Question

how focal length and radius of curvature are related to each other

Answer 1

focal length = Radius of curvature/2

Answer 2

The focal length (f) of a lens is the distance between the center of the lens and the point at which the reflected light, of a beam of light travelling parallel to the center line, meets the center line (principal axis). The radius of curvature (r) is the radius of the lens that forms a complete sphere..

Now as u can see r=2f
so we can conclude that radius of curvature is twice the focal length ..