Currents Definition and 497 Threads

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. Kerrigoth

    Are induced currents created by motion or change in flux?

    The book I am working through is beginning to dive into induced currents and Lenz's Law. When a conductor is moving perpendicular to a magnetic field, the charge carriers inside will experience a magnetic force; This causes the charges to move. Eventually, the electric field from the charge...
  2. S

    Use of the conservation equation for Noether currents

    Homework Statement Given that ##\frac{dQ'}{dv} = \frac{1}{c^{2}} \int d^{3}x \bigg[ x \big( \frac{\partial \rho}{\partial t} - \frac{v}{c^{2}} \frac{\partial j^{x}}{\partial t} \big) - j^{x} \bigg] \bigg|_{t = \frac{vx}{c^{2}}, x, y,z}##, use the conservation equation ##\partial_{\alpha}...
  3. R

    AC Homework: 10 Ohms Resistor, 12 uF Capacitor, 28 mH Inductor

    Homework Statement A 10 ohms resistor, a 12 microFarad capacitor and a 28 mH inductor are connected in series with a 170 V generator. A.) At what frequency is the rms current maximum? B.) What is the maximum value of the rms current? Homework Equations A.) Fo = 1 / 2pi sqrtLC b.) Irms = Vrms...
  4. A

    Two different ways? (probability denstities and currents)

    Hi, I would appreciate some help with this issue: I want to calculate the probability denstities and currents from the Schrödinger and Klein-Gordon equations, and I've found 2 ways so far, the one that gives the "standard" result (the one I've seen on my course, or wikipedia) but I don't...
  5. A

    Solving Resistor Circuits: Find Currents in R & 10Ω Resistors

    Homework Statement The resistor R in the above figure has a resistance of 19.1 Ω. a. Find the current in the resistor R. b. Find the current in the 10-Ω resistor. 2. Homework Equations Kirchhoff's Laws (Junction Rule and Loop Rule) V=IR The Attempt at a Solution I figured out part a (I...
  6. A

    Finding Currents Using Kirchhoff's Laws

    Homework Statement a. Determine the currents I1, I2, and I3 in the above figure. Assume the intermal resistance of each battery is r = 2.48Ω. Homework Equations Kirchhoff's Laws (Junction Rule and Loop Rule) The Attempt at a Solution Using Kirchhoff's Laws, I ended up with three equations...
  7. A

    Solve Currents Homework: Kirchhoff's Laws

    Homework Statement Determine the magnitudes of the currents through each resistor in the above circuit. The batteries have emfs of E1 = 9.2 V and E2 = 13.8 V, and the resistors have values of R1 = 11.8Ω, R2 = 29.3Ω, and R3 = 34.3Ω. Use positive numbers for currents to the right, and negative...
  8. T

    Calculating Voltage Difference in a Circuit: Am I on the Right Track?

    Homework Statement Homework Equations V=Ir The Attempt at a Solution I solved part a ) already my question is about part b). Let's say I know that the 6 ohm resistor has current I3 going across is pointing to the left, and the 3 ohm resistor has current I1 also pointing to the left across...
  9. Logan Land

    MHB How to find currents and voltages with 2 batteries connected?

    Assume that this circuit has been connected as shown for a very long time. Re-draw the schematic and label the currents and voltages in and across all components including the batteries. All components are “ideal.”
  10. 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...
  11. D

    Two parallel wires carrying currents in the same direction.

    Homework Statement Two parallel wires both carry currents directed from left to right. A circular wire loop lies in the plane of the two wires midway between them. The currents are positive charges. Sketch the changes in the magnetic fields induced and the resultant current direction in the...
  12. jake jungle

    DC current -- Find the 3 currents in this Battery + Resistor circuit

    Homework Statement Find I1 , I2 and I3 Homework Equations I = E / R I3 = I1 - I2 The Attempt at a Solution its the trouble with parallel different emf . I know a formula how to combine them into one but it needs inner resistance . i don't know how to do it with the ideal circuit . The...
  13. V

    Sum of currents in protection relay

    In a differential protection relay there is a setting of a threshold for the sum of amps (or the squares). In what way would that be of interest? The relay is an Areva P521. Also, the relay can display the ratio between the positive sequence current and the negative. What information does that...
  14. B

    Instantaneous currents in RLC Circuit

    Homework Statement I am completely stumped on this problem: In this circuit: v= 30.0 R = 400 ohms C = 2.50 micro coulombs L = .300 H The switch (pretend you see one) is close at t=0 Current i1 flows through L and current i2 flows through C QUESTION: At what time (t) does i1=i2 ...
  15. S

    Is electric current only a flow of charge?

    A magnetized object is always described as having bound volume and surface current. Are these bound currents real? I mean if I connect a galvanometer between two points on the surface of a magnetized iron sphere, will the galvanometer show a deflection? If it does then it is very strange because...
  16. P

    Help with thyristor currents please

    Hi, I want to use a 2n5062 thyristor as a switch to output a current when the thyristor is on. I have found a data sheet which has values for gate trigger current and holding current (200 microamp and 5 milliamperes) respectively. Am I correct in thinking I must apply at least the gate trigger...
  17. EngUOL

    Why Use Radians to Measure AC Sin/Cos Signals Instead of Seconds?

