Interference pattern with Young's double slits 1.5mm apart are formed on a screen at a distance 1.5m from the plane of slits. In the path of the beam of one of the slits, a transparent film of 10 micron thickness and of refractive index 1.6 is interposed while in the path of the beam from the older slit a transparent film of 15 micron thickness and of refractive index 1.2 is interposed. Find the displacement of the fringe patten.

Explanation

Shift = ` ((mu-1)tD)/d`
`S_1 = ((1.6-1)(10xx10^-6)(1.5))/(1.5 xx 10^-3) `
` = 0.6 xx 10^-2m `
` = 0.6m`
` S_2 = ((1.2-1)(15 xx 10^-6)(1.5))/(1.5 xx 10^-3)`
` = 0.3 xx 10^-2m`
0.3cm
` = DeltaS = S_1-S_2 = 0.3 cm`
= 3mm.