Answer:
125.09 Hz
Explanation:
Given : A person stands 5.20 from one speaker and 4.10 m away from the other speaker.
Distance between the speakers is 5.20 - 4.10 =1.10 m
We know that
For destructive interferences
n . λ / 2
where n =1,3,5,7....
Therefore difference between the speakers is
5.10 - 4.20 = 1 X 0.5 λ
λ = 2.2
Given velocity of sound is V = 344 m/s
Therefore frequency, f =
=
= 156.36 Hz
Now, the third lowest frequency is given by
λ = (5.20-4.10) X 5 X 0.5
= 2.75 m
Therefore frequency, f =
=
= 125.09 Hz
Therefore third lowest frequency is 125.09 Hz