Purpose:Demonstrate standing waves in a closed tube.
Description:An air column in a tube is excited by an oscillator and loudspeaker at one end of the tube and stopped with a plunger at the other end. Vary the frequency of the oscillator or the position of the plunger to obtain the resonance, which can be easily heard. Because this is a closed tube, resonances exist at odd multiples of one-quarter wavelength. Using this device standing waves can be demonstrated, the wavelength of a sound wave shown, and the speed of sound determined.
Invite students to make predictions about the changing resonant frequencies before adjusting, to encourage student engagement.