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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. This is why a large sheet of metal swung through a strong magnetic field willstop as it starts to move through the field. All of its kinetic energy will cause a major change in the

magnetic field as it enters it which will induce rings of current which will oppose the surrounding magnetic

field and slow the object down. In effect, the kinetic energy will go into driving small currents inside the

metal which will give off that energy as heat as they push through the metal.

If this isn't a satisfying answer, consider a simple wire loop being moved through a magnetic field. Ifyou've learned anything about motors and/or generators, you will have probably learned that a current will

be induced in this loop in a similar fashion. Likewise, a wire loop being pushed into a magnetic field will

induce a current which will make it difficult to continue pushing. Likewise, it will resist being pulled out as

well. An eddy current does the same thing, but instead of being forced in the path of the loop, it is allowed

to travel in the "eddy" pattern that nature provides.

To get rid of eddy currents, slits can be cut in metals so that large eddies cannot occur. This is why themetal cores of transformers are often assembled in small laminations with an insulator in between. This

prevents AC energy from being lost to eddies generated within the magnetic core (which typically is also

conductive because it is a metal like iron).

Now, sometimes eddy currents are a good thing. Mentioned above, eddy currents help turn kinetic energy

quickly into other forms of energy. Because of this, braking systems have been created which take

advantage of it. Adding a magnetic field around a spinning piece of metal will cause eddy currents in that

metal to create magnetic fields which will slow the object spinning down quickly as long as the magnetic is

strong enough.

Now, this can be taken one step farther and a circuit can be built which shuffles kinetic energy turned into

electrical energy back into a battery. This is what many Hybrid cars do (and Dean Kamen's "Segway" not

only when it is stopping but when it is going downhill).

Eddy currents are currents induced in conductors to oppose the change in flux thatgenerated them.[citation needed] It is caused when a conductoris exposed to a changing

magnetic field due to relative motion of the field source and conductor; or due to

variations of the field with time. This can cause a circulating flow ofelectrons, or acurrent, 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

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Lenz's law, causing repulsive or drag forces between the conductor and the magnet. The

stronger the applied magnetic field, or the greater the electrical conductivity of the

conductor, or the faster the field that the conductor is exposed to changes, then the greaterthe currents that are developed and the greater the opposing field.

The term eddy current comes from analogous currents seen in waterwhen dragging anoarbreadthwise: localised areas of turbulence known as eddies give rise to persistent

vortices.

Eddy currents, like all electric currents, generate heat as well as electromagnetic forces.

The heat can be harnessed forinduction heating. The electromagnetic forces can be used

for levitation, creating movement, or to give a strongbraking effect. Eddy currents can

often be minimised with thin plates, by lamination of conductors or other details ofconductor shape.

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 theresistivity 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.

Eddy currents are created when a moving conductor experiences changes in the magneticfield generated by a stationary object, as well as when a stationary conductor encounters

a varying magnetic field. Both effects are present when a conductor moves through a

varying magnetic field, as is the case at the top and bottom edges of the magnetized

region shown in the diagram. Eddy currents will be generated wherever a conductingobject experiences a change in the intensity or direction of the magnetic field at any point

within it, and not just at the boundaries.

The swirling current set up in the conductor is due to electrons experiencing a Lorentzforce that is perpendicular to their motion. Hence, they veer to their right, or left,

depending on the direction of the applied field and whether the strength of the field is

increasing or declining. The resistivity of the conductor acts to damp the amplitude of the

eddy currents, as well as straighten their paths. Lenz's law encapsulates the fact that thecurrent swirls in such a way as to create an induced magnetic field that opposes the

phenomenon that created it. In the case of a varying applied field, the induced field will

always be in the opposite direction to that applied. The same will be true when a varyingexternal field is increasing in strength. However, when a varying field is falling in

strength, the induced field will be in the same direction as that originally applied, in order

to oppose the decline.

An object or part of an object experiences steady field intensity and direction where thereis still relative motion of the field and the object (for example in the center of the field in

the diagram), or unsteady fields where the currents cannot circulate due to the geometry

of the conductor. In these situations charges collect on or within the object and thesecharges then produce static electric potentials that oppose any further current. Currents

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may be initially associated with the creation of static potentials, but these may be

transitory and small.

Eddy currents generate resistive losses that transform some forms of energy, such askinetic energy, into heat. In many devices, this Joule heating reduces efficiency of iron-

core transformersand electric motorsand other devices that use changing magneticfields. Eddy currents are minimized in these devices by selecting magnetic core materials

that have low electrical conductivity (e.g., ferrites) or by using thin sheets of magneticmaterial, known as laminations. Electrons cannot cross the insulating gap between the

laminations and so are unable to circulate on wide arcs. Charges gather at the lamination

boundaries, in a process analogous to the Hall effect, producing electric fields that opposeany further accumulation of charge and hence suppressing the eddy currents. The shorter

the distance between adjacent laminations (i.e., the greater the number of laminations per

unit area, perpendicular to the applied field), the greater the suppression of eddy currents.

The conversion of input energy to heat is not always undesirable, however, as there are

some practical applications. One is in the brakes of some trains known as eddy currentbrakes. During braking, the metal wheels are exposed to a magnetic field from an

electromagnet, generating eddy currents in the wheels. The eddy currents meet resistanceas charges flow through the metal, thus dissipating energy as heat, and this acts to slow

the wheels down. The faster the wheels are spinning, the stronger the effect, meaning that

as the train slows the braking force is reduced, producing a smooth stopping motion.

Faraday's Law

The magnitude of the induced e.m.f is determined from Faraday's Law.Faraday's Law

states that the magnitude of the induced e.m.f is directly proportional to the rate ofchange of magnetic flux through a coil or alternatively the rate of the magnetic flux beingcut.

Lenz's Law

When a magnet is moved into and out of a coil, the induced current that flows through the

coil can be determined from Lenz's Law. Lenz's Law states that the induced current

always flows in the direction that opposes the change in magnetic flux.

Lenz's Law obeys the principle of conservation of energy. Work is done to move the

magnet against the repulsive force. This work done is converted to electric energy which

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manifests as an induced current.

For a conductor in a closed circuit moving perpendicular to a magnetic field and hencecutting its magnetic flux, the direction of the induced current is determined from

Fleming's Right-Hand Rule.

Fleming's Right-Hand Rule is used to determine the direction of the induced current that

flows from the wire when there is relative motion with respect to the magnetic field

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