What is Eddy currents: Definition and 70 Discussions

Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or transformer, for example, or by relative motion between a magnet and a nearby conductor. The magnitude of the current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material. When graphed, these circular currents within a piece of metal look vaguely like eddies or whirlpools in a liquid.
By Lenz's law, an eddy current creates a magnetic field that opposes the change in the magnetic field that created it, and thus eddy currents react back on the source of the magnetic field. For example, a nearby conductive surface will exert a drag force on a moving magnet that opposes its motion, due to eddy currents induced in the surface by the moving magnetic field. This effect is employed in eddy current brakes which are used to stop rotating power tools quickly when they are turned off. The current flowing through the resistance of the conductor also dissipates energy as heat in the material. Thus eddy currents are a cause of energy loss in alternating current (AC) inductors, transformers, electric motors and generators, and other AC machinery, requiring special construction such as laminated magnetic cores or ferrite cores to minimize them. Eddy currents are also used to heat objects in induction heating furnaces and equipment, and to detect cracks and flaws in metal parts using eddy-current testing instruments.

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  1. A

    I Questions about cancelation of induced EMF and minimizing eddy currents

    I recalled a drawing that was provided in an EM text. Without going in length, the basics is simple - in order to minimize eddy currents one divides up a planar surface area of a wide conductor into small separate sections. As is done in transformer core laminations for example. In the image a...
  2. B

    I Power Loss Due to An Eddy Current

    Hi there! Recently, I am studying this kind of power loss from the following link: https://www.electricalvolt.com/2019/08/eddy-current-loss-formula/?expand_article=1 Just to summarize an idea, Supposed that we got a material, which is penetrated by a magnetic flux. The material will generate...
  3. thedubdude

    I Why does metal moving though a magnetic field slow down?

    A piece of metal moving West to East in a North to South fixed magnetic field slows down...but how? Yes of course eddy currents are set up in the metal and these currents generate their own magnetic field which somehow slows down the moving metal piece...but how does this actually slow the...
  4. M

    I Inductive heating and eddy currents

    Quick question 1st, is there a Magnetics forum here on PF? I am working on a project that is inductive heating using two coils and some simplified current control circuitry that can drive coils 10-100kHz. I have some questions around the magnetic fields and localized eddy currents. Let me set...
  5. Stardust99

    I Generating eddy currents, what is the best way?

    Hello I would like to lift aluminum parts with the help of eddy currents. The bar magnets A are plugged on the drums B or C. The drums are rotating. What is the best arrangement of the magnets (B or C) to lift the aluminum? Does anyone know ? Thanks and greetings.
  6. Narayanan KR

    A Question on Skin Effect and Eddy Currents

    When you try to create time varying magnetic fields in solid metals, there is severe heating due to eddy currents, when you increase the frequency, just like in NDT(non destructive testing) the magnetic field is pushed away from the core to the periphery due to eddy currents opposing the field...
  7. P

    I An Alternative explanation for energy loss due to Eddy currents

    Explanation 1: Eddy currents induced, energy loss due to joule heating. Explanation 2: Eddy currents induced, induced magnetic dipole formed. Energy is lost as work has to be done to overcome the attractive/repulsive force due to the magnet and the induced magnetic dipole from the eddy...
  8. Einstein44

    Force of Eddy Currents

    I have jus thought about how maybe I could sue the magnetic field strength equation for a solenoid (that I used to find the Emf in the first place) again, to find the magnetic field strength arising from the induced current: B= μNI / L where μ is the permativity of free space N= Number of...
  9. Einstein44

    Eddy currents in electromagnetic train

    I know that the magnitude of the eddy currents is proportional to the magnetic field, which means it should increase as I add more magnets. However I am unsure if this approach is correct.
  10. B

    Motional EMF for loops of wire vs conducting plates

    I'm in an intro E&M class, and I'm trying to distinguish between Motional EMF for loops of wire and conducting plates. This question might be kind of silly, but are Eddy currents pretty much the same thing as induced currents in a loop of wire? More specifically, what I am trying to ask is if...
  11. iVenky

    Can light cause eddy currents?

