Optics 6 Question 45

47. In a Young’s double slit experiment, two wavelengths of 500nm and 700nm were used. What is the minimum distance from the central maximum where their maximas coincide again? Take D/d=103. Symbols have their usual meanings.

(2004, 4M)

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Answer:

Correct Answer: 47. 3.5mm

Solution:

  1. Let n1 bright fringe corresponding to wavelength λ1=500nm coincides with n2 bright fringe corresponding to wavelength λ2=700nm.

n1λ1Dd=n2λ2Dd or n1n2=λ2λ1=75

This implies that 7th maxima of λ1 coincides with 5th maxima of λ2. Similarly 14 th maxima of λ1 will coincide with 10th maxima of λ2 and so on.

Minimum distance =n1λ1Dd=7×5×107×103

=3.5×103m=3.5mm



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