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. [5 Marks]

Answer 1

Suppose a point-sized object is placed at A as shown below:

[2 Marks]

For the ray starting from point A and travelling in the horizontal direction towards point D, the angle of incidence is 0 degree and hence it retraces its path. Similarly, the ray starting from A and travelling towards point C, follows the law of reflection. When these rays are produced backward they appear to meet at a point E which is the image of point A. This is a virtual image as the rays don't actually meet. [1 Mark]

Characteristics of the image formed by a plane mirror :

• It is virtual and erect. [0.5 Marks]
• It is erect and of the same size as the object. [0.5 Marks]
• The distance of the object from the plane mirror is same as the distance of the image from the plane mirror. [0.5 Marks]
• The image is laterally inverted. [0.5 Marks]