2.0 Assumptions

1. The room is at a constant temperature of 15°C, in which the theoretical speed of sound is 340,00m/s;
2. The reflections along the surface of the tube can be considered negligible except for those occurring at the closed end of it;
3. The vibrations of the table on which the tube is resting and the background noise are negligible.
4. The diameter of the tube is small in comparison to its length.

2.1 Resonance Tube



1. Close one end of the tube, so that reflection of the sound wave is possible;
2. Fix the tube to the table, so that it does not move;
3. Connect the microphone to the computer;
4. Attach the microphone to one end of the stick, so that it is parallel to it;
5. Place the microphone inside the tube;
6. Open the “Soundcard Oscilloscope” (SO) program on the computer;
7. Open the “Frequency Generator” (FG) app on the phone;
8. Place the phone on the open end of the tube;
9. Select a theoretical resonance frequency1;
10. View the wave obtained in the SO, if it moves adjust the frequency in the FG, in order to obtain a standing wave;
11. Using the frequency obtained, move the microphone along the tube, in order to find the positions of the nodes;
12. Repeat steps 9, 10 and 11, using higher order frequencies.




1Note: opt for higher order frequencies, so that wave amplitude is greater, and it is possible to visualize more nodes inside the tube




2.2 Two Microphones



1. Fix the tube to the table, so that it does not move;
2. Connect both microphones to the computer;
3. Attach each microphone to a different end of the tube, so that they are parallel to it;
4. Open the “Soundcard Oscilloscope” (SO) program on the computer;
5. Clap two wooden blocks, producing a pulse, at one end of the tube;
6. View the pulses obtained in the SO and get the time interval between them;
7. Repeat steps 5 and 6, as many times as necessary.






2.3 Echo



1. Close one end of the tube, so that reflection of the sound wave is possible;
2. Fix the tube to the table, so that it does not move;
3. Connect the microphone to the computer;
4. Attach the microphone to the open end of the tube, so that it is parallel to it;
5. Open the “Soundcard Oscilloscope” (SO) program on the computer;
6. Clap two wooden blocks, producing a pulse, at the open end of the tube;
7. View the pulses1 obtained in the SO and get the time interval between them;
8. Repeat steps 6 and 7, as many times as necessary.




1Note: if the emitted pulse is not short enough, it will be not possible to distinguish different pulses (the sum of them will be displayed in the SO); in this case, the length of the tube must be increased