    This may sound dumb.. We know metals reflect microwave. One way to look at this is considering an eddy current formed inside the metal that cause the reflected EM Flux. When glass reflects light, does something similar happen? Can we have eddy currents (or something analogous) with light since...
  12. K

    Eddy currents in Faraday's Law Experiment

    My explanation: A circular coil is connected to an AC supply at a frequency of 30-50 kHz (radio frequency). Therefore, an alternate current will be running through this “primary” coil, producing an alternating magnetic field. This magnetic field periodically decreases in strength, alternating...
  13. Physics lover

    Eddy current Losses due to different materials

    I know only about Laminated,Iron and wooden coil.I don't know what is Air cored coil. So according to me,it should be Wooden cored coil because less current will flow through wooden cored coil.Ans it will be maximum in Iron cored coil. Please tell,am I correct or not?I don't know the answer.
  14. R

    Eddy currents in an Aluminum substrate PCB

    Well, then: my first real topic here on PF :angel: We will soon do a half-bridge PWM thing, if everything goes smoothly. Bit of a scary thing, actually. So far it's about gathering reference material and examples. Even the simulations are just in planning phase. But: as it seems the...
  15. A

    Ansys Maxwell Simulation - Evaluation of Eddy currents in a Vessel

    Hi, guys, I am developing a simulation in Ansys Maxwell. I set up my simulation in the "transient mode", and I would like to evaluate the eddy currents that arise in a metal Vessel. The currents rise to a flat top in 20 ms and then after 20 ms in the flat top, it decreases to zero in 20 ms. I...
  16. G

    PCB traces are overheating (due to eddy currents ?)

    I’m facing strange phenomenon in voltage multiplier operation – PCB traces are overheating. Multiplier runs at 50KHz, consumes 40V / 26A and delivers 500V / 2A. The prototype is continuously monitored by IR camera due to overheating concern. None of electronic components is heating...
  17. P

    Missing eddy currents in copper?

    I have a set of little flywheels that have a magnet to break the motion of the system. I have one aluminum and several copper ones all water jet cut roughly to size. The copper and aluminum disks I have are all the same dimensions but bought from three different sources. Yesterday I machined the...
  18. P

    Medical Eddy Current Hazards: Magnetic Field & Human Body

    Suppose a 10k Gauss 3in diameter sharp magnetic field is made & collapses completely thru a standing human human body somewere made by an external electromagnet.. The electromagnet is held horizontally and not vertically against body. Is this hazardous? Can it become hazardous after some...
  19. Ron Burgundypants

    Altered inductance around a solenoid in a cryostat (from Eddy currents?)

    I'm trying to use a solenoid to measure the magnetocaloric effect of dysprosium. The effect is highest at the Neel temp which is down near 180K. I have a solenoid in a cryostat to get the correct temperature. The cryostat's heat exchanger is made of a thick copper cylinder and I think it is...
  20. Michael Sofroniou

    Braking Force from Eddy Currents on a Rotating Disk

    Hello! I'm currently working on a project that will utilize the phenomena of eddy currents to apply a braking force to a rotating disk. Some background on this project: My team was tasked to create a physical therapy training device to train patients in wheelchair propulsion at resistances lower...
  21. PainterGuy

    Eddy currents in case of synchronous and asynchronous motors

    Hi, In an AC 3-phase induction motor (i.e. asynchronous motor) rotating magnetic field is produced by the stator and in this case rotor consists of simple cage having metallic bars or with coils wound around the rotor. The rotating magnetic field magnetizes the rotor and attracts it. As the...
  22. S

    Exploring Eddy Currents & Lenz's Law

    Homework Statement In one of the most common examples of Lenz's Law a magnet is dropped inside a copper tube and due the induced emf and the eddy currents generated in the copper tube the magnet falls through it with constant velocity. The external force that the eddy currents oppose is...
  23. L

    Designing a Magnetic Brake with Eddy Currents: A Mechanical Engineering Project

    Hello there guys.I am currently doing an undergraduate degree in Mechanical Engineering and in order to graduate I have to do a major project by my choosing.So i I chose а magnetic brake, using eddy currents principle.We all saw that cool videos in youtube with magnets and copper tube.So i came...
  24. G

    Eddy current losses in microelectric generators?

