Problem C13:
Two speakers are producing sinusoidal sound coherently in phase. The speakers
are separated by a distance of n_{1}, and the wavelength of the sound
is n_{2}. See the figure below. At the point A, the waves are
in phase and the intensity is I_{A}. The point B is located
"in line" with the two speakers, and the same distance away from the center
of the speakers as point A. What is the sound intensity at the point
B? If the sound intensity at the point B is
I_{B} = I_{A}/n_{3},
what is n_{3}? Note that n_{1} and n_{2} have the same units
of length, and n_{3} is unitless.

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