 As the circular plate moves down through a small region of constant magnetic field directed into the page, eddy currents are induced in the plate. The direction of those currents is given by Lenz's law. An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in 1851. It is caused when a moving (or changing) magnetic field intersects a conductor, or vice-versa. The relative motion causes a circulating flow of electrons, or current, within the conductor. These circulating eddies of current create electromagnets with magnetic fields that oppose the effect of the applied magnetic field (see Lenz's law). The stronger the applied magnetic field, or greater the electrical conductivity of the conductor, or greater the relative velocity of motion, the greater the currents developed and the greater the opposing field. Image File history File links Wikipedia_Eddy_Currents. ...
Lightning strikes during a night-time thunderstorm. ...
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1851 (MDCCCLI) was a common year starting on Wednesday (see link for calendar) of the Gregorian calendar (or a common year starting on Friday of the 12-day-slower Julian calendar). ...
Magnetic field lines shown by iron filings In physics, a magnetic field is a solenoidal vector field in the space surrounding moving electric charges and magnetic dipoles, such as those in electric currents and magnets. ...
In science and engineering, conductors are materials that contain movable charges of electricity. ...
e- redirects here. ...
In electricity, current refers to electric current, which is the flow of electric charge. ...
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. ...
An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. ...
Lenzs law (pronounced (IPA) ) gives the direction of the induced electromotive force (emf) and current resulting from electromagnetic induction. ...
Electrical conductivity or specific conductivity is a measure of a materials ability to conduct an electric current. ...
It is important to appreciate that eddy currents are created when a conductor moves across a varying magnetic field, 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 magnetised region shown in the diagram. Eddy currents will be present wherever the conducting object, which is moving, experiences a magnetic field, and not just at the boundaries. However, in some geometries, transient eddy currents can cause charges to collect on the extremities of the object and these charges then produce electric fields that oppose any further flow of current.
the swirling current set up in the conductor is due to electrons experiencing a Lorentz force 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 the current 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 varying external 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 applied, in order to oppose the decline. Lorentz force. ...
Lenzs law (pronounced (IPA) ) gives the direction of the induced electromotive force (emf) and current resulting from electromagnetic induction. ...
Eddy currents create losses through Joule heating. More accurately, eddy currents transform useful forms of energy, such as kinetic energy, into heat, which is generally much less useful. Hence they reduce the efficiency of many devices that use changing magnetic fields, such as iron-core transformers and electric motors. They are minimized by selecting magnetic core materials that have low electrical conductivity (eg ferrites) or by using thin sheets of magnetic material, 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 oppose any further accumulation of charge and hence suppressing the flow of eddy currents. The shorter the distance between adjacent laminations (ie the greater the number of laminations per unit area, perpendicular to the applied field), the greater the suppression of eddy currents. In electronics, and in physics more broadly, Joule heating refers to the increase in temperature of a conductor as a result of resistance to an electrical current flowing through it. ...
Figure 1:Three-phase pole-mounted step-down transformer. ...
Electric motors of various sizes. ...
A magnetic core is the core of an electromagnet or inductor. ...
Ferrites are ferromagnetic ceramic materials, compounds of iron, boron and barium or strontium or molybdenum. ...
Laminate flooring Laminated core transformer A laminate is a material constructed by uniting two or more layers of material together. ...
Hall effect diagram, showing electron flow (rather than conventional current). ...
The loss of useful energy is not always undesirable, however, as there are some practical applications. One is in the brakes of some trains known as an eddy current brake. During braking, the metal wheels are exposed to a magnetic field from an electromagnet, generating eddy currents in the wheels. The eddy currents meet resistance as they 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. Eddy current brakes at the Intamin roller coaster Goliath in Walibi World (Netherlands) Eddy current brake, like conventional friction brakes, are responsible for slowing an object, such as a roller coaster. ...
The term eddy current comes from analogous currents seen in water when dragging an oar: localised areas of turbulence known as eddies give rise to persistent vortices. Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...
