The magnetic pickup of an electric guitar uses electromagnetic induction to convert the motion of a ferromagnetic guitar string into an electrical signal. Although the magnetic pickup is often cited as an everyday application of Faraday's law, few sources mention the distortion that the pickup generates when converting string motion into an electric signal, and even fewer attempt to analyze and explain this distortion. By modeling the magnet and ferromagnetic wire as surfaces with magnetic charge, an intuitive model that accurately predicts the output of a magnetic guitar pickup can be constructed. More
importantly, this model can be understood and manipulated by students at the undergraduate level and provides an excellent learning tool due to its straightforward mathematics and intuitive algorithm. Experiments show that it predicts the change in a magnetic field due to the presence of a ferromagnetic wire with a high degree of accuracy.
Nicholas G. Horton and Thomas R. Moore, "Modeling the magnetic pickup of a guitar," Am. J. Phys. 77 (2), 144-150 (2009).
American Journal of Physics