Image Formation in Plane Mirror

To understand the formation of image, you may consider the light rays emerging out of the object A. The three rays namely (a), (b), and (c) after striking the mirror M1M2 get reflected in the direction (d), (e) and (f), respectively obeying the laws of reflection.

These reflected rays never meet with each other in reality. However, they appear to be coming emerging out from the point A′, inside the mirror. If the reflected rays (d), (e) and (f) are extended in the backward direction, they will appear to meet with each other at A′.

Thus at A′ we get the image of object A.

The image formed by a plane mirror has the following characteristics:

  1. This image is virtual (i.e. it is not real), erect and the same in size as the object.

  2. The object distance and the image distance from the mirror are found to be equal. OA = OA′

Hence, the image of a point in a plane mirror lies behind the mirror along the normal from the object, and is as for behind the mirror as the object is in front. It is an erect and virtual image of equal size.

Few facts about reflection

Due to reflection in a plane mirror left handedness is changed into right handedness and vice-versa. This is known as lateral inversion. However, the mirror does not turn up and down. The reason for this is, that the mirror reverses forward and back in three dimensions (and not left and right), i.e., only z-direction is reversed resulting in the change of left into right or vice-versa.

In a plane mirror the distance of the image is same as the distance of object from the mirror. If object distance from the mirror changes, the distance of image from the mirror will also change in the same way. It means if an object moves with velocity v towards the mirror, image will also move with same velocity v towards the mirror and at every time the distances of the object and image from the mirror remain equal. However, the velocity of image towards the object will be 2v.

You can see your full image in a plane mirror whose height is half of your height.