    For a microscale electric generator (where the driving force is a fraction of a Newton), can losses from eddy currents be significant enough to noticeably alter the rotational velocity of the rotor? Because my understanding is that the rotation is basically taken as a constant when examining the...
  25. F

    Modelling eddy currents in a pendulum

    Hello, I was solving a problem related to Eddie currents recently and I need some help with simulating it numerically. Basically, we have a disc-like copper pendulum entering a region of uniform magnetic flux density B (see diagram). I understand that I need to use Faraday's law: \nabla...
  26. G

    Self inductance of a superconductor

    Hi. Superconductors can be made hover above or even below magnets. As far as I know, this can be interpreted as an extreme form of Lenz's law: Eddy currents on the surface of the superconductor create an opposing force that is able to cancel gravity since the currents aren't affected by...
  27. R

    Forces acting on bar magnet inside a charged solenoid

    This is not a specific homework problem. It is a lack of understanding in theory relating to a lab report I have to write. We (my group and I) wrapped a 40 cm PVC pipe in copper wire (very densely and for almost the entire length), applied a current to it, and dropped a permanent magnet...
  28. S

    Eddy Current Brake Behavior (Accelerating From Rest)

    Hey guys, So I'm interested in the application of an eddy current brake system as a high intensity shock absorber of some sort. The system would consist of permanent magnets concentrated on a stationary, non ferromagnetic metal. If a sudden, intense force were to act upon the non ferromagnetic...
  29. A

    Reduction of eddy currents' magnetic field during induction

    Since the field in the title is opposing the original magnetic flux that causes the induction, how can it be reduced? I understand that a laminated magnetic core can be used. 1) Where is this magnetic laminated core placed? 2) Can it be obtained from specialized manufacturers? 3) My choice for...
  30. V

    Why are eddy currents circular?

    i tried to fig it out by watching a lot of vid on it but no chance help me
  31. L

    Type of resistance imposed by eddy currents in inductors?

    I've got a rather simple inquiry, but I haven't been able to get a straight answer via Google searches. When evaluating the impedance of an inductor, do eddy currents represent a series resistance through, or a parallel resistance around the ideal inductor? I've read that eddy currents are...
  32. J

    Transformers & Eddy Currents

    Hi pf, Could someone please explain to me why the back emf on the primary caused by eddy currents does not result in power loss. From what I have been reading about transformers eddy currents have two effects: 1) Producing heat (P=I^2R) 2) Producing a flux which opposes the primary flux I am...
  33. Sam19KY

    Question about eddy currents ?

    If a magnet is being moved in a conducting coil, are eddy currents produced in that coil ? And why ? I think the answer is yes bcz a changing magnetic field creates eddy currents in a conductor (whether it was a coil or not) . Correct me if i am wrong . Thanks !
  34. L

    Will a Magnet and Copper Tube Hourglass Be Accurate Due to Lenz's Law?

    I had the idea of making an hourglass timepiece employing lenz's law using a magnet and copper tube (or copper bars for visibility). Any idea how accurate my hourglass will be? I know Lenz's law is effected by temperature (not sure by how much). If I drop a small magnet drop through a small...
  35. L

    What are the effects of eddy currents in an inductor core?

    I've been googling around, and I can't seem to find a straight answer to this: Do eddy currents generated within an inductor core change the inductance, the impedance, or both? My reason for asking is to understand whether more or less eddy currents will change the resonant peak of the...
  36. D

    Asking a question about eddy currents

    Hi All, I am new to this forum. Thanks for viewing my question in advance. I have a confusion about the duration of eddy current. All the formulae I found are to calculate the intensity of the current. I am implementing a switch in my experiment which will turn on/off the magnetic field inside...
  37. PhiowPhi

    Eddy currents, and induced current, can they both co-exist?

