Halliday, Resnick & Walker — Waves–II: Problem 20

Figure 17.12 shows four isotropic point sources of sound that are uniformly spaced on an x axis. The sources emit sound at the same wavelength \(\lambda\) and same amplitude \(s_m\), and they emit in phase. A point P is shown on the x axis. Assume that as the sound waves travel to P, the decrease in their amplitude is negligible. What multiple of \(s_m\) is the amplitude of the net wave at P if distance \(d\) in the figure is (a) \(\lambda/4\), (b) \(\lambda/2\), and (c) \(\lambda\)?