Answer the following questions :
Draw a figure explaining various terms related to a lens.

Explanation

i. Principal axis: The imaginary line passin through both centres of curvature is called th! principal axis of the lens.
ii. Optical centre: The point inside a lens on the principal axis, through which light rays pass without changing their paths is called the optical centre of a lens.
iii. Centre of curvature: The centre of sphere whose part forms the surface of the lens is called centre of curvature of the lens.
iv. Radius of curvature: The radius of the sphere whose part forms the surface of the lens is called radius of curvature of the lens.
v. Principal focus:
a. When light rays parallel to the principal axis are incident on a convex lens, they converge to a point on the principal axis. This point is called the principal focus of the lens.
b. Rays travelling parallel to the principal axis of a concave lens diverge after refraction in such a way that they appear to be coming out of a point on the principal axis. This point is called the principal focus of the concave lens.
vi. Focal length: The distance between the optical centre and principal focus of a lens is called its focal length.