1.

Two coherent narrow slits emitting sound of wavelengthlambdain the same phase are placed parallel to each other at a small separation of2 lambda. The sound is detected by moving a detector on the screen at a distance D ( gt gt lambda) from the slit S_1 as shown in figure. Find the distance y such that the intensity at P is equal to intensity at O.

Answer»

Solution :LET `Deltax= LAMBDA` at ANGLE `theta` (see fig) Path DIFFERENCE between the waves is `Deltax = 2lambdacos theta`
`:. 2lambda cos theta = lambda (Deltax =lambda) or theta = 60^@`
Now, `PO = S_1O cot 30^@ or y = sqrt 3D`


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