The sound from a single source can reach point O by two different paths. One path is 20.0 m long and the second path is 21.0 m long. The sound destructively interferes at point O. What is the minimum frequency of the source if the speed of sound is 340 m/s?
A) 340 Hz
B) 6800 Hz
C) 520 Hz
D) 680 Hz
E) 170 Hz

Question

Quizplus · Accepted Answer

Destructive interference occurs when the path difference is an odd multiple of half-wavelengths. The path difference here is 1.0 m. For the first minimum (m=0), the path difference equals half a wavelength: λ/2 = 1.0 m, so λ = 2.0 m. Using v = fλ, where v = 340 m/s, we find f = 340/2 = 170 Hz.

The Sound from a Single Source Can Reach Point O