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Question: Answered & Verified by Expert

In a special arrangement of Young's double-slit experiment, the distance between the slits d is twice the distance between the screen and the slits D, i.e d=2D. For this setup, the value of D such that the first minima on the screen fall at a distance D from the centre O is found to be λN.

What is the value of N? [Take 5=2.24

PhysicsWave OpticsJEE Main
Solution:
1405 Upvotes Verified Answer
The correct answer is: 2.48

From diagram as provided in question, OP=x
CO=D
S1C=S2C=DT1P=T1O-OP=D-x
T2P=T2O+OP=D+x
Now, S1p=S1T12+T1 P2=D2+D-x2

S2P=S2T22+T2P2=D2+D+x2

For fist minimum to occur,

Path difference

S2P-S1P=λ2

D2+D+x2-D2+D-x2=λ2

The first minimum falls at a distance D from the centre, i.e., x=D

D2+4D212-D=λ2

D5-1=λ2

D=λ22.24-1=λ2.48

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