# What is Currents: Definition and 496 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.

View More On Wikipedia.org
1. ### Phase currents of Trapezoidal switching

For trapezoidal switching or 180 degree switching these are the waveforms when i referred to the website 180 switching when i calculated the RMS value of the phase voltage it is Vp = 0.4714Vs so assuming the Vs = supply voltage = 20V and each phase - phase resistance as per the data sheet is...
2. ### Symmetrical parallel inductors, different currents? State Preparation

We have there parallel inductors (i.e. having the same voltage) with the same inductance, having different currents at a particular time. It appears that this is only possible if the current phasors have different phases See bottom left of video below, ##I_1, I_2, I_3## (time already set to...
3. ### I Noether currents for a complex scalar field and a Fermion field

For a complex scalar field, the lagrangian density and the associated conserved current are given by: $$\mathcal{L} = \partial^\mu \psi^\dagger \partial_\mu \psi -m^2 \psi^\dagger \psi$$ $$J^{\mu} = i \left[ (\partial^\mu \psi^\dagger ) \psi - (\partial^\mu \psi ) \psi^\dagger \right]$$...
4. ### B The historical war of currents in Mains Power Distribution: AC vs DC

So, if I get it right, the basic argument goes like this: AC was preferred to DC because its voltage can be stepped up by a transformer. This limits losses while the current is transported from the production plant to the final user. The voltage is subsequently stepped down when delivered to the...
5. ### Help with finding mesh currents and nodal analysis

Hi there, I have managed to work out the kirchoff's law bit but for the other two bits I just cant get started as I can get my head around it, its due in on monday I dont know why I left it so late!
6. ### I Can Superconductors Reach Relativistic Speeds and Emit Synchrotron Photons?

How are currents injected into a superconductor? And can you regulate the velocity of the current afterwards? Since the magnetic field can’t penetrate? What would happen if you tried to make the Cooper pairs approach relativistic speeds? Would the superconductor stop being in its...
7. ### Spikes in LTspice voltages and currents

Attached is a screenshot of an amp I am running in Ltspice. There are spikes on all the currents and voltages displayed, can anybody tell me why?
8. ### I Molten metal flow due to high currents

It is mentioned in the book "Ampere-Neumann Electrodynamics of Metals", Peter Graneau, that Carl Hering in 1923 operated furnaces by passing high current through the molten metal pool. He observed molten metal flow due to the currents. How is the conductor motion explained?
9. ### I Coulomb's law for steady currents

If I've steady currents i.e ##\frac{\partial}{\partial t} J=0## , does coulombs law hold in this case to find the electric field? Since this isn't the case of electrostatics so it might not hold, but if we look at the charge density it is the same for all time, this suggests that the charges...
10. ### 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...
11. ### 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.
12. ### B Birkeland Currents Collision: Effects & Consequences

What would happen if two birkeland currents collided?

14. ### Engineering Is my answer correct? (Mesh Currents)

Hello I am solving the following circuit bellow on the homework statement terms I will leave also my resolution as a png And appologise in advance i my writing is hard to read My solution: Can you tell me if I am on the right track or help me get there? Your help time and attention are...
15. ### 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...
16. ### NOAA resources for primary and secondary schools - ocean currents

https://www.noaa.gov/education/resource-collections/ocean-coasts/ocean-currents This introduces concepts and then there are links. One link talks about the "Adopt a Drifter" program. A local charter school (primary) became involved with "adopt a drifter", tracking an oceanic buoy. Kids really...
17. ### Inductor voltages and currents

I have redrawn the circuit as below 40 - (I2+0.5)200 - (I2 + IL)*300 = 0 -> eq1 -(I2 + IL)*300 - IL*280 - 4*dIL/dt = 0 -> eq2 Are my equations correct?
18. ### Back EMF vs Reverse Currents: What's the Difference?

