In a concave mirror, the principal axis is a line that is perpendicular to the center of the mirror. The easiest way to visualize what a image will look like in this type of mirror is a ray diagram. Before that can be done, the focal point must first be defined. This point is half way between the mirror and the center of curvature on the principal axis. The distance to the focal point from the mirror is called the focal length. We can see from the figure that this focal length is also equal to half of the radius of the curvature. shows the ray diagram of a concave mirror.

Focal .Length

10cm  

15 cm    

20 cm

30cm  

50cm

100CM

Concave             Diameter

A (i)                         50mm

A (ii)                 60 mm

A (iii)                  75 mm

A (iv)                 100 mm