    Im a bit confused about one point. Can Eddy current, and induced current exist at the same time...? If a conductor is a part of a closed circuit, and there is a change in magnetic flux over time, both Eddy current and induced current would oppose that change? Let's assume a conductor that is a...
  38. M

    Eddy currents and Torsion Pedulum

    I am having difficulties writing my damped oscillations lab report. We were asked to write a short essay on eddy currents (creation,direction advantage and disadvantage) and their relationship with torsion pendulums. Also,we have to explain if the copper wheel in the torsion pendulum could be...
  39. S

    Inductance proximity sensor

    Hi To detect position of a metal we can use the eddy currents induced by a current carrying inductor. It is described in this link. http://www.marktec.co.jp/e/product/ndt/ect/principle.html [Broken]Would this still work if the target is a magnet enclosed in a metal casing. Basically I need to...
  40. P

    Eddy Currents and Lenz's Law

    A metallic disc attached to a rod swings between two opposite magnetic poles, and its oscillation dies away very quickly. I thought this happens because the eddy currents formed inside the disc are established in a direction that would cause their magnetic field to oppose the magnetic field...
  41. K

    Current drawn from motors and Eddy Currents

    Hi, I am about to sit my Physics A-level paper next week and I have a couple of questions. My first question is rather broad, but what are eddy currents? I understand they're formed in transformers and how their effect is reduced, but I don't understand exactly why they're caused. Am I right...
  42. P

    Understanding the Fundamentals of Eddy Currents: Explained Simply

    hi all. I understand wikipaedias explination of eddy currents but could someone please explain more fundamentaly how they work. Thanks in advance :)
  43. T

    How Eddy Currents Produce Attractive Electromagnetic Forces-Maglev

    How Eddy Currents Produce Attractive Electromagnetic Forces--Maglev Hello, I am working on a paper about maglev systems and am trying to describe attractive electromagnetic suspension systems, but I am having a little trouble exactly visualizing how this works, which from what I have read is...
  44. S

    Eddy currents for measurement of twist angles

    hey, could someone tell me if it is possible to measure the angle of twist of a rigid shaft subjected to a torsional moment at one end by using eddy current testing?
  45. O

    Investigating magnetic field intensity of eddy currents

    How would I calculate the magnetic flux density of the magnetic field generated by eddy currents induced in a circular plate? I decided it would be reasonable to approximate this by considering the flux density of a current loop. However, it is my understanding that eddy currents are induced...
  46. O

    How to calculate power loss due to eddy currents

    Homework Statement What equation do i use to calculate the power loss due to eddy currents? I can't find an equation anywhere online.
  47. F

    Retarding force of eddy currents in a disc

    Homework Statement How to calculate braking force generated by eddy currents. If there is a disc of radius r with conductivity K, with a magnet located at a distance r-d from the center of the disc with a magnetic field B, what is the retarding force of the magnetic field created by the eddy...
  48. T

    Why do eddy currents flow the opposite direction to the right-hand-screw-rule?

    I've noticed in demonstrations that when you've got a magnetic field going through an iron core, say coming out of the page at you, that the eddy currents circulating perpendicular to them will flow clock-wise. But if you had a wire loop and put a current through it clockwise that it would...
  49. B

    Can Magnetic Fields Heat Metal & Create Eddy Currents?

    let's say we have a square piece of metal and we put this piece in a variable magnetic field, would it get heated? is this the idea of a current? If we have a rotating metal disk (as the case of a saw for instance), and the we put this rotating disk in a constant uniform magnetic field such...
  50. W

    Eddy currents and current induction questions

    Homework Statement A solenoid is connected to a power supply and a ring of metal is sitting on top of the solenoid. When the power supply is turned on the ring jumps up off the solenoid. a) Suppose that when you look down at the solenoid from above. The current due to the power supply is...