Image Formation by Spherical Mirrors

The ray diagram for image formation by mirrors can be drawn by taking any two of the following rays. The point where these two rays meet or appear to be coming from the point will be the image point which determines the position of image.

1. Ray striking the pole: The ray of light striking the pole of the mirror at an angle is reflected back at the same angle on the other side of the principal axis.

2. Parallel ray: For concave mirror the ray parallel to the principal axis is reflected in such a way that after reflection it passes through the principal focus. But for a convex mirror the parallel ray is so reflected that it appears to come from principal focus.

3. Ray through centre of curvature: A ray passing through the centre of curvature hits the mirror along the direction of the normal to the mirror at that point and retraces its path after reflection.

4. Ray through focus: A ray of light heading lowards the focus or incident on the mirror after passing through the focus returns parallel to the principal axis.

Formation of image by concave mirror

Using the above rules of image formation, the ray diagram for the image formed for different positions of an object are given below:

Formation of image by convex mirror

Image formation in convex mirror is:


The position, nature and size of the image formed in concave mirror and convex mirror can be summarized as:

# Object Position Image Position Nature Size
  Concave Mirror      
1 Between P & F Behind the mirror Virtual Larger
2 At F At infinity Real Enlarged
3 Between F & 2F Beyond 2F Real Larger
4 At 2F At 2F Real Same size
5 Beyond 2F Between F & 2F Real Smaller
6 At infinity At F Real Diminished
  Convex Mirror      
7 Anywhere Between P & F Virtual Smaller