A biconvex lens `(mu=1.5)` has radius of curvature `20cm` (both).
find its focal length.

Answer

B, C

Explanation

`R_1=+20cm, R_2=-20cm, mu=1.5`
Substituting the values in the equation
`(1)/(f)=(mu-1)((1)/(R_1)-(1)/(R_2))`, we have
`1/f=(1.5-1)(1/20-1/-20)`
or `f=+20cm`