Virvelströms

Virvelströms, also known as eddy currents, are circular currents of electrical conductivity that are induced in a conductor when it is exposed to a changing magnetic field. This phenomenon was first described by François Arago in 1824 and later explained by Léon Foucault in 1851, leading to the term "eddy currents" sometimes being referred to as Foucault currents.

Eddy currents are generated according to Faraday's law of induction. When a magnetic field through a conductive material changes, a voltage is induced, which in turn drives a current. Because the conductor is a continuous material, these induced currents flow in closed loops, much like eddies in a fluid. The direction of these currents opposes the change in magnetic flux that caused them, as described by Lenz's Law.

The presence of eddy currents can have both beneficial and detrimental effects. In some applications, they are intentionally generated. For example, induction heating uses eddy currents to heat conductive materials rapidly. Magnetic braking systems in trains and roller coasters also utilize eddy currents to slow down moving vehicles by generating opposing magnetic forces. Eddy current testing is a non-destructive method used to detect surface and near-surface flaws in conductive materials.

However, eddy currents can also be a source of energy loss and heat generation in electrical devices like transformers and electric motors. The induced currents flow through the resistance of the conductive material, dissipating energy as heat (Joule heating). To minimize these losses, materials like laminated cores are used in transformers. Lamination involves stacking thin, insulated sheets of metal, which break up the paths of eddy currents, significantly reducing their magnitude and the associated energy loss.