Experiment 6: Speed of Sound

9/13/2012

The purpose of this experiment is measuring the speed of sound waves which are reflected back from the closed end of the tube.We measure the time for the waves to go down to the end of the tube and comeback again.

Apparatus: Logger Pro software, microphone, LabPro, computer, long hollow tube closed at one end, two-meter meterstick.

First, we measure the inside length of the tube which is 1.30+/-0.01m, then assemble the equipment. Put the microphone close to the end of the open tube. Before we make a snap by two fingers, we click collect on computer. In process, we did it three times. So we got three different graph for this sound and reflected sound.

Then take the average of them, which t=7.68*10^3+/-1.49*10^-4 s.

Use the formula v=s/t, which s=2L.

The speed of sound we measure is 338.5+/-9.4m/s

Then we use the speed of sound in air at room temperature T can be calculated from v=331+0.6T. As the result, we got v=331+0.6*18=341.8m/s The error between my measured value and the actual value is (341.8-338.5)/341.8=0.97%. The error is small. It is important for the sound we use to be as brief as possible because it is easy to find the time from begin to reflect and it can easy to reduce the error. For inaccuracies, i think we can't make sure the microphone standing on the same place of the edge of the tube. Secondly, i think it is not quiet in the classroom. But anyway, compare to snap, noisy cant have too much influences when we measure.Third, it is a little bit hard to find the accurate time from the graph.