Answer:
f = 16.03 kHz
f = 32.07 kHz
Explanation:
For maximum intensity of sound, the two waves must be in phase.
The phase difference (Δ∅) between two waves is given by
Δ∅ = 2πΔr/λ
λ = 2πΔr/Δ∅
where Δr is given by
Δr = r2 - r1
Δr = √(4.5²+0.31²) - 4.5
Δr = 0.0106 m
λ = 2π*0.00106/Δ∅
For cancellation, the phase difference must be Δ∅ = π
λ = 2π*0.0106/π
λ = 2Δr
λ = 0.0212 m
Finally the frequency can be found using
f = c/λ
f = 340/0.0212
f = 16038 Hz
f = 16.03 kHz
Now if the frequency is then increased while you remain 0.31 m from the center, what is the first frequency for which that location will be a maximum of sound intensity?
The λ will be reduced to half
λ = 2Δr/2
λ = Δr
λ = 0.0106 m
f = c/λ
f = 340/0.0106
f = 32075 Hz
f = 32.07 kHz