3D40.25 - Regenerative Feedback
Connect the pickup to the microphone input of the amplifier and the speaker to the speaker output.
Pluck the string of the sonometer and turn up the amplifier until you start to get "regenerative feedback". That is the string vibrations will be detected by the electromagnetic pickup, amplified by the amplifier, which will drive the speaker, whose vibrations will now in turn drive the string, and so on, and so on.
Ronald B. Standler, "Magnetically Driven Sonometer", TPT, Vol. 10, #9, Dec. 1972, p. 533, also A Potpourri of Physics Teaching Ideas - Sound, p. 259.
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