A vessel ABCD of 10 cm width has two small slits S 1 and S 2 sealed with identical glass plates of equal thickness. The distance between the slits is 0.8 mm. POQ is the line perpendicular to the plane AB and passing through O, the
middle point of S 1 and S 2 , A monochromatic light source is kept at S, 40 cm cm below P and 2 m from the vessel, to illuminate the slits as shown in the figure alongside. After a liquid is poured into the vessel and filled upto OQ, it was found that the central bright fringe is now located at Q.
Calculate the refractive index of that liquid.
Text Solution
Verified by ExpertsA
1.0016
Given Y l = 40 cm, D 1 = 2 m = 200 cm, D 2 = 10 cm
Initial path difference 
& geometrical path difference 
For central maxima, total path difference has to be zero.
i.e., 
Now as central bright fringe is at Q. them the optical path difference is 
=1.0016
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