Question

A girl is 4m away from the plane mirror. If she moves a few steps closer to the mirror, what will happen to the image size in the mirror?

A) The size of the image will decrease.
B) The size of the image will increase.
C) The size of the image will be the same.
D) Cannot say.

Answer 1

Hint: This question can be solved by using the basic knowledge about the nature of image formation in case of plane mirror.

Complete step by step answer:To solve this question, we must know the nature of image formation in the case of plane mirrors.
When we stand in front of a mirror, we can see our own image behind the mirror. We observe that the image will be formed exactly at the same distance from the mirror as the distance between mirror and self. i.e. object distance is equal to the image distance. If we stand 1m away from the mirror, then the image also formed 1m behind the mirror. Also, if we raise our right hand, in the image it looks like we raised our left hand. The image appears to be laterally inverted. The image formed behind the mirror is always a virtual image. Our height also is the same in the image. The object size is always equal to the size of the image formed behind the mirror. But in the given question the person moves towards the mirror. This can be analysed by us easily by trying in front of a mirror. You stand in front of the mirror and move towards the mirror slowly; you can observe that your image looks bigger and bigger as you move towards the mirror. But actually, the size of the image is not increasing at all, it appears to be increasing as you are moving towards the mirror. The size of the image is always equal to the size of the object.
We also compare this to a general scenario that if any object is moving towards us, we feel the size of the object increasing. But as it moves towards us it looks like it has increased.
Hence, in this question a girl is already at a distance of 4m from the mirror, as she moves towards the mirror the size of the image formed behind the mirror equals the size of the girl.
Hence, the correct answer is (C)

Note:In this case, we may feel that the size of the image will increase as the girl moves towards the mirror. But we have to keep in mind that the image size is equal to the size of the object. Since the object (girl) is moving towards the mirror it looks like image size increased. Actually, it is not increasing.