DEMONSTRATION 12.2 Demonstration of the Second Law of Reflection
Apparatus Plane mirror, raybox, pins, sheet of cardboard, protractor
Procedure Set up apparatus as illustrated in Fig 12.5. Draw a line along the back of the mirror. Mark the position of the rays using pins. Remove raybox and mirror, draw the lines representing the incident and reflected rays and normal at the point of incidence.
Measure the angles of incidence and reflection. Observation
The angles of incidence and reflection are equal.
Conclusion Law 2 is verified.
Fig 12.5
Reflection of Light from Spherical Mirrors
Concave mirror
Centre of curvature
Principal axis C
Reflecting surface
Focus F
Pole P Focal length = f
Reflecting surface
Pole Principal axis P
Focus F
Focal length = f Convex mirror Centre of
curvature C
Fig 12.6:Terms used for spherical mirrors
TERMS USED TO DESCRIBE SPHERICAL MIRRORS The pole (P) of a spherical mirror is its centre point.
The centre of curvature (C) of the mirror is the centre of the sphere from which the mirror is made.
The principal axis is the straight line joining the pole to the centre of curvature.
The focus or focal point (F) is the point halfway between the centre of curvature and the pole. The focal length (f ) is distance from the focus to the pole.
