TOPIC 3 LIGHT Rules of reflection in a concave mirror
1. Any incoming ray that hits the pole will reflect at an angle r equal to the size of angle i (Fig. 13.4; the principal axis can be considered the normal as it is perpendicular to the mirror surface).
pole C F
FIG. 13.4
2. Any incoming ray passing through the focal point F will reflect back parallel to the principal axis (Fig. 13.5).
C F
FIG. 13.5
3. Any ray running parallel to the principal axis will reflect back through the focal point F (Fig. 13.6).
C F
FIG. 13.6
4. Any incoming ray passing through C will reflect back along its original path (Fig. 13.7; because C is the centre of the theoretical sphere,
any line from C to the mirror is a radius and hence an axis, so that i = r = 0° from the normal).
