Question

A lens forms a sharp image on a screen. On inserting a parallel sided glass slab between the lens and the screen, it is found necessary to move the screen a distance `d` away the lens in order for the image to be sharp again. If the refractive index of the material of the slab is `mu`, the thickness of the slab is
A. `mud`
B. `(d)/(mu)`
C. `(mu-1)/(mu)d`
D. `(mud)/(mu-1)`

Answer 1

Correct Answer - D
Shift`=t(1-(1)/(mu))=d`
`t=(d)/((1-(1)/(mu)))=(mud)/((mu-1))`