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.
I have read that locomotives use eddy current braking systems, and one article mentioned that this system has also been used to charge batteries in a recovery circuit. However, I can not find details on this idea. From what I understand, the train has conducting discs attached to the wheels, and...
My question:
Should the sum of all bound currents always be zero?
For example, should the bound currents of a cylinder with both bound volume current density and bound surface current density always sum up to zero?
Does the uniformity of current ran through the cylinder have any effect...
Suppose we are looking at the cross-section of a cylindrical current-carrying wire. Due to the motion of the electrons in the wire, it can be said that at all points at the surface of the wire a magnetic field tangential to the wire exists. Since there are electrons moving in that region as...
Suppose we have a current-carrying wire and an electric charge which is moving parallel to the wire with the same speed and direction as the electrons in the wire. The wire produces a magnetic field which acts upon the charge through a force. From the charge's reference frame, though, no...
Homework Statement
In the figure 29-49, four long straight wires are perpendicular to the page, and their cross sections form a square of edge length a = 20 cm. The currents are out of the page in wires 1 and 4 and into the page in wires 2 and 3, and each wire carries 19 A. What is the...
I don't really understand what is eddy current. Is it just the current that is formed using Lenz's law? Or is it different? My idea of eddy current is that it is of many small swirls all over a metal plate that opposes the force exerted to move the plate.
Thank you.
I understand pretty much everything related to this, except how many currents should I put when arbitrarly putting them. The number of resistors? The number of wires? The number of loops?
I'm seriously lost here, thanks!
Homework Statement
A solenoid with an iron core inside it is connected in series with a resistance to a battery. What happens to the defelction in the ammeter connected in the circuit when the iron core is suddenly removed?
Homework Equations
Inductive reactance = wL
Induced e.m.f. = -...
I am doing some work with electric circuits and just have a general question. With the concern of a given current in three branches of a circuit, is the total current the sum of the current through the resistors? Are they all equal, or does half of the current flow through each resistor? I think...
Homework Statement
If you put a POSITIVE test charge in an electric field, does it move toward a higher or lower potential? If you put a NEGATIVE test charge in an electric field, does it move toward a higher or lower potential?
Homework Equations
The Attempt at a Solution...
Referring to the bridge circuit of fig P90, if I=6A, I2=4A, and I3 = 0, find I1, I4, and I5.
I did,
I1=2A
I4=4A
I5=2A
My logic being, since I is 6A, and I2 is 4A, I1 must be the difference, 2A. since I4 is coming from I2 and I3 it should be the sum, (0 + 4A = 4A). and I thought because I5 is...
the title says it all...
my question is simple... are there transistors easily available that can be configured to provide upto 3ampers in the saturation region? if yes, whch ones?
Homework Statement
It is given that when a copper or aluminium bar is set in oscillation in a magnetic field eddy currents are produced inside the bar. Should it be necessary that the bar should be made of a non-magnetic substance such as copper, aluminium etc.? Can it be a ferromagnetic...
I know that when you cut magnetic field lines with a wire you get an electric current.
I know that if the left side of your screen was a magnet with its south side facing the north side of an other magnet which is the right side of your screen, and a wire coming in from the top of your...
There are two AC current carrying conductors.(both are of the same frequency)
How do you compare the currents to know if they're not equal at all times...?
Please Answer as soon as possible ...
A solid metallic body moves closer to a magnet. This causes increase in magnetic flux linked with the body. Eddy currents are generated in it.
Now, the problem is: will the body come back to its original position or will stay there?
I say that eddy currents will generate heat which will go...
Hello, I am a mechanical engineer by education and I am working on a multi disciplinary problem. I regularly work with eddy current dynamometers at work and I am curious about the materials used within the rotor and stator of these dynamometers.
First off, this isn't a homework problem per...
