Question

Calculate equivalent focal length of plano convex lens for following case:-
(i) When curved surface is silvered.
(ii) When plane surface is silvered.

Answer 1

`P = 2P_(L) + P_(M)`
`implies (1)/(F) = (2)/(f_(l)) + (1)/(f_(m)) implies (1)/(F) = (2(mu-1))/(R) + (2)/(R)`
`implies (1)/(F) = (2mu)/(R) implies F = (R)/(2mu)`
(ii)
`P = 2P_(L) + P_(M)`
`implies (1)/(F) = (2)/(f_(L)) + (1)/(f_(M)) implies (1)/(F) = (2(mu-1))/(R) + (1)/(oo)`
`implies F = (R)/(2(mu-1))`