When an object is placed `60 cm` in front of a diverging lens, a virtual image is formed `20 cm` from the lens. The lens is made of a refractive index `mu=1.65` and its two spherical surfaces have the same radius of curvature. What is the value of this radius?

Answer

C

Explanation

`1/v-1/u=1/f=(mu-1)(1/R_1-1/R_2)`
`:. 1/-20-1/-60=(1.65-1)(1/-R-1/(+R))`
Solving we get, `R=39 cm`