Two transparent slabs having equal thickness but different refractive indices μ1 and \mu2 are pasted side by side to form a composite slab. this slab is placed just after the double slit in a young's experiment so that the light from the other slit goes through the other material. What should be the minimum thickness of the slab so that there is a minimum at the point P0 which is equidistant from th eslits ?
The change in path difference due to the two slabs is (μ1−μ2) t (as in problem N o. 16) for having a minimum at p, the path
Difference should change by 12
So, λ2=(μ1−μ2)t⇒t=λ2[μ1−μ2]