A plane progressive sound wave travels in air along the +x–direction. Answer the following questions in brief but in complete sentences.
(a) Define the term "phase" of a particle executing simple harmonic motion as a part of a travelling wave.
(b) Explain qualitatively how the phase difference between two points situated a distance Δx apart in the direction of propagation is related to their path difference.
(c) Distinguish, with reasons, among the following situations:
(i) the two points are in phase,
(ii) the two points are in opposite phase (antiphase),
(iii) the two points have an arbitrary phase difference Δϕ.
State the corresponding conditions on Δx expressed in terms of the wavelength λ.