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Question
With the help of a labelled ray-diagram, describe how a plane mirror forms an image of a point source of light placed in front of it. State the characteristics of the image formed in a plane mirror.
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Solution
Consider a small object (a point source of light), placed in front of a plane mirror MM' (figure 1). The mirror will form an image I of the object O. This process of image formation is explained as follows:
The object O gives out light rays in all directions. Now, a ray of light OA, coming from the object O, is incident on the plane mirror at point A. OA gets reflected in the direction AX in accordance with the law of reflection, which states that the angle of reflection r1 equals the angle of incidence i1. Another ray of light OB, coming from the object O, strikes the mirror at point B. OB gets reflected in the direction BY, thus, making the angle of reflection r2 equal to the angle of incidence i2.
The two reflected rays AX and BY are divergent and cannot meet on the left side. Let's produce the reflected rays AX and BY backwards. They meet at a point I behind the mirror. When the reflected rays AX and BY enter the eye of a person at position E, the eye sees the rays in the direction in which they enter. So, the person looking into the mirror from position E sees the reflected rays as if they are coming from the point I behind the mirror. Thus, the point I is the image of the object O formed by the plane mirror.
The image produced by the plane mirror is virtual, laterally inverse and of the same size as the object.
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