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

50,000 `Å`

Explanation

According to the question,
shift = 5 (fringe width)
`:. ((mu -1)tD)/(d) = (5 lambda D)/(d)`
`:. t = (5 lambda)/(mu - 1) = (25000)/(15.1) = 50,000 Å`