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Physics 2, Lab 1

# Physics 2, Lab 1 - Physics Lab 1 Resonance Tube Joshua...

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Physics Lab 1 Resonance Tube Joshua Budhu Section: W 11-12:50 Lab Partner: Andrew Nouri Date Peformed: 2/4/09 Date Due: 2/11/09

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1 Objective: In this lab, standing sound waves are studied in regards to differing boundary conditions. At one end of the tube there is a speaker; at the other, there is an adjustable piston which is used to change the length of the tube or leave the end of the tube completely open. At the speaker end, sinusoidal waves are propagated as a small microphone in the tube reads the sound waves. We will study the resonant frequencies of the tube by determining where the sound waves are the most prominent. In the second part of the experiment, a sound pulse will be emitted, and the reflected pulse will be inspected. The characteristics of the indicated pulse will differ, depending on if the tube is opened or closed. We will also measure the speed of sound. 2 Theory: 2.1 Air as a Spring The molecules in gas are elastic in nature. In a closed off cylinder with a piston, the air pressure on both sides of the piston is the same. Pushing the piston in compresses the gas trapped inside, increasing the pressure, which in turn leads to a net force pushing the piston out. In the opposite case, with the piston being pulled out, the trapped gas can take up more space, allowing the pressure to drop, thus leading to a net force pushing the piston back in. Due to its springy nature and the fact that it has mass, gas can sustain oscillations and waves. In this experiment, we are observing air, composed of approximately 80% N 2 and 20% O 2 . 2.2 Traveling Sound Waves in Air Air next to a load speaker moving out compresses and the air molecules gain an outward velocity, combining with the thermal velocities that these molecules already possess. The air molecules from which this motion originates, nearest the speaker, collide with the neighboring air molecules and pass on this motion. The compression spreads away from the speaker, and sound is produced. The same theory applies to the opposing case when the speaker is moved inward. If the speaker is vibrated sinusoidally, a
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