Find the focal length of the lens shwon in figure
(a) If the light is incident form left side.
(b) If the light is incident form right side.

Explanation

(a) `(1)/(f) = (n_("net") - 1) ((1)/(R_(1)) - (1)/(R_(2))) = ((3)/(2) - 1) ((1)/(-60) - (1)/(-20))`
`f = 60cm`
(a) `(1)/(f) = (n_("net") - 1) ((1)/(R_(1)) - (1)/(R_(2))) = ((3)/(2) - 1) ((1)/(20) - (1)/(60))`
`f = 60cm`