Electricity surrounds us not only in production, but also in everyday life. A person may not even know what eddy currents are, but face the work they do every day. For example, people have long been accustomed to turning on the light by simply pressing the switch button, without thinking about the processes that occur during this. And so it happened in this case. Therefore, in order to understand what is hiding under the term “Foucault eddy currents” and determine the mechanism of their occurrence, it is necessary to recall the properties of the electric current. But first, the answer to the question "why Foucault?"
For the first time eddy currents were mentioned in the works of the French physicist Arago D.F. He drew attention to the strange behavior of a copper disk, above which a rotating magnetized arrow was located. For no apparent reason, the disk began to rotate along with the rotation of the arrow. At that time (1824) they could not explain such behavior, therefore the phenomenon was called the “Arago phenomenon”. A few years later, another scientist - M. Faraday, applying the law of electromagnetic induction he discovered to the Arago phenomenon , came to the conclusion that in this case the movement of the disk is easy to explain from the point of view of the mentioned law. According to the proposed explanation, a rotating magnetic field acts on the atoms of the conductor (copper disk) and causes the directional movement of charged (polarized) particles in the structure. One of the properties of electric current is that there always exists a magnetic field around a conductor. It is easy to guess that eddy currents also create their own field, which interacts with the main one that generates them. The word "eddy" characterizes the distribution of such currents in the conductor: their directions are looped. Based on the work of Arago and Faraday, the physicist Foucault studied seriously eddy currents. Hence the name obtained.
These currents are not much different from induction generated by generators. If there is a vortex magnetic field (alternating, rotating) and a conductor located nearby, then currents are induced in it due to the action of electromagnetic fields. The larger and more massive the conductor, the higher the effective value of the created currents. Moreover, eddy currents always create such a magnetic field that resists the change in flow. With an increase in the root cause current, the counter-emf directional increases, and with a decrease, on the contrary, the eddy current field maintains the main flow. The foregoing follows from the law of Lenz.
It is definitely impossible to say whether eddy currents are useful or harmful: in some cases they are regarded as parasitic and various technological solutions are used to reduce them, while in others, on the contrary, the properties of such currents themselves are in demand. Each curious boy once dismantled a discarded transformer. The core (the base on which the winding coils are wound) is always made not whole, but is drawn from a large number of thin plates of electrical steel (it is called burdened). All components of the structure are coated with an insulating varnish and baked for a reliable connection. Sometimes the core is further pulled together by an insulated stud. Such a complication of the design is necessary: it is necessary to significantly reduce eddy currents in the core. After all, as already mentioned, the less massive the conductor, the greater its resistance to electric current.
In other cases, some properties of eddy currents are in demand. For example, the operation of induction steelmaking furnaces is based on the action of eddy currents induced by a special generator heating a massive conductor. In addition, they are used to determine the presence of imperceptible defects in the metal structure.