To find out the position of the image formed by a plane mirror after reflection, take a plane mirror MM’. Now place an extended object AB of size h on the left side of the mirror at a distance u. An incident ray of light AP from the point A of the object AB falls normally on the mirror at point P, and is thus reflected back in the same path, along PA. The second ray of light AO strikes the mirror at point O and gets reflected along the path OC. Now the reflected rays PA and OC are diverging rays and therefore cannot meet each other actually in front of the mirror. So we extend the reflected rays PA and OC backwards behind the mirror by dotted lines. On extending backward these rays appear to meet at point A’ at a distance v. So A’ is the virtual image of point A of the object AB. In the same manner the virtual image B’ will be formed behind the mirror from the incident rays BO and BE falling on the mirror from point B of the object. To get complete image of object AB join the points A’ and B’ by a dotted line. On joining the points A’ and B’ we find that the image formed by a plane mirror is virtual, erect and of the same size as that of object.
Also on measuring the distance of object u and the distance of image v, it is found that the image is formed at the same distance behind the plane mirror as the object is in front of the mirror.
Characteristics of an Image Formed by a Plane Mirror
- Following are the characteristics of an image formed by a plane mirror:
The image formed by a plane mirror is always virtual in nature. - It is erect.
- It is of the same size as the object.
- It is formed at the same distance behind the mirror as the object is in front of the mirror.
Test Your Understanding and Answer These Questions:
- Explain reflection of light from a plane mirror.
- Give the characteristics of image formed by a plane mirror.
- Prove with the help of diagram that the object and image formed in a plane mirror are at equal distance from the mirror.