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In a large room , a person receives dire...

In a large room , a person receives direct sound waves from a source `120 m` away . He also receives waves from the same source which reach him after being reflected from the ` 5 m` high ceiling at a point halfway between them . For which wavelengths will these two sound waves interfere constructively ?

A

0.21 m

B

0.44 m

C

0.36 m

D

0.45 m

Text Solution

Verified by Experts

The correct Answer is:
A
Length of the path of the reflected wave
` = 2 sqrt( 60^(2) + 5^(2))`
For constructive interference
` 2 sqrt( 60^(2) + 5^(2)) - 120 = n lambda`
or `120.42 - 120 = n lambda or 0.42 = n lambda`
Let ` n = 1 , 2 , 3 , …`
Then ` lambda = 0.42 , 0.21 , .... m`
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