# Doubt from Sound

Sorry for the late reply @Viram_2019 sir ..yes it is the correct answer..pls tell how you got it..

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For any point X on line P Q. As X tends to infinity, the path difference between waves from D1 and D2 tends to 0.

From this, we can say that Q corresponds to first minima with path difference = \cfrac{\lambda}{2}

Hence P corresponds to a path difference of \cfrac{3\lambda}{2}

Then we can calculate D_1P-D_2P = \cfrac{3\lambda}{2}

Solve for wavelength and then frequency(\approx 116 Hz).

Closest answer is option 4.

PS: Sorry for the delay in my reply as well. Got busy with college registration post vacation.

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