Question

Define the following in context Lens :
1) optical centre
2) principal axis
3) radii of curvature

Answer 1

optical centre is nothing but the pole it's the geometric centre of the sphere of which the mirror forms a part.....
The main line in which Pole and centre of curvature and pole lies......
It is the twice of Focal Length....

Answer 2

Optical center means the central point of a lense.
principal axis:
The straight line passing from pole in horizontal direction
Radii of curvature :
R = 2f
Twice the distance of focal length i.e the distance between the pole to focus and focus to center of curvature

l hope it helps u
tq