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Inquiry: Tubes

Purpose: To determine the best resonant length of a closed tube for sounds of known frequencies.


Resonance, or sympathetic vibration, occurs when the natural vibration rates of two objects are the same. The air column in a closed glass tube produces its best resonance when it is approximately one-fourth as long as the wavelength of the sound. A small correction in wavelength must be made for the internal diameter of the tube. The wavelength of the sound may be calculated from this resonant length of the tube by the formula: wavelength = 4(L + .4d). In this experiment, the best resonant length of a closed tube will be determined. From this length and the diameter of the tube, the wavelength will be calculated. The speed of the sound can then be calculated.

Open Tubes

Closed Tubes

Determine the speed of sound using three different tuning forks and then the room temperature.

Inquiry Questions:

  1. Explain what harmonics you get with closed tubes and why?

  2. Explain what harmonics you get with open tubes and why?

  3. Best resonance is found when a tuning fork is placed over a 24.0 cm closed tube with a diameter of 4.00 cm. What is the wavelength of the sound in the air?