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Eddy current testing (ECT) as a technique for testing finds its roots in electromagnetism. Eddy currents were first observed by François Arago in 1824, but French physicist Léon Foucault is credited with discovering them in 1855. ECT began largely as a result of the English scientist Michael Faraday's discovery of electromagnetic induction in
The Maxwell–Faraday equation (listed as one of Maxwell's equations) describes the fact that a spatially varying (and also possibly time-varying, depending on how a magnetic field varies in time) electric field always accompanies a time-varying magnetic field, while Faraday's law states that emf (electromagnetic work done on a unit charge when ...
A diagram of Faraday's iron ring apparatus. Change in the magnetic flux of the left coil induces a current in the right coil. [2] Electromagnetic induction was discovered by Michael Faraday, published in 1831. [3] [4] It was discovered independently by Joseph Henry in 1832. [5] [6]
A diagram of Faraday's iron ring-coil apparatus Built in 1831, the Faraday disc was the first electric generator. The horseshoe-shaped magnet (A) created a magnetic field through the disc (D) . When the disc was turned, this induced an electric current radially outward from the centre toward the rim.
The discovery of electromagnetic induction was made almost simultaneously, although independently, by Michael Faraday, who was first to make the discovery in 1831, and Joseph Henry in 1832. [77] [78] Henry's discovery of self-induction and his work on spiral conductors using a copper coil were made public in 1835, just before those of Faraday.
Eddy currents in conductors of non-zero resistivity generate heat as well as electromagnetic forces. The heat can be used for induction heating. The electromagnetic forces can be used for levitation, creating movement, or to give a strong braking effect. Eddy currents can also have undesirable effects, for instance power loss in transformers.
Michael Faraday developed the concept of lines of force to describe electric and magnetic phenomena. [13] In 1831, he writes [ 13 ] By magnetic curves, I mean the lines of magnetic forces, however modified by the juxtaposition of poles, which would be depicted by iron filings; or those to ·which a very small magnetic needle would form a tangent."
Electromagnetic induction was first described by Michael Faraday in 1831. [8] [9] In Faraday's experiment, he wrapped two wires around opposite sides of an iron ring. He expected that, when current started to flow in one wire, a sort of wave would travel through the ring and cause some electrical effect on the opposite side.