As shown in the figure, in Young's double slit experiment, a thin plate of thickness and refractive index is inserted in front of slit . The experiment is conducted in air () and uses a monochromatic light of wavelength . Due to the insertion of the plate, central maxima is shifted by a distance of . is the fringe-width before the insertion of the plate. The value of the is _____.
JEE Physics 2023 Question with Solution
Answer
Correct answer:4
Step-by-step solution
Standard Method
Given: A thin plate of thickness , refractive index , and light of wavelength are used.
Find: The value of in the shift .
When a thin plate is introduced in front of one slit in Young's double slit experiment, the fringe shift is
Substituting the given values,
Hence, .
Therefore, the value of is .
Direct Ratio Method
Given: The shift is written as .
Find: The numerical value of .
Using the fringe shift relation directly,
Now,
Therefore, the value of is .
Common mistakes
Using instead of in the shift formula is incorrect because the extra optical path depends on the excess refractive index over air. Use .
Not converting and into SI units can lead to a wrong ratio. Convert and before substitution.
Confusing the fringe shift with fringe width is incorrect. Here the shift is , so after finding , compare coefficients to get .
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