Question

In YDSE, find the thickness of a glass slab `(mu=1.5)` which
should be placed in front of the upper slit `S_1` so that the central maximum now
lies at a point where 5th bright fringe was lying earlier (before inserting the
slab). Wavelength of light used is `5000 Å`.

Answer 1

According to the question,
Shift = 5(fringe width)
`:. ((mu-1)tD)/d = (5lambdaD)/d `
` :. t= (5lambda)/(mu-1) = 25000/(1.5-1)`
= 50000Å.