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In YDSE a parallel beam of incident light consists of two wavelengths λ1=4000 A andλ2=5600 A. The minimum distance y on the screen, measured from the central axis, where the bright fringe due to two wavelengths coincide is n λ 1 D d . Find n.

PhysicsWave OpticsJEE Main
Solution:
1668 Upvotes Verified Answer
The correct answer is: 7
n 1 X ¯ 1 = n 2 X ¯ 2

n 1 D λ 1 d = n 2 D λ 2 d

n 1 λ 1 = n 1 λ 2

λ 1 λ 2 = n 2 n 1 = 4000 5600 = 40 58 = 5 7

n 2 n 1 = 5 7 X 1 X 2 = 7 5

y = 7 X ¯ 1 = 7 D λ 1 d

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