Find the focal length of the lens shown in Fig . The radii of curvature of both the surfaces are equal to R.

Explanation

Rays are incident from left
`(mu_3)/(f)=(mu_2-mu_1)/(R_1)+(mu_3-mu_2)/(R_2)`
`R_1=R,R_2=R`
`=(mu_2-mu_1)/(R)+(mu_3-mu_2)/(R)=(mu_3-mu_1)/(R)`
`f=(mu_3R)/(mu_3-mu_1)`