The images produced by spherical mirror may be either real or virtual and may be either larger or smaller than the object. The image can be located by graphical construction as shown in Figure by adopting any two of the following rules.
Fig: Formation of images in concave mirror
(i) A ray parallel to the principal axis after reflection by a concave mirror passes through the principal focus of the concave mirror and appears to come from the principal focus in a convex mirror.
(ii) A ray passing through the centre of curvature retraces its path after reflection.
(iii) A ray passing through the principal focus, after reflection is rendered parallel to the principal axis.
(iv) A ray striking the pole at an angle of incidence i is reflected at the same angle i to the axis.