An eddy current is a looping electric current that forms inside a metal when it experiences a changing magnetic field.

Simple definition

  • When a magnetic field through a conductor changes (or the conductor moves through a magnetic field), charges inside the metal start circulating in closed loops. These loops are called eddy currents.
  • They arise from electromagnetic induction, described by Faraday’s law and Lenz’s law, which say induced currents always oppose the change that created them.

How eddy currents behave

  • Eddy currents flow in closed loops within the bulk of the conductor, in planes roughly perpendicular to the magnetic field.
  • Because real materials have resistance, these circulating currents generate heat and can produce mechanical forces (push, pull, or braking effects) on the conductor.

Everyday examples

  • Induction cooktops and industrial induction heaters use strong eddy currents in metal to generate heat for cooking or forging.
  • Electromagnetic brakes in some trains and roller coasters use eddy currents in metal fins passing between magnets to create a smooth braking force without contact.
  • Transformers and electric machines try to reduce unwanted eddy currents in their iron cores because they waste energy as heat, so the cores are laminated into thin sheets.

Quick physics view

  • Cause: changing magnetic flux through a conductor (either the field changes with time, or the conductor moves through the field).
  • Effect: circulating currents create their own magnetic field that opposes the original change (Lenz’s law), which can slow motion, generate heat, or distort the magnetic field.

TL;DR: An eddy current is a swirling induced current inside a conductor caused by a changing magnetic field, which can either be useful (heating, braking, testing) or a loss (wasted heat in transformers).