Kundt's tube

The known Chechen tube allows it to make standing sound waves visible in a glass tube. Standing waves arise, for example, in almost all musical instruments (especially all kinds of flutes and whistles) the sound. The known Chechen tube is named after the physicist August Kundt, whose observations were published in 1866. The simple and intuitive design, the known Chechen pipe is a popular demonstration experiment of physics education.

Construction

In the pipe Lycopodium contained (or ground cork ) are moved by the intense sound wave. The cork dust accumulates it in places where the particle velocity of the sound waves is smallest, that is, in the nodes of the standing wave, where it forms small pile of flour. Thus, the velocity nodes and antinodes of the sound waves become visible. The pile of flour remain even after turning off the sine tone. They are not to be confused with the "Installation" of Korkmehls when the sine wave (with mean amplitudes and volumes of the sine tone, the cork dust rises at the antinodes and remains almost motionless in a mostly comb-like structure. At higher amplitudes, these surveys are not see, because the flour is very whirled to ). Lycopodium can often give you a better picture than from ground cork, as they are lighter and smaller. Thus resonance - i.e., a standing wave - occurs, the length of the tube must pass through a die which can be slid from one side into the pipe, can be adjusted. On the stamp is a closed end (and therefore a vibration node) at the open end of the tube, however, one antinode ago.

Physical Basics

In order to derive when the known chen tube creates a standing wave, the wave speed of sound is considered. One end of the air-filled glass tube is closed by a plunger, the other end is open. Before the open end is the sound source, a very strong speaker. At the open end, the Fast has an antinode, ie maximum deflection, because the open end resonates. The diaphragm of the speaker vibrates in sync with the incoming sound waves. Must be fixed at the closed end, however, a node of the wave are fast, because the end is rigid and therefore does not resonate.

These conditions result, for a given wavelength, only certain tube lengths come in question, at which resonance occurs. The length of the tube must be a multiple of the half wavelength minus one quarter wave length. Thus results for:

By substituting the speed of sound and solving for the resonance frequency is obtained:

For the vibration resonance occurs. The frequency is called fundamental or first harmonic, the other frequencies for first overtone or second harmonic, second harmonic or third harmonic, etc.

Measuring the speed of sound in air

As can be visualized with the aid of the known chen tube sound waves, so the speed of sound can be measured. It follows from the previous equation

In the equation and has been replaced by that we vary the length of the tube at the speed of sound measured at a constant frequency. can be determined by counting the wave crests. Since these are not good but to recognize under certain circumstances, a computational approach offers. The equation has to be set equal to two consecutive resonances at the same frequency to determine.

By measuring and can be determined. Use of the given frequency and in the equation for the speed of sound supplies the finally.