Question

A double convex lens is made of a glass of refractive index 1.55 with both faces of same radius of curvature find the radius of curvature required if the focal length is 20 cm

Answer 1

I guess we know the relation between radius of curvature of a sphere and its focal length , that is

r =2f

Then ,

Given:- f=20cm

So,

r = 2(20)

r= 40cm.