Question

An object lies in front of a thick parallel glass slab, the bottom of which is polished. If the distance between first two images formed by bottom surface is 4cm then find thickness of glass slab.(Assume n of glass=1.5 and paraxial rays)

Answer 1

Shift of an object due to a thick glass slab is given by

$\delta = t(1 - \frac{1}{\mu})$

given that distance between two images is 4 cm

so shift = 4 cm

$\mu = \frac{3}{2}$

now by above formula we have

$4 = t * (1 - \frac{1}{3/2})$

$4 = t*(1 - \frac{2}{3})$

$4 = \frac{t}{3}$

by solving above

t = 12 cm

so thickness of glass slab is 12 cm