Hvirvelstrømmer

Hvirvelstrømmer, also known as eddy currents, are electrical currents induced within a conductor by a changing magnetic field. This phenomenon was first described by physicist Léon Foucault in 1851. When a conductor, such as a piece of metal, is placed in a region where the magnetic flux through it is changing, an electromotive force (EMF) is generated according to Faraday's law of induction. This EMF, in turn, drives currents within the conductor.

These induced currents flow in closed loops, resembling eddies in a fluid, hence the name hvirvelstrømmer. The direction of these currents is such that they oppose the change in magnetic flux that produced them, as described by Lenz's law. This opposition means that hvirvelstrømmer can lead to a braking effect, as seen in magnetic brakes used in trains and roller coasters.

Hvirvelstrømmer also generate heat due to the electrical resistance of the conductor. This heating effect is utilized in induction cooktops and industrial heating processes. However, hvirvelstrømmer can also be undesirable, leading to energy losses in electrical machinery like transformers and motors. To minimize these losses, the conductive cores of such devices are often made of thin laminations insulated from each other, which increases the resistance to the flow of hvirvelstrømmer. The study and application of hvirvelstrømmer are important in various fields of electrical engineering and physics.