of reflection are the same for the two extreme reflections. The normals are now the bisectors of the angles between the incident and the reflected rays at the two points. By geometry, the height of the mirror needed is only half of the height of the person. h h h Does the height depend on the distance between the person and the mirror?
SPHERICAL MIRRORS We shall now study about the reflections that take place in spherical surfaces. A spherical surface is a part cut from a hollow sphere. Spherical mirrors are generally constructed using glass. One surface of the glass is silvered.
The reflection takes place at the other surface which is polished. If the polished surface of the mirror is convex it is called as convex mirror. These are shown in Figure . .
We shall get familiarised with some of the terminologies pertaining to spherical mirrors. . C P P Hollow sphere Reflecting surface Spherical mirrors Figure . Spherical mirrors Outer reflective A convex mirrors Inner reflective A concave mirrors - - - - Unit ray optics Focus (or) Focal point : Light rays travelling parallel and close to the principal axis when incident on a spherical mirror, converge at a point for concave mirror (or) appear to diverge from a point for convex mirror on the principal axis.
This point is called the focus ( or) focal point F of the mirror. Focal length : The distance between the pole P and the focus F is called the focal length f of the mirror. Focal plane : The plane through the focus and perpendicular to the principal axis is called the focal plane of the mirror. All the above mentioned terms are shown in Figure .
for both concave and convex mirrors. C F P R (a) P F C R (b) Figure . Representation of terminologies for (a) concave and (b) convex mirrors . .
Paraxial Rays and Marginal Rays The paraxial rays are the rays which travel very close to the principal axis and make small angles with it .