Measurement of the speed of sound in air using the graphic calculator

Apparatus

Cardboard or plastic tube, microphone, data logger and graphic calculator.

Arrangement

1. Close one end of the tube with e.g. packing tape.
2. Place the microphone as close to the open end as possible.
3. Attach the microphone to the CH1 input of the data logger.

4. Connect the data logger to the graphic calculator.

5. Switch on the calculator and press .

6. Select DataMate.
7. Press to reset.
8. Select SETUP.
9. Select MODE and press .
10. Select TIME GRAPH.
11. Select ADVANCED.
12. Select CHANGE TRIGGERING.
13. Select CH1 MICROPHONE.
14. Select INCREASING.
15. Enter 0.1 for the trigger threshold.
16. Enter 0 for the prestore.
17. Select OK three times to return to the main screen.

Procedure

1. Select START to enable data collection.
2. Near to the open end of the tube, either snap your fingers or gently hit two sticks together. This sharp sound triggers data collection.
3. A graph such as that shown is generated. The peaks represent the sharp sound and its reflections.
4. Move the cursor to the first peak and note its time value. In the example shown the value is .0033.
5. Move the cursor to first reflection of this peak and note its time value. Note: if the first peak is above the axis its reflection will be below the axis, and vice versa. This is because waves change phase when reflected at the open end of the tube. The value in the example shown is .0092.
6. Move the cursor to the next reflection and note its time value. The value in the example shown is .0151.

Data Manipulation and Analysis

The time interval between a peak and its reflection represents the time taken for the sound pulse to travel up and down the tube. The intervals in this example are both .0059 s.

The length of the tube is 1m, thus the distance travelled by the pulse between reflections is 2 m.

This gives a value for the speed of sound of 339 m s^-1.