Question

Describe the formation of an image of a point object from a plane mirror with the help of a diagram.

Accepted Answer

A mirror with a flat (planar) reflective surface is called a plane mirror. A plane mirror produces images by the regular reflection of light. When an object is placed in front of a plane mirror, its image is formed in the plane mirror. We can locate the image of an object in a plane mirror by using the laws of reflection of light. This can be done as follows. Suppose a small object $O$ (say, a pin-head) which is a point object is placed in front of a plane mirror $M M'$ . An image of this point object will be formed in the plane mirror. We can find out the position of the image of this object in the plane mirror by drawing a ray diagram as follows:

1) We take two diverging rays $O A$ and $O B$ coming from the object $O$ . The rays $O A$ and $O B$ are incident rays that strike the mirror at points $A$ and $B$ making different angles of incidence.

2) The first incident ray $O A$ is reflected by the mirror at point $A$ and goes in the direction $A X$ after reflection (making an angle of reflection $r_{1}$ equal to the angle of incidence $i_{1}$ ). So, $A X$ is the first reflected ray.

3) The second incident ray $O B$ is reflected by the mirror at point $B$ and it goes in the direction $B Y$ after reflection (making an angle of reflection $r_{2}$ equal to the angle of incidence $i_{2}$ ). Thus, $B Y$ is the second reflected ray.

4) The two reflected rays $A X$ and $B Y$ are diverging rays (going apart) that cannot meet in front of the mirror to form a real image. So, we produce the reflected rays $A X$ and $B Y$ backwards (behind the mirror) by dotted lines. On producing backwards, the reflected rays meet at point $I$ behind the mirror as shown in the following figure.

5) When we look into the plane mirror from an angle (as shown in figure ), the reflected rays $A X$ and $B Y$ enter our eye. The reflected rays appear to be coming from point $I$ behind the mirror. So, point $I$ is the image of object $O$ .

Since the reflected rays of light do not actually meet at the image point $I$ but only appear to do so, we say that a virtual image of object $O$ is formed at $I$ . This type of image cannot be obtained on a screen.

Describe the formation of an image of a point object from a plane mirror with the help of a diagram.

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