The radius of the convex surface of planoconvex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length is

Step-by-step solution

Using the relation for focal length of planoconvex lens = 1 f =( -1) ( 1 R₁ - 1 R₂ ) (Refractive index of material of lens =1.5 , .R₁=20 ~cm , R₂= ) aligned 1 f & =(1.5-1) ( 1 20 - 1 ) 1 f & = 1 40 or f & =40 ~cm aligned