Find focal length of the system as shown if figure.
Find image position.

Answer

+40 cm

Explanation

(a) `mu_1=1, mu_2=1.5, R_1=R=+40cm and R_2=oo`
Using the formula,
`1/f=(2(mu_2//mu_1))/R_2-(2(mu_2//mu_1-1))/R_1`
`=(2(1.5))/oo-(2(1.5-1))/40`
or `f=-40cm`
Thus, the given system behaves like a concave mirror of focal length `40cm.`
(b) Using the mirror formula, we have
` :. 1/v+1/u=1/f`
`1/v+1/-20=1/-40`
`:. v=+40cm`
Therefore, image will be formed at a distance of `40cm` to the right hand side of the given
system.