Is it Back EMF, Reverse Current, Reverse Saturation current, Backfeeding? If not, tell the difference.
19. ### 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...
20. ### Analogue Circuits Question -- AC and DC currents through a coil

Summary:: . Hi ,so am currently doing homework , and was wondering if anyone could tell me if i have done my calculations correctly ,because am not 100% sure that i have answer to those 2 questions correctly .If i have went somewhere wrong if you could tell me where and how i could fix it...
21. ### Calculating Magnetic Field Strength and Force of Eddy Currents in a Solenoid

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...
22. ### Ground currents to detect a civilization?

In a scenario where explorers are trying to detect an active, perhaps subterranean, civilization, is it plausible that they would use equipment that measures ground currents (i.e. actual electrical currents in the terrain)? With technology that exists today, would we expect to detect a...
23. ### Opposite Induced Currents in Circuit Explanation

I don't understand why they said that the induced current flow is opposite to each other when it clearly states direction is to the right for both? https://www.physicsforums.com/attachments/285900
24. ### 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.
25. ### B The resistance of an ohmic conductor

I know that the resistance of an ohmic conductor increases with length because the electrons going through the conductor must undergo more collisions in a longer conductor. But why decreasing the cross-sectional area of the conductor also increases the resistance of a conductor?
26. ### Production of the magnetic field from 3-phase currents

This is not a homework problem, I want to calculate the equation of the magnetic field intensity from the 3 phase currents separated by 120Degrees. The 3 currents are ##I_{{aa}^{'}} = I_M\sin \omega t ; -> eq1 \ I_{{bb}^{'}} = I_M\sin(\omega t - 120); -> eq2\ I_{{cc}^{'}} = I_M\sin(\omega t...
27. ### A Superconductor ring: shielding currents in different directions

In this photo you see on the right-hand side that the outer wall current is negative and the inner wall current is positive. That is, they are directed in different directions. But if the applied magnetic field is in the z direction as shown, then shouldn't they both be in the same direction do...
28. ### Determine the currents I1, I2, and I3.

I’m having trouble solving this one problem. Sorry I’m really struggling with currents and I don’t know where to start.
29. ### Optimizing Phase Current Measurements with Shunt Resistors

I have seen an application note of how to measure the phase currents using shunt resistors as shown below I am only confused with the connection when measuring the phase Ia current, it differs from the way the shunt resistor is connected for Ic and Ib, he could have done the same way like Ib...
30. ### Understanding Loop Currents: Why is I3 Negative?

Hello, In the following problem, when finding the equation for I2 I don’t understand why I3 is negative. Although I2 and I3 are going in different directions (clockwise and counterclockwise), at that ohm they are both going from left to right. When finding the equation of I1, I1 goes from left...
31. ### Relations between ##k## Currents & Voltages for Black-Box Device

Hi, I'm aware it is an odd question. Consider a ##k##-terminal electrical device as black-box. We know from KLC and KLV that just ##k-1## currents and ##k-1## voltages are actually independent (descriptive currents and voltages). Furthermore we generally expect there exist ##k-1## relations...
32. ### 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...
33. ### Engineering Calculating Core & Currents for Coils and Cores

I can easily calculate the core and currents required for the coil and core, i get confused do the the external field, any help please.
34. ### Solve the circuit and find all the currents in the circuit

Hello, i have this circuit as a homework. And i have to find all the I's, and Uef, i got stuck at writing Kirchhoff's laws in this circuit, do you think you can help me write them, and also can you explain how can i calculate Uef?
35. ### 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...
36. ### Finding currents using Kirchhoff's laws

Here is my question that I have been trying to do Had tried to attempt it and got there as my answers? Not particularly sure if I had done part b) right from the simultaneous equation I had to solve to get the current values Appreciate for any help! Thanks
37. ### !Measuring Currents in a Circuit w/ Semiconductor

If so, what will I measure in the Ampermeter, the zero total current or the value of the conduction current? I was thinking of the following example- a circuit consist of a current source, an Ampermeter, a switch, and a semiconductor. The semiconductor can have both conduction and displacement...
38. ### Are induced currents of any concern in satellite missions?

