Question

In a large room, Devyendu receives direct sound wave from a source 120m away from her. She also receives waves from same source which reach her after being reflected from the 25m high ceiling. For which wavelengths will she observe constructive interference of sound?

Solution

The situation is as shown in the figure.

The path travelled by direct wave is,

SD = 120m
The path reflected by reflected wave is,

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equals 2 square root of left parenthesis 60 right parenthesis squared plus left parenthesis 25 right parenthesis squared end root

equals 130 straight m

After reflection, the wave suffers a phase change of π radian which is equivalent to an extra path of 7/2.
The net path difference, between two waves reaching Devyendu is,

space space space increment equals 130 plus straight lambda over 2 minus 120 equals 10 plus straight lambda over 2

For constructive interference,

increment equals nλ.

Thus,

10 plus straight lambda over 2 equals nλ

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∴

space space straight lambda equals 20 comma space 20 over 3 comma space 20 over 5........

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Mechanical Properties Of Fluids

In a large room, Devyendu receives direct sound wave from a source 120m away from her. She also receives waves from same source which reach her after being reflected from the 25m high ceiling. For which wavelengths will she observe constructive interference of sound?

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