An electric guitar sounds different than an acoustic guitar chiefly because of differences in the bodies of the instruments. An acoustic guitar features a soundboard mounted on a hollow body that enables the vibration of the guitar strings to be readily heard, but electric guitars mostly have a solid body that lacks a soundboard. Instead, the electric guitar is designed to produce audible sound through the combined action of electricity and magnetism. The vibrations of the strings are converted into an electric signal via a magnetic component called the pickup, and this signal is then sent to an amplifier and speaker.
A single guitar pickup is illustrated in this tutorial. The pickup consists of a Coil of wire wound around a permanent magnet, the north pole of which faces up. For the sake of simplicity, the coil in the applet is composed of only a few turns; real guitar pickups typically consist of thousands.
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The permanent magnet serves to magnetize the guitar String above it (which, being steel, is ferromagnetic). So the string is, in essence, a magnet itself and its magnetic field is in alignment with that of the permanent magnet that magnetized it.
Explore how the pickup produces an electric signal by clicking the Pluck button, which vibrates the guitar string. You can interrupt the motion using the Pause button.
When the string is plucked, the magnetic field around it (shown in blue) moves up and down with the string itself. This moving magnetic field induces a current in the coil of the pickup. This is simple electromagnetic induction, as described by Faraday’s law. To understand this better, see our electromagnetic induction tutorial. Just as the moving bar magnet in that tutorial induces a current in the coil, so does the moving string (functioning as a magnet itself) induce a current in this tutorial. The changing magnetic flux through the coil induces an electromotive force that generates an alternating electric current through the wire of the pickup. The current rhythmically oscillates with the guitar string, as demonstrated by the red arrows. The direction of the current is determined by Lenz’s law, which states that an induced electric current will flow in such a way that it generates a magnetic field that opposes the change that generated it. This electric signal sent through the pickup coil travels through a simple circuit in the guitar that leads to an amplification/speaker system, enabling the signal to be heard as music. By experimenting with how the string is plucked and volume and amplifier position, electric guitarists can achieve effects such as distortion and feedback.