In a large room , a person receives waves from the same source which reach , being reflected from the `25 m` high ceiling at a point halfway between them . The two waves interfere constructively for a wavelength ofA. `20 , 20/3 , 20/5` , etc.B. `10 , 5 , 2.5 `, etc.C. `10 , 20 , 30 `, etc.D. ` 15 , 25 , 35 `, etc.

In a large room , a person receives waves from the same source which r

1.	In a large room , a person receives waves from the same source which reach , being reflected from the `25 m` high ceiling at a point halfway between them . The two waves interfere constructively for a wavelength ofA. `20 , 20/3 , 20/5` , etc.B. `10 , 5 , 2.5 `, etc.C. `10 , 20 , 30 `, etc.D. ` 15 , 25 , 35 `, etc.
Answer» Correct Answer - B Length of the path for direct sound ` = 120 m` Length of the path for reflected sound ` = 2 sqrt((60)^(2) + (25)^(2)) = 130 m` Geometrical path difference ` = 130 - 120 = 10 m` Two waves interfere constructively when `10 = n lambda` Putting , `n = 1 , 2, 3,..., lambda = 10 , 5 , 2.5 , .....`

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