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Unformatted text preview: 1 1 Name ________________ Partner _______________ Physics 198 Laboratory #3 : STANDING WAVES IN A TUBE OBJECT : To study the relationship between the speed of sound and the nodes and antinodes of both open/open and open/closed tubes. THEORY : A traveling wave from outside enters a tube is reflected at the far end. The reflected wave is inverted if the end of the tube is open, otherwise it is not inverted. If the wavelength is just right a natural resonant frequency of the tube is excited. This occurs when the frequencies are as follows. f n = n ( v 2 L ) with n = 1,2,3,4,5,... for an open/open tube, n is the number of half wavelengths inside the tube, i.e., all harmonics are present. f n = n ( v 4 L ) with n = 1,3,5,7,9... for an open/closed tube, n is the number of quarter wavelengths inside the tube , only odd harmonics are present. By measuring f n , n , L , we can find the speed of sound, v . This can be compared with the expected value: v = 331.5 + 0.6 T in meters/second with T in degrees C. EQUIPMENT : The major equipment include a hollow glass tube with microphone probe, a function generator driving a small speaker, an oscilloscope and an audio amplifier with headphones. There should also be a digital thermometer and a caliper for measuring tube diameter. See diagram directly below and picture a bit further down. 2 2 DESCRIPTION : A small speaker is driven by a function generator. By changing the settings, the amplitude and frequency of the electronic signal can be varied. Please leave the function generator set on sine for this lab. (You can, of course, play with any settings if you like, just return to the standard positions before taking data.) A small microphone and preamp detects small changes in pressure. These are powered by a battery. The signal from the microphone is filtered and amplified and displayed visually on an oscilloscope and can also be heard with earphones. The volume control on the amplifier affects the headphones signal, but not the signal to the oscilloscope. Be sure to keep the volume at a reasonable level. If you have trouble with the equipment, please ask the instructor for help. equipment, please ask the instructor for help....
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- Fall '09