Hvirvelstrømme

Hvirvelstrømme, also known as eddy currents, are electrical currents induced within a conductor by a changing magnetic field. This phenomenon is a direct consequence of Faraday's law of induction. When a conductor, such as a metal plate or wire, is exposed to a fluctuating magnetic flux, the changing magnetic field causes electrons within the conductor to move, forming circulating currents.

These hvirvelstrømme flow in closed loops within the conductor. The direction of these currents is dictated by Lenz's law, which states that the induced current will flow in a direction that opposes the change in magnetic flux that produced it. This opposition often manifests as a magnetic field that counteracts the external changing field.

The presence of hvirvelstrømme can lead to several observable effects. One significant effect is Joule heating, where the resistance of the conductor causes the hvirvelstrømme to dissipate energy as heat. This principle is utilized in applications like induction cooktops and magnetic braking systems, where controlled heating or braking is desired.

Conversely, hvirvelstrømme can also be a source of unwanted energy loss in electrical devices such as transformers and motors. In these cases, efforts are made to minimize their formation, often by using laminated cores made of thin, insulated sheets of metal. This lamination increases the electrical resistance across the core, thereby reducing the magnitude of the induced hvirvelstrømme and the associated energy losses. Hvirvelstrømme are a fundamental concept in electromagnetism with both beneficial and detrimental implications depending on the context.