    Could someone please explain why is chosen to measure ac sin/cos signals with radians instead of seconds? If ac waves is the behavior of a wave over time? Any feedback would be appreciated. Thank you!
  18. M

    Currents on a three phase system

    Hi everyone, is it possible to sum at any given moment in time L1 + L2 + L3, algebrically speaking? If so, what would this value represent? Thanks
  19. J

    A function generator that cannot kill you? Very low currents.

    Hi, I am looking for a function generator that if you hooked up to yourself, wouldn't kill you. I need something that can output very low currents through the skin without harm. Honestly a 9V battery causes too high of a current for my purpose, but I do need to very finely tune the current. Can...
  20. Sol_Engineered

    Should same values of currents be used in Kirchoff's laws?

    Homework Statement See above diagram for full details of the circuit Variables used: Assumption: direction of current is clockwise and the loops are positive in clockwise as well. Current through 1000 ohm=i1 Current through 4700 ohm-i2 Current through 2200 ohm=i3 Current through 1200...
  21. X

    Force between Electric currents

    Homework Statement [/B] In a typical experiment to study the force between electric currents, identical fixed and movable wires were separated using a spacer thickness 0.6065cm. The radius of each wire was determined to be 0.162cm and the length of the movable wire was 26.5cm. The apparatus...
  22. R

    Finding currents in branches of a circuit

    Homework Statement The 5.00-V battery in the figure (Figure 1) is removed from the circuit and replaced by a 20.00-V battery, with its negative terminal next to point b. The rest of the circuit is as shown in the figure. Part A ) Find the magnitude of current in the upper branch. Part B )...
  23. G

    Finding Unknown Currents in a Two-battery Complex Circuit

    Homework Statement Look at the circuit given in figure 1. Solve for the three currents, I1,I2,I3. Homework Equations KVL: Sum of voltages in a closed loop equals zero KCL: Sum of currents entering a junction equals the sum of currents exiting a junction Ohm's Law: V=IR NOTE: Nodal analysis...
  24. G

    Calculating Geostrophic Flow and Pressure Gradient | Station J and K Example

    Homework Statement Station J is 100 km West of station K at 30o N. The sea level difference between the two stations is +0.10m. What is the geostrophic flow between J and K, and what is it's direction? Specify and justify any assumptions you make. Homework Equations What is the pressure...
  25. Fyr554

    How Do You Calculate Current and Phase Angle in AC Circuits with Missing Data?

    Homework Statement part 1 Consider the circuit of figure G, where R1=20 ohms R2=10 ohms X1=37.7 ohms X2=-53.1 ohms. Compute the current and the phase angle between the current and the applied voltage. In the figure R1 is in series with X1 and R2 and X2 are in series. R1 and X1 are in parallel...
  26. Breo

    Calculating Noether Currents in Peskin & Schroeder QFT

    Hello folks, I do not know the calculus behind used to obtain both currents in this page from Peskin and Schroeder QFT book. $$j^\mu = \partial^\mu \phi $$ and the 2.16 eq. http://www.zimagez.com/zimage/capturadepantalla-280914-033510.php How do you calculate them?
  27. M

    Need help with solving currents using mesh analysis

    Homework Statement i can't write the problem text as it is a circuit [b]2. Homework Equations I labelled the meshes as clockwise shown on the image KVL: The sum of voltages around a loop equals zero The Attempt at a Solution i1 = 8A i2: 19(i1 - i2) - 5.54(i2-i3) = 0...
  28. almarpa

    Non stationary currents and Ohm's law.

    Helo all. Stationary currents are those whose current density is constant in time. On the other hand, ohm law claims that in certain materials, current density is proportional to electric field within the material. So, if the electric field is stationary (constant in time), the current...
  29. arivero

    Chiral leptoquarks and vector currents

    In a comment http://motls.blogspot.com.es/2014/07/cms-sees-650-gev-leptoquarks.html#comment-1479399237 to Motl's blog, there are some reference to "chiral leptoquarks". I am guessing that this is an object which is not a Dirac fermion, ie it only exists one of the two chiral components of it...
  30. Maxo

    Illustration of convection currents

    When convection currents are illustrated they are often painted as arrows with red and blue color, the red one being the direction of warmer currents and the blue ones being the direction of cooler currents. See for example this picture: But how does this go together with the fact that heat...
  31. B

    Derivation of Noether currents under Lorentz Transformation

    Is there anywhere I can see the explicit derivation for a massless real scalar and for the EM field? thank you.
  32. JasonHathaway

    Determining two diodes' currents

    Homework Statement Assuming that D1 and D2 are ideals, determine ID1 and ID2 according to the table below. Homework Equations Circuit Analyzing methods (KVL, etc...) The Attempt at a Solution I've confirmed my solutions for the first three cases with final answers of the book...
  33. M

    MHB Mesh Currents with Differential Equations

    I've attached a picture of the problem statement, figure, and of my work so far. I'm trying to use mesh currents and then differentiate it, but I really have no idea if I'm on the right track. Also, I don't understand why i1 isn't just V/R (The physical current is the mesh current for R1...
  34. M

    MHB Mesh currents, emfs, and resistances

    Howdy! Looking for help with the following problem (#33). I found it easiest to take a picture of the problem statement and the figure and another of my work (I am working on learning LaTeX so I can write them neatly in posts, but until then, I hope a picture is sufficient). I got the system...
  35. C

    Was the direction of oceanic currents changed during the ice age?

