3C50.40 - Resonance - Electromagnetically Driven Strings

Code Number:
3C50.40
Demo Title:
Resonance - Electromagnetically Driven Strings
Condition:
Good
Principle:
Resonance in wires
Area of Study:
Acoustics
Equipment:
Fred's sonometer with mounted driving and receiving electromechanical pickups, wave generator, large amplifier, small amplifier with 70 volt output, multimeter, speaker.
Procedure:

Hook up the sonometer with the receiving pickup going to the large amplifier which is connected to the speaker.  The wave generator is run to the input of the small amplifier, with the 70 volt output going to the driving pickup.  Turn the driving amplifier up so that the meter show about 10 volts on the output.  Sweep the frequencies until you find the resonant frequency of the wire as heard through the large amp and speaker.  Once this frequency is found the driving pickup may be turned up to about 20 volts so that the entire class can hear.

References:
  • Nicholas G. Horton, Thomas R. Moore, "Modeling the Magnetic Pickup of an Electric Guitar", AJP, Vol. 77, # 2, Feb. 2009, p. 144.
  • Ronald B. Standler, "Magnetically Driven Sonometer", TPT, Vol. 10, #9, Dec. 1972, p. 533, also A Potpourri of Physics Teaching Ideas - Sound, p. 259.
  • M. Podlesak and A. R. Lee, "Demonstration of Resonances in String Instruments", AJP, Vol. 52, #5, May 1984, p. 470.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.