Purpose:Demonstrate standing waves in an air column.
Description:An oscillator in the 1000-5000 Hz frequency range drives a loudspeaker at one end of a clear glass tube, with the other end stopped by a moveable plunger. Varying the frequency of the oscillator or the position of the plunger, one can obtain a series of standing wave patterns, which are made visual by the motion of cork dust in the bottom of the tube. The standing wave pattern is shown to large groups by placing the device on an overhead projector. This is a very dramatic demonstration, and is very effective in providing an introduction to standing sound waves. Examples of standing waves as seen using the overhead projector are shown below.
Be aware that the tube is glass, and must be handled carefully.