A moving string becomes a changing magnetic field
A magnetic pickup does not need to touch a guitar string to detect it. Its magnet makes a nearby steel or nickel string slightly magnetic. When the string moves, it changes the magnetic field passing through a coil of fine copper wire wrapped around the pickup. That changing field produces a tiny voltage in the coil—a process called electromagnetic induction.
The pickup therefore turns the string’s motion into an electrical pattern that follows its vibration. It is not recording sound in the air; it is sensing the movement of the string itself.
Where the pickup sits shapes the tone
A vibrating string does not move equally at every point. Near the bridge, its motion is relatively small, while farther toward the neck it swings more widely. A pickup samples the string at its own location, so pickups in different positions capture different balances of the vibration’s components, or harmonics. Bridge pickups tend to produce a tighter, brighter signal; neck pickups often sound fuller.
That electrical signal is weak, so the amplifier raises its strength enough to drive a speaker, which moves air and makes the sound audible. The guitar’s tone controls and amplifier can then reshape the signal. A small magnetic sensor thus captures not just that a note was played, but details of how and where the string moved.