    Yes, curious about that. (No, I'm NOT asking about some short term disturbances when glaciers were melting, but whether with lower temperature and part of continental shelf above water caused the currents to change their direction)
  36. A

    Analyzing the LCR Circuit: Oscillatory Currents

    Homework Statement I have the LCR circuit attached below. At time t=0 the capacitor is uncharged and the switch is closed. By solving an appropriate differential equation, show that the current through the resistor is oscillatory provided L<4CR2. By considering the boundary conditions at...
  37. M

    What Happens When High Current Hits a Car's Electrical System?

    Hello, My question is out of curiosity and pertains to transient currents and their possible effects on any electrical equipment. For example, The various electrical components(infotainment systems, headlights, radio etc) in a car are “grounded” on the chassis, If a live wire from a electricity...
  38. P

    Why do eddy currents cause oscillations to die away quickly?

    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...
  39. D

    Differential Amplifier find currents, and Gain

    Homework Statement For the differential amplifier circuit given above, for all transistors except Q1 and Q2 we have: β=100, VA=80 V, RC =20 k, VT=0.026 (Thermal voltage), VBE(on)=0.7 V a-Determine the collector currents IC1, IC2, IC3 and IC6 b-Calculate the Differential mode voltage...
  40. Q

    Unbalanced Phase Currents in 3~ Motor

    A 3-phase induction motor in our factory had unequal phase currents. One of the currents was nearly normal while the other two were about twice the usual value. Somebody said that prolonged running causes increase in resistance of stator winding, and this results in increased current. But this...
  41. I

    What is the force direction on a left wire in a parallel current setup?

    Homework Statement Two current carrying wires run parallel. The bottom wire creates a magnetic field at a point on the top wire. What direction is the force on the left wire? --------->------ --------->------ Homework Equations I'm assuming there's no equation, just the right hand...
  42. U

    Directions of currents in Kirchhoff's 2nd law problems

    Homework Statement Apply Kirchhoff's laws to find the current at point X in the circuit shown. What is the direction of the current? Homework Equations V = IR Kirchhoff's 1st law: ∑Currents entering junction = ∑Currents leaving junctions Kirchhoff's 2nd law: ∑EMFs in a loop =...
  43. J

    Convection Currents Explained - No Pressure Difference

    Hi, please could someone explain how a convection current occurs. There are a few different explanations I have come across which in my view are not consistent. Warm air rises, becomes less dense and due to its buoyancy will rise. What mechanism causes the cooler air to replace this air? Some...
  44. J

    Household currents physics homework

    Homework Statement Typical household currents are on the order of a few amperes. If a 1.60A current flows through the leads of an electrical appliance, how many coulombs pass through it in 6.50min ? Homework Equations I=ΔQ/Δt The Attempt at a Solution 6.50min=1min/60s= 0.108s...
  45. D

    Electromagnetic force between Parallel Currents

    Hi, sorry if this has been asked before. It is known that two parallel wires carrying electric currents in the same direction attract one another. The force is known as electromagnetic force. My question is whether this has been checked for two pure currents of charges. Specifically, whether...
  46. TrickyDicky

    Displacement and conduction currents

    One thing that I don't intuitively get about these currents is that in the conduction current the electric field is supposed to be static at each point of the conductor(there is no assumption of current intensity change), whilst the displacement current is defined as a varying electric field...
  47. Spinnor

    ψ in formula for strong force currents, how many components?

    In the ψ below, there are 4 components for the Dirac spinnor times three possible color states for a total of 12 components for ψ? Are there low energy, weak field limits of the above that allow us to consider classical color counterparts of electric current densities and electric charge...
  48. K

    The interpretation of noether currents in scalar QED

    In scalar QED, there are two noether currents ##J_{global}## and ##J_{local}##corresponding to the global and local gauge transformations respectively. In QED, the two currents are exactly the same. But in scalar QED, they are totally different. $$J_{global}^\mu=i e (\phi^\dagger...
  49. C

    Mathematical Model for Convection Currents

    I have a difficult problem on my research exploration for math. I am modeling the convection currents of boiling water in a pot, which is heated by an electric stove. There is a constant supply of energy at 8000 watts (the average for a stove) that heats the pot from the bottom of the pot...
  50. michael879

    Symmetries + Conserved currents of SM

    Can anyone give or point me to a list of ALL continuous symmetries in the standard model, and the conserved currents associated with them? I've spent a lot of time looking and for the most part everything I find is very abstract, where as I want the specific details to the SM (i.e. SU(N) gauge...
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