Preparation: a) Read about resonance in tubes closed at one end. In particular, you should be aware of the fact that the speed of sound in a tube is NOT the same as the speed of sound in open air.
b) You should know the meaning of the term “end correction”.
2. Set up apparatus as shown below.
Use the low impedance output of the signal generator. The calibration of most signal generators is approximate.
Use a frequency meter to measure the frequencies supplied by the generator. A frequency meter is connected in the same way as a voltmeter. Cause the air column in the tube to resonate at its fundamental frequency. (If you hear a resonance, how can you be sure that it is the fundamental frequency?) Measure the length of the tube l for a range of frequencies f.
b) You should know the meaning of the term “end correction”.
2. Set up apparatus as shown below.
Use the low impedance output of the signal generator. The calibration of most signal generators is approximate.
Use a frequency meter to measure the frequencies supplied by the generator. A frequency meter is connected in the same way as a voltmeter. Cause the air column in the tube to resonate at its fundamental frequency. (If you hear a resonance, how can you be sure that it is the fundamental frequency?) Measure the length of the tube l for a range of frequencies f.
It is much easier to first set the frequency and then find the length at which
resonance occurs for that frequency than to set the length and find the
corresponding frequency.
Before starting, make a quick estimate of the frequency of resonance to
be expected using the fact that for the fundamental frequency,
the length
of the tube is approximately equal to one quarter of the wavelength of the
sound; this can save a lot of time.
If the speed of sound in the tube is v and the end-correction of the tube is
e, then
l + e = v/4 f
Plot a graph from which you can find v and e.
The end-correction is usually found to be about 0·6 r where r is the radius
of the tube. See if your result agrees with this.
