Optics Question 901

Question: A parallel beam of light (λ=5000Ao) is incident at an angle α=30 with the normal to the slit plane in YDSE. Assume that the intensity due to each slit at any point on the screen is I0 . Point O is equidistant from S1 and S2 . The distance between slit is 1 mm, then the intensity at

Options:

A) O is 3I0

B) O is zero

C) a point 1 m below O is 4I0

D) a point on the screen 1 m below O is zero

Show Answer

Answer:

Correct Answer: C

Solution:

[c] The path difference at O, Δx=dsinα=dsin30o=1032m

Now ϕ=2πλ.Δx=2π5000×1010×1032=2π×103

So I=Io+Io+2IoIocos(2π×103)=4Io

The angular position of P, tanθ=13 ; or θ=30o .

It means path diffn at P is also Δx

and hence I=4Io



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