electromagnetic

How an electric guitar works:
http://electronics.howstuffworks.com/question701.htm
.. supplementary:
http://users.chariot.net.au/~gmarts/guitar.htm

Regards,
IanP

try http://en.wikipedia.org/wiki/Electric_guitar
om bye

why did you ask?

I think this topic is discussed in Fundamentals of Physics by Resnick and Halliday in current and magnetism section