An oar is an implement used for water-borne propulsion. ...
Applications
Electrical Eddy currents are used to great effect in movement-to-electricity converters such as electrical generators and dynamic microphones. They can also be used to induce a magnetic field in aluminum cans, which allows them to be separated easily from other recyclables. Superconductors allow perfect, lossless conduction, which creates eddy currents that are equal and opposite to the external magnetic field, thus allowing magnetic levitation. For the same reason, the magnetic field inside a superconducting medium will be exactly zero, regardless of the external applied field. “Dynamo†redirects here. ...
A microphone, sometimes referred to as a mike or mic (both IPA pronunciation: ), is an acoustic to electric transducer or sensor that converts sound into an electrical signal. ...
A typical can of Diet Coke. ...
Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ...
Levitating pyrolytic carbon Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended above another object with no support other than magnetic fields. ...
Mechanical Eddy currents are used for braking at the end of some roller coasters. This mechanism has no mechanical wear and produces a very precise braking force. Typically, heavy copper plates extending from the car are moved between pairs of very strong permanent magnets. Electrical resistance within the plates causes a dragging effect analogous to friction, which dissipates the kinetic energy of the car. General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Standard atomic weight 63. ...
Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...
Structural Testing Eddy current techniques are commonly used for the nondestructive examination (NDE) and condition monitoring of a large variety of metallic structures, including heat exchanger tubes, aircraft fuselage, and aircraft structural components. // Nondestructive testing (also called NDT, nondestructive evaluation, NDE, and nondestructive inspection, NDI) is testing that does not destroy the test object. ...
A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. ...
Look up Tube in Wiktionary, the free dictionary. ...
Another eddy current technique for nondestructive testing was developed by Dr. Abdollah Abtahi using the Fourier transform method in 1981. This technique allowed small flaw detection in a large area much faster than any other technique. This method predicts very accurate results for small flaws in a large area. This method can be applied for testing any flaws in an airplane body/fuselage or a large satellite dish. This research was supported with a grant by the Electric Power Research Institute (EPRI). The Electric Power Research Institute (EPRI) conducts research on issues of interest to the electric power industry in the USA. EPRI is an independent, nonprofit organization funded by the electric utility industry. ...
Side Effects Eddy currents are the root cause of the skin effect in conductors carrying AC current. The skin effect is the tendency of an alternating electric current (AC) to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core. ...
Links to Applications Adjustable speed drive (ASD) is one of the most general terms applied to equipment used to control the speed of machinery. ...
Eddy-Current testing uses electromagnetic induction to detect flaws in conductive materials, amongst other operations. ...
Typical US domestic electricity meter An electric meter or energy meter is a device that measures the amount of electrical energy supplied to a residence or business. ...
Electromagnetic brakes, also called eddy current brakes, seek to retard motion or cause deceleration in a moving system. ...
Induction Hob (Top View) An induction cooker uses induction heating for cooking. ...
It has been suggested that this article or section be merged with Inductive sensor. ...
Proximity sensors are sensors able to detect the presence of near objects without any physical contact. ...
Cigarette vending machine. ...
Speedometer gauge on a car, showing the speed of the vehicle in miles and kilometres per hour on the out– and inside respectively. ...
References - Fitzgerald, A. E.; Kingsley, Charles Jr. and Umans, Stephen D. (1983). Electric Machinery, 4th ed., Mc-Graw-Hill, Inc., page 20. ISBN 0-07-021145-0.
- Sears, Francis Weston; Zemansky, Mark W. (1955). University Physics, 2nd ed., Reading, MA: Addison-Wesley, pages 616-618.
External links - A video demonstration of Eddy currents
- The Eddy Current Loss Anomaly
- Eddy current separators for non-ferrous metals separation - these machines are used in the recycling sector for the automatic selection of the raw materials
- Videos of Eddy current separator
See Also - Eddy current testing world wide
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