Propagation and Reflection of Sound in Rarefied Gases. II. Experimental

Abstract

Experiments were conducted to investigate the propagation and reflection of sound in air at low pressures (down to 5 × 10−5 mm Hg). The range of pressures of particular interest are those where the mean free path of intermolecular collisions is longer than the separation between the transmitter and receiver. The frequency range extends from 2 kcps to 12 kcps. Evidence of considerable multiple reflection is found when the separation is small. At larger separation the experimental results are in good agreement with theoretical predictions. The reflection of ``sound'' (i.e., a coherent component of alternating momentum which is partly preserved during molecular encounters with a solid surface) was also verified by using standing wave technique.