Pyörimisvirrat

Pyörimisvirrat, also known as eddy currents, are electrical currents induced within conductors by a changing magnetic field. This phenomenon, first described by François Arago and later investigated by Léon Foucault, occurs when a conductor is placed in a time-varying magnetic flux. According to Faraday's law of induction, a change in magnetic flux through a surface induces an electromotive force, which in turn drives a current if the surface is part of a closed circuit.

In the case of eddy currents, the conductor itself acts as the closed circuit. The induced currents flow in localized loops within the conductor, often resembling eddies in a fluid, hence the name. The magnitude of these currents depends on the strength of the magnetic field, the rate of change of the field, the conductivity of the material, and the geometry of the conductor.

Eddy currents can have both beneficial and detrimental effects. In some applications, they are intentionally used. For example, eddy current brakes utilize the resistive heating caused by induced currents to slow down moving objects without physical contact. Magnetic induction cooktops also employ eddy currents to heat cookware directly. However, in many electrical devices, such as transformers and electric motors, eddy currents are undesirable as they dissipate energy as heat, leading to inefficiencies and potential overheating. To minimize these losses, core materials in such devices are often laminated, meaning they are made of thin, insulated sheets. This increases the electrical resistance across the core and significantly reduces the magnitude of the eddy currents.