Optics Question 848

Question: In an interference arrangement similar to Young’s double-slit experiment, the slits S1 and S2 are illuminated with coherent microwave sources, each of frequency 106 Hz. The sources are synchronized to have zero phase difference. The slits are separated by a distance d = 150.0 m. The intensity I (θ) is measured as a function of θ , where θ is defined as shown. If I0 is the maximum intensity, then I (θ) for is given by

Options:

A) I(θ)=I0/2 for θ=30o

B) I(θ)=I0/4 for θ=90o

C) I(θ)=I0 for θ=0o

D) I=θ is constant for all values of θ

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Answer:

Correct Answer: C

Solution:

[c] We know that I(θ)=I0cos2δ2

where δ=2πdtanθλ

I(θ)=I0cos2(πdtanθπ)=I0cos2(π×150×tanθ3×108/106)

=I0cos2(π2tanθ)

For θ=30o ; I(θ)=Iocos2(π23) For θ=90o ; I(θ)=Iocos2() For θ=0o

I(θ)=I0

I(θ) is not constant.

Alternatively, when θ is zero the path difference between wave originating from S1 and that from S2 will be zero.

This corresponds to a maxima.



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