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H3-21. Sound Resonance In Water Tube


To demonstrate standing waves in a closed tube.


Air column - water reservoir device with tuning fork attached and mallet, as photographed.◙




A tuning fork mounted over the top of the tube is activated by striking it with a rubber hammer. Raising and lowering the reservoir varies the water level in the tube to change the length of the air column. Because the air column is closed on one end (the surface of the water) resonances occur when the length of the tube is approximately 1/4, 3/4 or 5/4 of a wavelength, neglecting the end correction at the top of the tube. Using this apparatus standing waves can be demonstrated and the speed of sound determined to within about one percent. ◙


Jerry L. Underfer, Misconceptions About Resonance In Vibrating Air Columns, TPT 4, 83-85, (1966). ◙Alexander L. Feldman, Resonant Energy Transfer and Coupling Apparatus for Training in Scientific Reasoning, TPT 9, 198, (1971). I. D. Johnston, Standing waves in air columns: Will computers reshape physics courses?, AJP 61, 996-1004 (1993). Bruce Denardo and Steven Alkov, Acoustic resonators with variable nonuniformity, AJP 62, 315-321 (1994).