Two identical coherent sound sources are placed a small distance apart on level ground. A listener walks slowly along a straight path perpendicular to the line joining the sources and notices an alternation of loud and weak sounds.
(i) Explain qualitatively why the listener hears this pattern of alternating loudness.
(ii) State the path-difference conditions for (a) maximum loudness and (b) minimum loudness.
(iii) Using a labelled diagram of two equal vectors, illustrate how the resultant displacement amplitude differs in the two cases.