Question

Define the following:-
(a) Center of curvature (b) Radius of curvature (c) Pole (d) principal axis

(e) Principal focus (f) Focal length

Answer 1

Pole: 
It is the center of the reflecting surface of the concave mirror also called vertex of mirror, generally denoted by letter ‘P’.

Center of curvature: 
It is the center of that sphere of which the concave mirror forms a part, denoted by letter ‘C’.Principal axis: 
The straight line passing through the center of curvature and pole of  concave mirror is called its principal axis.Principal focus:
A beam of light incident parallel to the principal axis, after reflection from the spherical mirror, either actually converges to or appears to diverge from a fixed point on the principal axis. The fixed point is called the ‘Principal focus’, denoted by letter 'F'.

Answer 2

a) Centre of curvature is the centre of the sphere of which the spherical mirror is a part.  (b) Radius of curvature is the linear distance between the pole and the centre of curvature.  (c) Pole is the mid point of a spherical mirror. (d) Principal axis is an imaginary line passing through the pole and the centre of curvature of a spherical mirror. (e) Principal focus is a point on the principal axis, where a beam of light, parallel to the principal axis, after reflection, either actually meets (concave) or appears to meet (convex). (f) Focal length is the linear distance between the pole and the principal axis 
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