Speed of sound with a resonance tubeStarter example
A starter example, adapted by LABKickstart from the OpenStax College Physics for AP Courses Lab Manual and shared under CC BY 4.0. It is not a classroom submission from a teacher on Benchtop.
Hold a struck tuning fork over a column of air and change the column length until the note jumps in volume. That resonance length gives you a wavelength, and the wavelength gives you the speed of sound.
Materials
- Tall graduated cylinder or a resonance tube
- Water
- Two or three tuning forks of known, clearly different frequencies
- Rubber mallet or a rubber stopper to strike the forks
- Centimetre rule
- Thermometer to record room temperature
Procedure
- Fill the cylinder most of the way with water so the air column above it can be varied.
- Strike a tuning fork on the rubber mallet and hold it flat over the mouth of the cylinder without touching the rim.
- Raise or lower the water level, or the tube, until the note is clearly loudest. Record that air column length.
- Keep going to find the next resonance further down, and record it too.
- The first resonance is a quarter of a wavelength, so multiply by four to get the wavelength. Compute speed as frequency times wavelength.
- Repeat for each fork, then record the room temperature and compare your average speed with the accepted value for that temperature.
Expected results
Resonances appear at odd multiples of a quarter wavelength, so the gap between successive ones is half a wavelength. Every fork should give a speed near 340 m/s, within a few percent, and the forks should agree with each other even though their wavelengths differ. A speed that is consistently low usually means the end correction at the tube mouth was ignored on a wide cylinder.
Safety
Strike the forks on the rubber mallet only, never on the bench or the glass: a struck fork against a graduated cylinder chips or shatters it. Keep water away from anything electrical and wipe up spills straight away.
Source
Adapted from OpenStax, College Physics for AP Courses Lab Manual (CC BY 4.0). Access for free at openstax.org. AP is a trademark registered by the College Board, which was not involved in and does not endorse this adaptation.
Downloads
- OpenStax Lab 12: Sound WavesPDF232 KBDownload
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