Speed of Sound from an Open–Open Resonance Tube
A fixed air column open at both ends; the model hides the true speed of sound. Tune to harmonic n, read noisy resonance frequencies fₙ, recover v from v = 2 fₙ L / n and average.
Goal
Determine the speed of sound v in air from the open–open resonance condition fₙ = n v / (2L) using several harmonics n and the sample mean of vₙ = 2 fₙ L / n.
Equipment
- Resonance tube (open–open), L = 1.1 m
- Sine excitation / frequency readout (simulated)
- Harmonic selector n
Theory
For a tube open at both ends, pressure nodes occur at the ends; allowed standing waves have harmonics fₙ = n v / (2L) with n = 1, 2, 3, … Rearranging gives v = 2 fₙ L / n. Small frequency-reading error is modelled on each measurement.
Procedure
- The apparatus uses a fixed column length L = 1.1 m (shown on the card) with both ends open, matching the “open at both ends” case in the related simulator.
- Select the harmonic index n with the slider (use several different values from 1 upward).
- Press “Record measurement” to log (n, fₙ): the frequency reading carries small tuner noise.
- Repeat for at least 5 distinct harmonics spread across the available n range.
- The table adds v = 2 fₙ L / n for each row. Take the sample mean of v as your result.
- Compare with the reference speed of sound in air and write the conclusion.
Experiment
Conclusion
The mean speed of sound agrees with the reference value within tolerance. Main uncertainties: tuning/readout of fₙ, end corrections not included, and assuming a uniform air column at room temperature.