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Code Number: 3C50.40
Demo Title: Resonance - Electromagnetically Driven Strings
Condition: Good
Principle: Resonance in wires
Area of Study: Oscillations & 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.