Holmarc's Kundt's tube apparatus (Model No: HO-ED-A-02) is a device for measuring the speed of sound. Any waves traveling along the medium will reflect back when they reach the end creating a standing wave allowing harmonics to be identified. Nodes occur at fixed ends and antinodes at open ends. Furthermore, it provides an insight into the interesting phenomenon of standing sound waves.
In this experiment the amplitude of the sound wave can be observed at different locations in the tube, allowing a half wave length to be measured between an adjacent maximum and minimum.
Here, one-side closed cylindrical transparent pipe filled with air is used as a resonator. One end of the tube is attached with a loudspeaker where as the other end is fixed with a movable piston with reflector and a microphone. An AC voltage applied to the loudspeaker, tunes the membrane to vibrations that are transferred to the gas or air column. Frequency can be changed by enlargement or diminishment of the glass cylinder as well as by changing the frequency of the generator.
The velocity of the wave is,
V = ʋ λ
Where υ is the frequency and λ is the wavelength in the case of longitudinal waves, the wavelength is the difference between two consecutive compressions or rarefactions.
A sine wave from an audio oscillator and the signal picked up by a movable microphone to produce Lissajous figures and determine the speed of sound.
Microphone position Vs. Number of wave lengths