A glass convex lens is of refractive index 1.55 with both faces of same radius of curvature. What is the radius of curvature required if focal length is to be 20 ~cm ?

Step-by-step solution

Using the Lens maker's formula, aligned & f₁=( -1) ( 1 R₁ - 1 R₂ ) & Here, f=20 ~cm , 1.55, R₁=R, R₂=-R & 1 20 =(1.55-1) ( 1 R - 1 (-R) ) & 1 20 =0.55 2 R & R=1.1 20=22 ~cm aligned