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Standing Waves on a String

I love teaching standing waves! There is something about waves on a string that is fascinating and pupils are always love to see how many harmonics can be produced.
This demonstration uses a rubber cord, fixed at either end, but can also be performed using a string fastened to weights over a pulley: That version has the advantage that the tension can easily be adjusted (and measured) making it ideal for investigation work; This version tends to produce better waves (and more of them!)
In this demonstration I have used a digital signal generator which has the advantage that the frequency can easily be measured. The disadvantage is that this type of signal generator does not have an amplified output, and hence is incapable of driving the vibration generator on its own. To achieve this I have wired the output up to an amplifier (actually the amplifier part of aan analogue signal generator) just out of screen shot.