Oscillations and Waves > Instruments > Strings DCS# 0
NORMAL MODES OF STRETCHED GUITAR STRING

APPARATUS
guitar 202-05-C
HP function generator 202-08-G
amplifier
 202-09-B
big magnetron magnet 202-20-C
wireless microphone
 201A
broomstick, lab jack, foam rubber, wood blocks, etc. 202-01, 03
DESCRIPTION
Put AC current through selected guitar string.  When frequency matches normal mode frequency, string is driven to large amplitude and is audible.
a)  Find that mode frequencies occur in harmonic series.

b)  Attach small piece of solder to center of string:  lower frequencies of odd modes.

c)  Remove wire wrapping from finger board half of one string to obtain system of the two different strins joined at center.  Can find mode frequencies and see vibration pattern for each mode.  When plucked, sound is ridiculous.
-WBR
NOTES
Use the A (fifth) string.

Amplitude of applied voltage ≤ 2 V.

Support magnet on broomstick 1/2" above strings.  Place wood blocks on cloth on the guitar body below the magnet to protect the guitar.

Use foam rubber pads under guitar body and neck.