Throughout the electric force/field and magnetism unit, there's always a rule that involved using the left hand and the right hand. I'm a bit confused on how to apply the rules because of the units are applied to different fingers. If someone could give me an explanation on it, that'd be great...
I have these two circuits with permanent rule:
a)
b)
I'm asked to find:
For a): the charges of each capacitor (C = 1 \muF)and the currents in each resistance.
For b): the currents in each branch with the L switch on and off, the difference of potential between A and C, A and B and C...
A circular wire ring of diameter 18 cm carries a current of 5.0 A directed as indicated in Figure P.51. A moving electron just happens to be passing through the neighborhood. When the electron is at the center of the circular ring and moving at speed 2.50 multiplied by 106 m/s in the direction...
Two infinitely long straight wires lie in the same plane and carry the currents depicted in Figure P.48.
(a) Find the magnetic field at the point P located 24 cm from the intersection of the wires along the bisector of the acute angle between them.
(b) Find the magnetic field at the point S...
1. In the circuit of the figure, find the current supplied by the battery.
2. Find the current through the 6\Omega resistor.
Attempt at a solution:
To find the total current supplied by the battery I tried:
\frac{6*4*2}{6+4+2} = 4\Omega
Then I did that resistance in series with...
Not sure if this is the right place to ask, but this doubt originated when reading on string theory and so here it goes...
The general canonical energy-momentum tensor (as derived from translation invariance), T^{\mu\nu}_{C} is not symmetric. Also, the general angular momentum conserved...
Hello, I'm not sure where to post this so I hope this is the right spot. It's not a homework question, just a concept I need to get straight before an exam ;)
If I'm pulling a sheet of metal through a uniform magnetic field (which is perpendicular to the sheets motion), Eddy currents are...
Okay, I'm sure I must have overlooked something very trivial, so please help me with this:
Two parallel infinite line currents of equal magnitude attract each other. The current can be thought of as consisting of positive and negative particles with equal linear densities, but each moving with...
Okay so i just want to make sure i got this right because its a kind of confusing topic for me. So eddy currents are caused because when there is a motion (with a conducting surface) through a magnetic field a current is induced? and because there is a current there is also a magnetic field due...
1. A 50 g horizontal metal bar, 12 cm long, is free to slide up and down between two tall, vertical metal rods. A 0.060 T magnetic field is directed perpendicular to the plane of the rods. The bar is raised to near the top of the rods, and a 1.0 Ohm resistor is connected across the two rods at...
Iv started physics electronics literacy at university as a requirement for my degree, i didnt do science at school and I am very confused with what's going on..How to a determine a current in the resistors, please can someone give me a step by step on how they got to the answer...i have uploaded...
Homework Statement
I have to show that the vector current \vec{V}^\mu = \overline{\psi} \gamma^\mu \vec{T} \psi and the vector axial current \vec{A}^\mu = \overline{\psi} \gamma^\mu \gamma_5\vec{T} \psi satisfy this
\partial_\mu \vec{V}^\mu = i\overline{\psi}[M,\vec{T}] \psi...
(Solved.) 2 Unknown Currents, 1 Unknown emf, and a little confusion to boot!
First off, hello everyone! I just formally joined the forums today after reading discussions from the shadows for a while now.
This summer I'm taking the second part of a 200 level physics course and the...
A number of years ago I required a low voltage, extremely low current, voltage regulator.
Normal Zener diodes do not function well at low currents.
I became aware that the forward voltage of red LED's was approximately 1 Volt at even extremely low currents (less than 1 microamp).
My...
I've read that when currents in two parallel wires are going in the same direction, they attract each other. The same text said that when the currents are going in opposite directions, the two wires repel each other. now i can't porve this for myself as i keep making the folowing mistake
can...
I'm guessing it has something to do with the fluid gaining thermal energy from the heat, the heat makes the molecules repel each other further so the fluids volume expands?
if not why do fluids expand with heat?
-
the rest is mandatory, after expanding the volume increases, decreasing the...
