Sounds waves with a wavelength of 0.25 m are emitted coherently (i.e.: in phase

Question

Sounds waves with a wavelength of 0.25 m are emitted coherently (i.e.: in phase with each other) from two sources. These waves are found to interfere constructively at a point P that is 1.60 m from one of the sources. What is the distance from P to the other source? A compact disk uses the interference of reflected waves from the CD to encode information. Light from a red laser ( lambda = 630ww)is reflected from small pits in the CD: and waves from the bottom of a pit and the adjacent top edge interfere. What is the minimum pit depth for which the two waves interfere destructively? Assume this pit is on the surface of the CD so that the region above the pit is air.

Explanation / Answer

Since there is no phase shift between the rays the minimum thickness t = ?/4 where ? = ?o/n

So t = 630nm/(1.6*4) = 98.4nm.

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