Experiment 6: speed of sound

Purpose:
The purpose of this experiment is to measure the speed of sound air by analyzing the sound going back and forth through the closed tube in one end. Students will compare the experimental value to the theoretical value to analysis the error in the experiment.

Procedure:
1. Set up the microphone to the sensor and computer.

2. Measure the length and diameter of the tube.

L = 103.5 ± 0.25 cm, d = 11.55 ± 0.025 cm

3. Set up the microphone and the tube as shown.

Making a snap sound into the tube and collect data. Try until get a wave pattern which clearly shows the initial and reflected waves.

Measure the time interval between the initial and reflected waves. T= 0.00738 - 0.00086 = 0.00652 s

Calculate the speed of sound wave in air
v = 2L/T = 2(1.035)/0.00652 = 317.5 m/s

It is important for the sound we use as brief as possible because the speed of sound is about 300m/s, and the length of the tube is only 1 meter. The time for the sound going back and forth is less than 0.1s. Therefore, the brief time can make us not collect the back and forth of many times.

Calculate the speed of sound in air at room temperature (assuming that room temperature is 20 C)
 v = 331+0.60T = 331 +0.60(20) = 343 m/s
These values do not agree.

%error = (Measure - Actual)/(Measure + Actual)/2 = (317.5 - 343)/(317.5 + 343)/2 = 7.7%

The reasons which make inaccuracies in the measurement are the uncertainty of the meter stick when we measure the length, the error of the microphone when it receives the sound and transfer to the softwave to graph. The softwave actually does not read the actual sound wave; it reads the square function of the sound wave. In addition, the error when we get the time from the graph. We could not know the accurate time when we snap the finger and the time when the sound coming back. We just assume the two highest points are when the sound going back and forth. If these errors are concerned, 7.7% error is reasonable.

Summary:
Based on the purpose of this experiment, the speed of sound is measured by experiment and calculated by theoretical. The % error between those two values is reasonable if the uncertainties and errors of the measurements are concerned. The experiment is successfully shown the speed of sound in air is around 340m/s and depends on the temperature of the surrounding.