In YDSE with `d = 1 mm` and `D = 1 m`, Slabs of `(t = 1 mu m, mu = 3)` and `(t = 0.5mu m, mu = 2)` are introduced in front of upper and lower slits, respectively. Find the shift in the fringe pattern.

Explanation

Optical path for light coming form upper slit `S_(1)` is
`S_(1) p + 1 mu m xx (2 - 1) - S_(2) P + 0.5 mu m`
Similarly, optical path for light coming from `S_(2)` is
`S_(2) P + 0.5 mu m xx (2 -1) = S_(2) P + 0.5 mu m`
Path difference :
`Delta x = (S_(2) P + 0.5 mu m) - (S_(1) P + 2 mu m`
`= (S_(2) P - S_(1) P) - 1.5 mu m`
`= (yd)/(D) - 1.5 mu m`
For Central bright fringe, `Delta x = 0`
`implies y = (1.5 mu m)/(1 mm) xx 1 m = 1.5 mm`
The whole pattern is shifted by 1.5 mm upward.