What are eddy currents?

Electricity surrounds us not only in production, but also in everyday life. A person may not even know what vortex currents are, but with the work they do, they face daily. For example, people have long been accustomed to turning on the light by simply pressing the button of the switch, without thinking about the processes taking place in this process. And it happened in this case. Therefore, in order to understand what is hidden under the term "Foucault eddy currents" and to determine the mechanism of their origin, it is necessary to recall the properties of the electric current. But first we will answer the question "why Foucault"?

The vortex currents were first mentioned in the works of the French physicist Arago DF. He drew attention to the strange behavior of the copper disk, above which was a rotating magnetized arrow. For no apparent reason, the disc began to rotate with the rotation of the arrow. At that time (1824), such behavior could not be explained, therefore the phenomenon was called "Arago phenomenon". A few years later another scientist, M. Faraday, having applied the phenomenon of electromagnetic induction to the phenomenon of Arago , came to the conclusion that in this case the movement of a disk is easy to explain from the point of view of the law mentioned. According to the proposed explanation, a rotating magnetic field acts on the atoms of the conductor (copper disk) and causes the appearance of directed motion of charged (polarized) particles in the structure. One of the properties of electric current is that there is always a magnetic field around the conductor. It is not difficult to guess that eddy currents also create their own field, which interacts with the ground, generating them. The word "vortex" characterizes the way of propagation of such currents in the conductor: their directions are looped. Based on the work of Arago and Faraday, the physics of Foucault seriously studied eddy currents. Hence the name received.

These currents differ little from the induction ones generated by the generators. If there is a vortex magnetic field (alternating, rotating) and a nearby conductor, then currents are induced in it by the action of electromagnetic fields. The larger and more massive the conductor, the higher the effective value of the currents that are created. And, eddy currents always create such a magnetic field, which resists the change in flow. As the current-root cause increases, the EMF directed oppositely, and when decreasing, on the contrary, the field of eddy currents maintains the main current. The foregoing follows from the Lenz law.

Unequivocally, it can not be said whether vortex 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, the properties of such currents themselves are in demand. Every curious boy once parceled the discarded transformer. The core (the base on which windings are wound) is always not made solid, but is recruited from a large number of thin plates of electrical steel (it is called sham). All components of the construction of the plate are covered with an insulating lacquer and baked for a reliable connection. Sometimes the core is further tightened by an isolated hairpin. This complication of the design is compulsory: it is necessary to substantially reduce eddy currents in the core. After all, as has been said, the less massive the conductor, the greater the resistance to the electric current it has.

In other cases, certain properties of eddy currents are in demand. For example, the work of induction steelmaking furnaces is based on heating a massive conductor of the action of eddy currents induced by a special generator. In addition, they are used to determine the presence of imperceptible defects in the structure of the metal.