror (curved surface) , it retraces it's path back because it is incident at an angle of 90° to the surface.