Define the following terms : Centre of curvature, Radius of Curvature, Principal Axis, Optical Centre , Principal Focus , Focal length & Focal plane .
1. Centre of curvature: The centre of curvature is the center of the sphere from which a curved mirror or lens is derived. For a concave mirror or a convex lens, it is the center of the sphere of which the reflecting surface or the refracting surface is a part.
2. Radius of curvature: The radius of curvature is the distance between the centre of curvature and the vertex (the geometric center) of a curved mirror or lens. It is denoted by the symbol 'R'.
3. Principal axis: The principal axis is...