Find the focal length of a convavo-convex lens (Positive me menisus ) with `R_(1) = 15cm`, and `R_(2) = 25cm`. The refractive index of the lens material `n = 1.5`m
`(1)/(f) = (1.5-1)((1)/(15)-(1)/(25)) = 0.5((10-6)/(150)), :. F = (300)/(4) = 75cm`

Explanation

`(1)/(f) = (1.5-1) ((1)/(15)-(1)/(25)) = 0.5((10-6)/(150)), :. f = (300)/(4) = 75cm`