Question

A plano-convex lens of focal length 30 cm has its plane surface silvered. An object is placed 40 cm from the lens on the convex side. The distance of the image from the lens is
A. 18 cm
B. 24 cm
C. 30 cm
D. 40 cm

Answer 1

Correct Answer - B


`(1)/(F)=(1)/(f_l)+(1)/(f_m)+(1)/(f_l)`
`=(2)/(f_l)+(1)/(infty)=(2)/(30)impliesF=15cm`
The silvered lens behaves as concave mirror of focal length `15 cm`
`(1)/(v)+(1)/(u)=(1)/(f)implies(1)/(v)+(1)/(-40)=(1)/(-15)`
`(1)/(v)=-(1)/(15)+(1)/(40)=(-8+3)/(120)impliesv=-24cm`