Measurements of the Range Dependent Sound Velocity in Argon at Very Low Pressure

The sound velocity was measured in Argon at a frequency of 200 kHz and at a pressure of about 0,03 Torr. Under these conditions, the mean free path A of the molecules is of the same magnitude as the distance x between sound transmitter and receiver. Then, the sound velocity depends on the measuring distance x, and the assumptions for the “classical” theory of sound are no longer valid. Meyer and Sessler [13] have developed a theory for this region and they have verified it by some measurements in air. By use of a different method of measurement, it was possible to investigate this theory in Argon over an extended measuring range. The results are in satisfactory agreement with the theory of Meyer and Sessler.