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Physics · Waves · Resonance
Speed of sound by resonance tube
A vertical tube is partly filled with water; a vibrating tuning fork is held above the open top. The water level is adjusted until the column of air sings strongly — that is the first resonance position. The second resonance occurs three times deeper. From L₁ and L₂, the speed of sound can be calculated.
air column length (drag water level)
L = 50.0 cm
Results · v = fλ, λ = 2(L₂−L₁)
| Fork | L₁ (cm) | L₂ (cm) | λ (cm) | v (m/s) |
|---|---|---|---|---|
| 256 Hz | — | — | — | — |
| 384 Hz | — | — | — | — |
| 512 Hz | — | — | — | — |
Exam-style questions
1. At the FIRST resonance, what fraction of a wavelength is in the air column?
2. Using L₁ and L₂, how do you calculate λ?
3. Why use BOTH L₁ and L₂ rather than just L₁?
4. If 384 Hz resonates at L₁ = 22.0 cm and L₂ = 67.0 cm, speed of sound?