Eddy currents also known as called Foucault currents are induced currents present in a conductors, wherein its direction is in opposition with the change in flux that generated them. When a conductor is exposed to a magnetic field that is dynamic (changing due to relative motion), Eddy currents will be present, as circulating flow of electrons, or a current, within the body of the conductor.

 These circulating eddies of current create induced magnetic fields that oppose the change of the original magnetic field due to Lenz's law, causing repulsive or drag forces between the conductor and the magnet. 

When a conductor moves relative to the field generated by a source, electromotive forces (EMFs) can be generated around loops within the conductor. These EMFs acting on the resistivity of the material generate a current around the loop, in accordance with Faraday's law of induction.

These currents dissipate energy, and create a magnetic field that tends to oppose the changes in the field.

For more information about Eddy currents, below are useful links related to the topic.

What Is An Eddy Current?
An eddy current is the current is induced in little swirls ("eddies") on a large conductor (picture a sheet of copper). If a large conductive metal plate is moved through a magnetic field which intersects perpendicularly to the sheet, the magnetic field will induce small "rings" of current which will actually create internal magnetic fields opposing the change. Read more...

What Are Eddy Current Losses?
The cores of power transformers are generally made of soft iron or steel. Because iron and steel are good conductors; a current can be induced into the core when the core is subjected to a moving magnetic field. Thus, unless special precautions are taken, large circulating currents will be induced into the core of the transformer. These currents are called as eddy currents. Read more...

Eddy Currents Explanation Video 

Simplified High-Accuracy Calculation of Eddy-Current Losses in Round-Wire Windings
It has recently been shown that the most commonly used methods for calculating high-frequency eddy-current loss in round-wire windings can have substantial error, exceeding 60%. Previous work includes a formula based on a parametric set of finite-element analysis (FEA) simulations that gives proximityeffect loss for a large range of frequencies, using the parameters from a lookup table based on winding geometry. Read more...

Eddy Currents on Solenoids
A phenomenon caused by the rate of change in an induced magnetic field. The relative motion causes a circulating flow of electrons or current within the conductor, leading to efficiency loss. Learn more about eddy current loss in the class "Solenoids 235" below. Read more...

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