Clear Science!

We talked about guitar pickups and how they work. It has to do with electromagnetic induction, which says that when there’s a change in the magnetic flux through a coil of wire a current will be induced in the wire.

The little disks under an electric guitar’s strings are magnets. Each pickup has a magnet under each of the strings. (Just for the record, there are different kinds of pickups that don’t look like this, but what we’re describing is the most common kind.) Inside the pickup, there’s a wire coil around the magnets. This wire coil is connected (after going through the tone and volume knobs) to the output socket, which you connect to the amp.

Since the strings are steel, each string becomes magnetized due to the permanent magnet under it. When you pluck the string it oscillates from its original position. Since it’s magnetized, the magnetic field through the wire coil involves both the string and the magnet, and so the string’s oscillation changes the magnetic field inside the coil. (Up above we’ve represented the magnetic field with a blue shape, rather than drawing field lines.) These changes in the magnetic flux cause electrical current to go back and forth in the wire. This signal ends up at the amp and speaker, where it becomes sound waves.

Ever wondered why you don’t have to plug in an electric guitar? It makes its own electricity. 

Pickups are the strips you see under the strings on an electric guitar. They turn the physical vibration of the strings into an electrical signal. On an acoustic guitar, you hear the sound waves created by the strings’ vibration. On an electric guitar, you hear the electrical signal after it’s been run through an amplifier and comes out of a speaker. (Although the Clear Science art director couldn’t have an amp when he was a kid, so would put his ear on the horn of the guitar and hear the sound waves traveling through the solid guitar body.)

Guitar pickups work by electromagnetic induction, so let’s talk about what that is. If you have a coil of wire (a copper coil is illustrated above), a magnet passing through the coil will induce an electromotive force (EMF) in the coil. This EMF will cause an electric current to flow. (Incidentally, this is also how electric generators work.)

This concept is called Faraday’s law of induction, discovered by Michael Faraday. The EMF is equal to the time rate of change of the magnetic flux through the coil. Magnetic flux means the amount of magnetic field per area per time. Said plainer, this means changes in the magnetic field will cause some kind of current.