Experiment to measure the speed of sound in a resonance tube



Name: ________________________

Partner:

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Purpose: to measure the speed of sound in air within a resonance tube

1. Preparation: The tube you will use will be open at one end, where you will place a resonating tuning fork. The other end will be closed, sealed off by water in the tube.

a) Notice how you will always get a node at the closed end, because no vibration can occur there. Also, an antinode will always occur at the open end. The diagram at the right shows this well, displaying the 1st harmonic of vibration. If the tube were long enough, you could achieve higher harmonics, such as the 3rd seen below.

You will attempt to keep the tube sufficiently short, so as only to achieve the 1st Harmonic of oscillation.

b) If you achieve resonance in the 1st Harmonic, how much of a single wavelength is represented in the tube? Look at the diagram for the 1st Harmonic to determine this.

Amount of Wavelength in tube = __________

Be aware that the speed of sound in a tube is the same as the speed of sound in open air.

2. Set up apparatus as shown at left.

• Select a tuning fork and note the frequency. Sound the fork over the tube using only the mallet.

• Starting with the tube mostly submerged in water, raise it upward until you cause the air column in the tube to resonate at its 1st Harmonic.

Q: How does the starting with the tube mostly submerged ensure we get the first harmonic? __________________

• Measure the tube length, L, for a range of resonant frequencies f.

(You must use 4 or 5 different tuning forks)

Write λ in terms of tube length L: __λ=_______________

|Frequency (Hz) |Tube Length (m) |Wavelength (m) |

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• The speed of sound in the tube is v. You’ll need to plot a graph from which you can find v.

Using the equation:

rewrite the equation in the form of the equation for a line: y = mx, where m represents slope.

Let y be the frequency ( f ), and m be the velocity (v). After you rearrange the equation in the space below (showing what variable goes on which axis), bring it to your teacher for verification.

Now plot your y variable vs your x variable, so that the slope of your line gives you the velocity of sound in air. You can set you y-intercept to zero. Use Excel to make your graph.

Your SPEED OF SOUND value = _________________ m/s

WHAT TO TURN IN: 1) This Sheet 2) You graph fully labeled including the equation and r2 values 3) A Conclusion (according to the rubric) with a % error calculation.

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Open End

Closed End

= tube length

L

To fill in this column, you must refer back to your analysis of the 1st Harmonic. How much of a wavelength is contained within the length of the tube?

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y

x

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