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Kundt's tube HTML5

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August Kundt was a German physicist who lived in the latter half of the nineteenth century. He made extensive studies of light and sound, two domains where the Physics of waves has a central role.

To study standing sound waves (also known as "stationary sound waves") he used a transparent tube filled with air and a fine powder (talc).

Using a piston striking a membrane at one end of the tube, he looked for conditions that would allow him to obtain standing waves. The nodes and antinodes of the vibrations would be visible in the tube thanks to the talc, which would concentrate at the level of the nodes.

As he wasn't able to vary frequency, he changed the length of the tube instead.

In this simulation, tube length is kept constant and the frequency of excitation can be varied.  This gives the same resuult.  One observes the phenomenon of resonance when the length of the tube (L) and the wavelength of the sound wave produced by the loudspeaker are related in a definite manner.

Rollover the tube`s interior to highlight the motion of the air molecules.

Learning goals

  • To illustrate a standing longitudinal wave.
  • To review the conditions required for resonance.
  • To introduce the Physics of musical instruments that rely on the vibration of a column of air.
  • To calculate the speed of sound.