Homework Statement
Consider two small conductive spheres in radius a and b located far from each other.
In t=0 "a" sphere charged with Q and "b" sphere neutral. We connect the spheres by wire with resistance R.
Find the charge on each sphere as a function of time.
Homework Equations...
given the following:
http://lh6.ggpht.com/_H4Iz7SmBrbk/Sg04JIIg9vI/AAAAAAAAA-o/xDycbG90Gmc/s720/C.jpg
and given that
ε1=3V
ε2=2V
R1=1Ω
R2=2Ω
R3=3Ω
i am asked to find the current flowing throiught R1,R2, R3
what i did was
I3=I2+I1
I1R1-I2R2=ε1
but i am short of one...
Homework Statement
A capacitor is charged through one bulb and then discharged through two bulbs. Mark each of the following statements true or false.
a) The same amount of charge flows during charging and discharging.
b) More charge flows through the single bulb than through the two...
Homework Statement
A coaxial cable has a linear insulating material of magnetic susceptibility \chi_m separating the conductors. A current I flows down the inner conductor and returns along the outer one. Find the magnetic field in the region between the tubes. As a check, calculate the...
The point of the lab was to determine the vert comp of the Earth's mag field by measuring the deflection of a current-carrying wire stretched between 2 supports.
I took measurements of the deflection with the current flowing in one direction and my partner did the same but with the current...
Homework Statement
When a wire carries an AC current with a known frequency you can use a Rogowski
coil to determine the amplitude Imax of the current without disconnecting the wire to
shunt the current in a meter. The Rogowski coil, shown in the figure, simply clips
around the wire. It...
Homework Statement
Your friend wants to be a magician and intends to use Earth's magnetic field to suspend a current-carrying wire above the stage. He asks you to estimate the minimum current needed to suspend the wore just above Earth's surface at the equator (where the Earth's magnetic field...
Homework Statement
Find the three currents in the image.
Homework Equations
Khirkoffs laws
Sum of currents equal zero.
The potentials around a closed loop add up to zero.
The equations given in the solution are
-2I_1 + 12I_2+6=0
-12I_2+8 = 0
I_1+I_2+I_3=0
The Attempt at a...
Homework Statement
Is the current at all points the same? If not then what is the order from highest to the lowest?
http://img141.imageshack.us/img141/2418/currenthn9.th.jpg
Homework Equations
The Attempt at a Solution
Hi all -- I'm writing a controller for an interferometer and I need to be able to control the voltage across a terminal and read the current from a photodiode in c++. What would be a good, reasonably priced peripheral that would accomplish this, preferably with linux support?
Better yet, is...
Hey, I have this QTI sensor ( circuit is shown, the left schematic ) and I am trying to get it to detect a white line only, no red,blue or green just a white line. 5 volts is applied to the pin called White(top pin). Now when the IR light is emited from the IR LED will the Ie, emiter current...
Out of curiosity is it possible to generate a split second of an electrical current which would be more of an electrical signal by literally boucing an electrical conductor off of another electrical conductor, such as copper hitting copper sending the electrons flying down the current or would...
Homework Statement
Hi all.
Please take a look at the attached circuit. I've have found the amplitude of the current through the resistance to be:
\left| {I_0 } \right| = \frac{{\varepsilon _0 }}{{\left| {R - \frac{R}{{\omega ^2 LC}} + \frac{i}{{\omega C}}} \right|}},
where ε_0 is the...
Homework Statement
The preceding problem was an artificial model for the charging capacitor, designed to avoid complications associated with the current spreading out over the surface of the plates. For a more realistic model, imagine thin wires that connect to the centres of the plates (see...
Hello everyone!
I have been searching all over the internet for an answer to this question:
will moving a magnet within a coiled wire induce a current even if the magnet "stays" within the coiled wire for a matter of seconds?
I am planning an improvement to an experiment where a magnet...