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JEE Advanced 2016 Paper 2

Section: Physics

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Question : 7 of 54

Marks: +1, -0

While conducting the Young's double slit experiment, a student replaced the two slits with a large opaque plate in the x-y plane containing two small holes that act as two coherent point sources

S_1,S_2

emitting light of wavelength 600 nm. The student mistakenly placed the screen parallel to the x-z plane (for

z > 0

) at a distance

D =3\,\text{m}

from the mid- point of

S_1,S_2

as shown schematically in the figure.The distance between the sources d

=0.6003

.The origin O is at the intersection of the screen and the line joining

S_1,S_2

Which of the following is (are) true of the intensity pattern

[JEE Adv 2016 P2]

Hyperbolic bright and dark with foci symmetrically placed about O in the x-direction
Semi circular bright and dark bands centered at point O
The region very close to the point O will be dark
Straight bright and dark bands parallel to the x-axis

Solution:

Path difference at point O = d = .6003 mm = 600300 nm

\frac{2001}{2}(600\text{nm}) = 1000\lambda + \frac{\lambda}{2}

⇒ minima from point O

Line

S_1S_2

and screen are ⊥ to each other so fringe pattern is circular (semi-circular because only half of screen is available)

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