A satellite in an orbit around Earth can be subjected to a changing magnetic field (due to eccentricity or angle of orbit or both) which can induce currents on its envelope. Are these currents negligible or are they of any concern to engineers? Also, as I understand it, the satellites high...
39. ### I How Can Neutral Currents Be Detected in Particle Physics Experiments?

In decay processes where no mixing between quark families is present, the mediator of the weak force is the neutral ##Z^0## boson. If that is the case, how is it experimentally possible to detect neutral currents in processes such as: $$\bar{\nu}_\mu + e \rightarrow \bar{\nu}_\mu + e$$ What...
40. ### Total Current running through a wire due to the drawn currents

I made this scenario where I am looking for the total current running through a wire (I_0). I am also trying to model the current running through the wire (I_0) considering the harmonics contributed by the four loads. But since Fourier stated that a complex waveform is the discrete sum of some...
41. ### Engineering Voltages, currents and power between a power plant and a transformer

This is the first part of the problem, which I solved. Now to the second part which I can't manage to find the equations I need to use. Problem: This plant is connected to a 20/0.4 kV transformer of 250 kVA power, through an XP00-A cable (4x150 mm2, IN=300 A, Z1=0.26 Ω/km). a) Calculate...
42. ### Finding the currents in this circuit (2 voltage sources and 3 resistors)

In my attempt, I tried 1) I1 = I2 + I3 Then set up these two equations based on Kirchhoff's second rule: 2) U1 = R1 (I2) + R3 (I3) and 3) U1 + U2 = R1 (I1) + R2 (I3). From what we have 10 = 0.1* I_2 + 0.2 * I_3 22 = 0.1* I_2 + 0.02*I_3 I_3 = 50 - 0.5 I_2 That means I_2 = 233.3 A I_3 = -66.7A...
43. ### 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...
44. ### I How to derive the currents of Z boson and the EM current?

I am a student minor in physics and I am taking this course of particle physics. And I have been lost since the Non-Abelian Gauge Theory which a few lectures before Electroweak unified Theory lecture. i am completely confused and overwhelmed by the math since the mid-term exam, since I was not...
45. ### A Vector and Axial vector currents in QFT

I'm currently working out quantities that include the vector and axialvector currents ##j^\mu_B(x)=\bar{\psi}(x)\Gamma^\mu_{B,0}\psi(x)## where B stands for V (vector) or A (axialvector). The gamma in the middle is a product of gamma matrices and the psi's are dirac spinors. Therefore on the...
46. ### Find the sum of all these electric currents

First, I got rid of amperemeters with 0 values. These are 9. 11 and 12. Amperemeter 4 will show the maximum value of electric current as it is placed directly between E and F. But how to know its value? Will it be 18 mA? I doubt because 18 mA is not said to be the maximum value. All other...
47. ### Rewriting the Ampere's law in term of free currents only

This is not really the assignment of my homework ( my assignment require me to find the magnetic field inside a small air gap on a toroide magnet wrapped with N turns of a wire that carry a current I ) . I'm at some point in the solution where I kind of need to use the rewritten Ampere's law to...
48. ### Using Y to Delta Transformation to Find Currents

Can someone explain why I can't simply use a current divider once I've found the equivalent resistance and source current for the entire circuit? This would look like i0 = 0.044*(113.53/210). Req = 113.53. If it helps, the correct answers appear to be: i0 = 8.28 mA, i1 = 23.6 mA, i2 = 35.8 mA...

50. ### Trick for conserved currents in classical field theory

First I found the equations of motion for both fields: $$\partial_\mu \partial^\mu \psi = -\frac{\partial V(\psi^* \psi)}{\psi^*}$$ The eq. of motion with the other field is simply found by ##\psi \rightarrow \psi^*## and ##\psi^* \rightarrow \psi## due to the symmetry between the two fields...