(a) Incident rays travelling parallel to the principal axis are reflected back through the focus. (b) Incident rays passing through the focus are reflected back parallel to the principal axis. (c) Incident rays passing through the centre of curvature are reflected back along their own path.
(a)
(b) Fig 12.7: Rules of reflection for concave mirrors Rules of reflection for convex mirrors
(a) Incident rays travelling parallel to the principal axis are reflected so as to appear to be coming from the focus.
(b) Incident rays heading for the centre of curvature are reflected back along their own path.
(a) Finding the Position and Nature
of Image by ‘Ray-tracing’ The position and nature of an image in a spherical mirror can be found by ‘ray-tracing’. This means drawing rays of light from the object to the mirror and applying the rules outlined above.
Concave, object beyond C
The image is 1. Between C and F 2. Real 3. Inverted 4. Diminished
Concave, object at C
The image is 1. At C 2. Real 3. Inverted 4. Same size as the object
Concave, object between C and F
The image is 1. Beyond C 2. Real 3. Inverted 4. Magnified
Fig 12.11: Ray diagram for a concave mirror, object between C and F
REFLECTION OF LIGHT 199 (b)
Fig 12.8: Rules of reflection for convex mirrors
(c)
Fig 12.9: Ray diagram for a concave mirror, object beyond C
Fig 12.10: Ray diagram for a concave mirror, object at C
