Question

Figure shows a small concave mirror with \[CP\] as its principal axis. A ray $XY$ is inclined to the mirror. Which of the four rays can be the reflected ray?

A. $1$
B. $2$
C. $3$
D. $4$

Answer 1

Hint: We know every reflecting surface follows the laws of reflection whether it is a plane mirror or a spherical mirror. These are the laws of reflection: The angle of incidence is equal to the angle of reflection second, all three rays, incident, normal, and reflected, are in the same plane and the third one the incident and reflected rays are on opposite sides of the normal.

Complete step by step answer:
We know if a ray of light comes from infinity parallel to the principal axis, it always passes through the focus of the mirror. If a ray of light passes through the centre of curvature, the reflected ray always retraces its path through the centre of curvature. So, here the rays through the centre of curvature act as normal to a tangent plane at the mirror. Now, if we retrace the path for the reflected ray of the ray as in the question, we can notice that the reflected ray would be somewhere above the parallel principal axis i.e., ray number $4$ .

Hence, option D is the correct option.

Note: In order to get the desired result, we always need to follow the ray diagram by the use of laws of reflection. Laws of reflection in the case of mirrors are quite important because we need the tangent on the mirror acting as a plane to get all the three rays i.e., incident, reflected ray and the normal.