Young's double slit experiment is first performed in air and then in a medium other than air. It is found…

Young's double slit experiment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in air. The refractive index of the medium is nearly
  1. 1.25
  2. 1.59
  3. 1.69
  4. 1.78

Solution

In air distance of 5th dark fringe is y1
y1=y5th dark =2×5-1λD2d=9λD2d
Also, the distance of 8th bright fringe in the medium is y2=y8th Bright=8λDμd
y1=y2 (according to question)
92λDd=8λDμd
μ=169=1.78

Asked in: NEET 2017

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