Electric Guitar Pickups
During the 1930’s and 1940’s, the increased popularity in jazz music created a need for an amplified guitar. While acoustic guitars rely on resonance from the oscillations of the guitar strings in the hollow body of the guitar, electric guitars are solid and do not have body resonance. Rather, when the metal strings of an electric guitar are plucked, the oscillations are sensed by electric “pickups" that transfer corresponding signals to an amplifier and speakers.
A pickup comprises of a small magnet with a coil wrapped around it, which is connected to an amplifier. The magnetic field of the magnet induces a magnetic field in the portion of the metal guitar string directly above the pickup, producing a north pole on the side of the string farther away from the pickup, and a south pole on the side closer to the pickup. (Refer to the image below for visual clarification). Therefore, when the string is plucked and oscillates, the magnetic field of that portion of the string induces a current in the coil. The induced current in the coil changes in direction in correspondence to the change in frequency of the oscillations of the metal string. The induced current transmits the frequency of the oscillations to the amplifier, which are then transmitted to the speakers.
The Fender Stratocaster guitar has three sets of pickups, located at the end of the strings on the main body of the guitar. The closer a set is to the end of the strings, the better it is able to detect oscillations with higher frequencies. However, the farther a set is to the end of the stings, the better it is at detecting oscillations with lower frequencies. To define the tone of music they want to play, guitarists play with certain sets of pickups.
To add a special touch to his music, Jimi Hendrix on several occasions wrapped the wire of the pickup coil to his own likings, altering the number of coils around the magnet. As a result, he changed the way an emf could be induced in the coil, and thus the amount by which the coils reacted to the oscillations of the metal strings.