Friday 12/4 .
Read Ohanian Chapter 17.0-17.3. You have time at the session for exercises 42,40 and 51. Secondly:
Experimental exercise 5. Measurement of the acoustic
impedance of an air column.
The Report should contain:
1. Measure the electric impedance of the loudspeaker acoustically loaded by a tube of lentgh 1m . Measure both with and without a plug in the other end of the tube. Measure up until a frequency of 1 kHz. Plot the real- and imaginary part of Zelectric versus frequency.
2. Use the model of the loudspeaker and the parameters of exercise 4 to calculate the acoustic impedance Zacoustic as a function of frequency. Plot it.
3. Explain that the resonance frequencies are given by Zacoustic becoming infinite (in practice large), and determine these frequencies both of the closed and open tube.
4. Find now the velocity of sound in air by these results.
5. The velocity of sound is theoretically given by v=(??)-½, where ? is the density and ? the compressibility. For isothermal changes of state we have that pV is constant. For adiabatic changes of state we rather have pVγ is constant (where ?=1.4 in the case of air). Can you judge whether air propagates isothermally or adiabaticly.