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How does a changing magnetic field produce an electric current?

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Learn about magnetic fields and the levels of particles, atoms, crystals, and domains — magnet Magnetic fields and the levels of magnetism of particles, atoms, crystals, and domains.

A changing magnetic field produces an electric current through the process of electromagnetic induction. This phenomenon occurs when the magnetic flux linked with a circuit varies over time, which induces an electromotive force (emf) within that circuit.12

The quantitative relationship governing this process is known as Faraday’s law of induction. It states that the magnitude of the induced emf is proportional to the rate at which the magnetic flux changes. Mathematically, this is expressed as:2

$e m f = - \frac{d Φ}{d t}$

Where $Φ$ represents the magnetic flux and $t$ represents time.2

When this change occurs in a closed circuit, the induced emf drives an electric current. The direction of this current is described by Lenz's law, which dictates that the current will flow in a direction that creates a reaction opposing the change in magnetic flux that caused the induction in the first place. This principle is fundamental to the operation of essential technologies, including electric generators and transformers.34