Two sources A and B give out sound waves in coherence and in phase. The sources are located at co-ordinates `(0, 0)` and `(0, 9 m)` in `xy` plane. There is a detector located at `(40 m, 0)`. It was found that the detector records continuous increase in intensity of sound when it is moved in positive y-direction for `4.5 m` but the intensity was found to fall for some distance when it is moved in negative y direction. What frequency of sound is consistent with these observations? Speed of sound `= 340 ms^( –1)`.

Answer

`f lt 170 Hz`