The direction of ray of light incident on a concave mirror is shown by PQ while directions in which the ray would travel after reflection is shown by four rays marked 1, 2, 3 and 4 (Fig 9.1). Which of the four rays correctly shows the direction of reflected ray?

Question

Philoid · Accepted Answer

For spherical mirrors, a ray that passes through the focus (or appears to pass through the focus) emerges parallel to the principal axis after reflection.

In this diagram, we have a ray PQ that reflects from a spherical mirror. PQ passes through the focus (labelled ‘F’). Now, the principal axis is the one that is passing through the centre (labelled ‘C’) of curvature and focus (labelled ‘F’). The reflected ray should be parallel to CF. The only such ray is 2. Hence, option (b) is the correct answer.