Two loudspeakers emit 850Hz sound waves in phase. A microphone is located 12.0m from one speaker and 14.0m from the other. The speed of sound is 340ms−1. Which type of interference will the microphone detect?
(a) Destructive interference, because the path difference of 2.0m is less than one wavelength, so the crest from one speaker meets the trough from the other.
(b) Constructive interference, because the waves are emitted in phase and therefore remain in phase at all points.
(c) Constructive interference, because the 2.0m path difference equals 5λ, an integer multiple of the wavelength.
(d) Destructive interference, because an odd multiple of the wavelength (such as 5λ) produces a 180∘ phase difference.