Question

A plane mirror reflects a pencil of light to form a real image. Then the pencil of light incident on the mirror is
A. Parallel
B. Convergent
C. Divergent
D. None of these

Answer 1

Recall the images formed by the plane mirror for different types of incident rays. Also, recall the condition of the incident ray for which a real image is formed by the plane mirror.

Complete step by step answer: The angle of incidence and the angel of reflection for the light incident on the plane mirror are equal.

When a parallel ray of light is incident on a plane mirror, the light gets reflected from the mirror and retraces its path. Hence, no image is formed if the light incident on the plane mirror is parallel.

Therefore, the real image is not formed by the parallel pencil of light incident on the plane mirror.

Hence, the option A is incorrect.

The image of a real object formed by the plane mirror is always virtual and behind the mirror.

Hence, when a divergent ray of light is incident on a plane mirror, the image of the object formed is virtual.

Therefore, the real image is not formed by the divergent pencil of light incident on the plane mirror.

Hence, the option C is incorrect.

If the pencil of light incident on the plane mirror is convergent, the image formed is a real image.

Hence, the option D is incorrect.

The image of a real object formed by the plane mirror is always virtual and behind the mirror. But it can be real only if the incident ray of light is convergent.

When the pencil of light is incident on the plane mirror in such a way that the reflected rays converge, the image formed by the pencil light is a real image.

The ray diagram illustrating this situation is as follows:

From the above ray diagram, it can be seen that if the pencil of light is made to converge after reflection from the mirror, the image formed is a real image.

Hence, the correct option is B.

Note: The plane mirrors always form a virtual image of the real objects. But the image formed is also real if the object is virtual.