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Question: Answered & Verified by Expert

In a Young's double slit experiment with light of wavelength λ, the separation of slits is d and distance of screen is D such that Ddλ . If the Fringe width is β , the distance from point of maximum intensity to the point where intensity falls to half of the maximum intensity on either side is:

PhysicsWave OpticsJEE MainJEE Main 2015 (11 Apr Online)
Options:
  • A β4
  • B β3
  • C β6
  • D β2
Solution:
1688 Upvotes Verified Answer
The correct answer is: β4
As Imax=4I

Then Inet=12 Imax=2I

2I=2I1+cosϕ

1+cosϕ=1

cosϕ=0

ϕ=π2,3π2,5π2, 

 ϕ=2πλΔx

π2=2πλΔx

Δx=λ4,3λ4,5λ4, 




Also path difference Δx=dsinθ =λ4

At desired location

d ynD=λ4

 yn=λD4d=β4 β=λDd

Separation between central maxima and desired y=β4

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