Column of Air Resonance and the Velocity of Sound
This activity uses the resonance of a column of air to measure the velocity of sound.
Glass Resonance Tube (Uniform Inside Diameter, With Scale Markings) Rubber Tube Reservoir Stand Low Frequency Generator (or Tuning Fork) Audio Measurement Setup (EA-200, graphic scientific calculator, data communication cable) Temperature Measurement Setup (EA-200, graphic scientific calculator, data communication cable, temperature probe)
Resonance is what occurs when one object vibrating at the same natural frequency of a second object causes the second object to vibrate. If you have two tuning forks of the same natural frequency located near each other and strike one of the tuning forks so begins vibrating, the other tuning fork will also vibrate even if you do not strike it. This is due to resonance. This activity uses a fixed-frequency sound source to produce resonance in a vertical resonance tube. The sound produced by the resonating column of air will sound louder than the sound produced by the sound source. The expressions below show the relationships between the length of the column of air and wavelength, and the velocity of sound and wavelength. The relationship between the velocity of sound and wavelength is called the basic equation.
í Setting Up
u Set up the equipment as shown in the illustration, and fill with water, taking care it does not overflow. u Raise and lower the reservoir and check to make sure that the level of the water changes. 1 Glass Resonance Tube 2 Tube Length: 1 meter 3 Stand 4 Reservoir 5 Rubber Tube 6 Low Frequency Generator:
Ln = 2n–1 λ – L v = f λ 4
L n(m) : Air Column Length for Resonance Point n (n = 1, 2, 3...) L (m) : Air Column Open-end Correction λ (m) : Wavelength of Sound v(m/s) : Velocity of Sound f(Hz) : Frequency of Sound Wave 1 Resonance Point 1 2 Resonance Point 2
7 Speaker 8 EA-200