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H1-24. Speed Of Sound In Helium And Sulfur Hexafluoride


To determine the speed of sound as a function of gas density.


Oscillator, small loudspeaker, cardboard tube with cellophane, two microphones, microphone mixer, helium and sulfur hexafluoride tanks, oscilloscope, plastic bag, rods and clamps.

Setup Time

10 min.




Sound pulses passing along the tube encounter two successive microphones, and the oscilloscope measures the time interval between the arrival of the pulse at the two microphones. Having one end covered by thin plastic, the gas tube can be inverted to contain either light or heavy gases. The oscillator is set for a 40 Hz square wave; rhe microphones are 68 cm apart. Approximate values for the speed of sound obtained using this apparatus are: 340 m/s for air, 900 m/s for helium, and 120 m/s for sulfur hexafluoride.


Lecture Demonstration Record Sheet.