Resonance in a Closed Tube

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Resonance in a Closed Tube
Constant Length, Changing Frequency

Review: Changing Length
First resonance point: ≈ Half of difference ( ½ Δx). Decreases as f increases. Antinode to node. xinitial ≈ ¼ λ … End correction! Distance between resonance points: Constant for same frequency. Decreases as f increases. Node to node. Δx = ½ λ

Tube Length vs. Wavelength:

Calculating Wavelength:
Δx = ½ λ λ = 2 Δx L ≈ ¼ λ λ ≈ 4 L λ ≈ 4/3 L λ ≈ 4/5 L

When resonating, net displacement of molecules is zero. Amplitude at resonance points is a relative maximum, because the sound is loudest. Constant length: Constant velocity, b/c constant T. Changing frequency & wavelength, b/c length changes.

Overtones at Constant Length:

Closed Tube Resonant Frequencies:

Frequency, Wavelength, and Speed of ANY wave, including Sound:
v = f λ Know two, find the third! Wavelength calculated as a fraction of L, or L calculated from λ. Speed calculated: v = T. Frequency: measured or calculated.

Open Tube Using the analysis of a closed tube as a guide, determine the frequencies at which an open tube of fixed length will resonate.