For a longitudinal wave in air, the excess pressure and displacement a…

Question

For a longitudinal wave in air, the excess pressure and displacement are related such that

Accepted Answer

A. {'text': 'They are exactly out of phase by π/2 rad apart', 'label': 'A'}

1. In a sound wave, pressure variation δp and particle displacement y are related.
2. δp is proportional to the negative of the space derivative of y (from Newton's second law + elastic behaviour).
3. That derivative introduces a π/2 phase shift.
4. So pressure and displacement waves are out of phase by π/2 — pressure nodes are displacement antinodes.
_Source: NCERT Class 11 Physics, Ch 14 "Waves", §14.4_

Answer

{'text': 'They vary exactly in phase with one another everywhere', 'label': 'B'}

Answer

{'text': 'They vary independently with no consistent relation', 'label': 'C'}

Answer

{'text': 'They are always equal in magnitude at every space point', 'label': 'D'}