If keeping an object fixed a plane mirror is rotated in its plane by an angle θ, then the reflected ray rotates in the same direction by an angle 2 θ.
Focal length as well as radius of curvature of a plane mirror is infinity. Power of a plane mirror is zero.
An image formed by a plane mirror is virtual, erect, laterally inverted, of same size as that of object and at the same distance as the object from the mirror.
( ii) Spherical Mirror A highly polished curved surface whose reflecting surface is a cut part of a hollows at glass sphere is called a spherical mirror. Spherical mirrors are of two types
( a) Concave Mirror A spherical mirror whose bent in surface is reflecting surface, is called a concave mirror.
( b) Convex Mirror A spherical mirror whose bulging out surface is reflecting surface, is called a convex mirror.
Some Terms Related to Spherical Mirrors are Given Below
( i) Centre of Curvature It is the centre of the sphere of which the mirror or lens is a part.
( ii) Radius of Curvature( R) The radius of the hollow sphere of which the mirror is a part, is called radius of curvature.
( iii) Pole The central point of the spherical mirror is called its pole( P).
( iv) Focus When a parallel beam of light rays is incident on a spherical mirror, then after reflection it meets or appears to meet at a point on principal axis, which is called focus of the spherical mirror.
( v) Focal Length The distance between the pole and focus is called focal length( f). Relation between focal length and radius of curvature is given by