Courses: P1, P3, P13, P15, P82.01
A loudspeaker drives one end of an elastic string, while the other end goes over a pulley and hangs off the end of the bench, with a small weight (200g will do, depending on the length of the string). By varying the frequency of the function generator, which is driving the speaker, the wave will vibrate on the fundamental, the 1st harmonic, the 2nd harmonic, and so on. It is possible to place a driver at each end of the string and drive it with two frequencies slightly off from each other in order to display beats. One can use a strobe to assist in seeing these demos, but it really is not needed and it adds complexity to the presentation.
Setup: Stretch a rope across the bench behind the string, and use it to hold a black cloth. The contrast of black background and white string makes it much easier to see. Use one of the older function generators, since they retain their settings when turned off and are much simpler and more intuitive for a presenter to use, compared to the new ones. Among other things, the new ones default to 1 KHz when switched off and back on. This demo operates around 6 or 12 Hz for the fundamental. To mount the driver on a lab stand, there is a very short (less than one inch) rod in the drawer of rods in cabinet 6.
AKA: Vibrating String, nodes, anti-nodes.
