In a Young's double slit experiment, the slit separation d is 0.3 mm and the screen distance D is 1m. A parallel beam of light of wavelength 600 nm is incident on the slits at angle α as shown in figure. On the screen, the point O is equidistant from the slits and distance PO is 11.0 mm. Which of the following statement(s) is/are correct ?
(A)For α=π0.36 degree, there will be destructive interference at point O.
(B)Fringe spacing depends on α
(C)For α=π0.36 degree, there will be destructive interference at point P✓ Correct
(D)For α=0, there will be constructive interference at point P.
Answer: (C)
Solution
Path difference at O: Δx=dsinα≈dα (for small α).
With α=1800.36=2×10−3 rad:
λΔx=6×10−7(3×10−4)(2×10−3)=1
This gives constructive interference at O. Option (A) is incorrect.
Fringe spacing β=dDλ is independent of α. Option (B) is incorrect.
At point P:
Δxp=dα+Ddy=3×10−4(2×10−3+11×10−3)=39×10−7
λΔxp=6×10−739×10−7=6.5
This gives destructive interference. Option (C) is correct.
For α=0:
Δxp=Ddy=33×10−7,λΔxp=5.5
This gives destructive interference. Option (D) is incorrect.
JEE Advanced · 2019 · 27 May 2019 · Paper 2 · One or more correct options
