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A conductor that passes a magnetic field, decreases its velocity due to the opposing magnetic forces created by the Eddy Currents.

This "magnetic breaking" effect can be reduced if we change the shape of the conductor from a bar, to a this conductor like this:

enter image description here

What I understand is that conductor above has a higher resistance and reduces the eddy currents. However, what if the air gaps are conductors? Here is where I find laminated conductors to be useful like so:

enter image description here

However, what is the difference? I believe the laminated conductor can carry more current(i/e higher current capacity) than the one above. The whole point is reducing eddy currents(the magnetic breaking)in electric motors, or generators... and not affecting its electric properties by increasing its resistance and reducing its current capacity.

Am I correct here or is my understanding incorrect?

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"Breaking" up the conductor has to do with breaking up possible paths of closed current loops that are induced by a time-varying magnetic field. The direction of the breaks matter as well. For instance, assuming the conducting of your top diagram has thickness coming out of the screen, then the planar breaks need to be coming into and out of the screen. If they run parallel to the screen, then they won't reduce the eddy current by much.

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  • $\begingroup$ What about the current capacity? $\endgroup$ – Pupil May 5 '14 at 22:42
  • $\begingroup$ What is the current capacity? Do you mean the total resistance or the resistivity of the material? I don't believe "current capacity" has a well-defined meaning in physics. $\endgroup$ – Kent May 5 '14 at 22:44
  • $\begingroup$ Sorry, what I mean is current affected in any way? Reduced maybe due to an increase of resistance $\endgroup$ – Pupil May 5 '14 at 22:59
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    $\begingroup$ It has nothing to do with changing the resistance. Breaking up the conductor is purely a geometric effect. Look up "lamination", that's the more common name for it. $\endgroup$ – Kent May 5 '14 at 23:01
  • $\begingroup$ Thus, I wouldn't worry about current being reduced at all... I assumed this would change the conductor's electrical properties too, making it weaker and the amount of current it could carry would be less. $\endgroup$ – Pupil May 6 '14 at 0:46
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I would not say I completely understand your question, but ill explain to you the use of laminating conductors to reduce eddy currents.

First a mistake in your picture, where you say neighbouring loops in opposition, both have current in anti clockwise direction, they are not opposing!

So the thing is that, when a conductor has larger area, larger potential difference is available at its two ends because of interaction with greater magnetic flux, also the current can pass through larger area and hence effective resistance for that current is less; more potential difference and less resistance leads to more current.

Whereas, when we laminate the conductor after making slots in between, we reduce the area and interaction of magnetic flux which leads to development of smaller potentials across the slotted arms of the conductor, the reduced area also results in a higher resistance. These factors "multiply" together to reduce the current in each arm. Even if you add the current of all arms it is still lesser than what was originally available in the unslotted and laminated conductor.

Then again the interaction of stopping mechanism can be closely related to the force obtained by the formula of $\tau = NIAB $. Again smaller current and area multiply together to reduce the breaking effect and even on adding the effect from all arms/teeth it would not be equal to the one which was originally present.

It is helpful economically too, because now lesser metal is required!

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  • $\begingroup$ I understand that by laminating the conductor we reduced the eddy currents but what about the current that can pass within the conductor from a power source? Would there be change? Imagine we had a conductor that had current $I$ that passes through it and we moved it in a magnetic field $B$, would laminating the conductor reduce the current coming from the source? $\endgroup$ – Pupil May 9 '14 at 3:59
  • $\begingroup$ First of all then we would not be talking about eddy currents, and secondly even that would be reduced because while laminating we have removed parts of the conductor, its area has been irreparibly cut down, due to net increases in resistance any constant potential source would give less current now. $\endgroup$ – Rijul Gupta May 9 '14 at 4:05
  • $\begingroup$ There is a system, that requires a conductor to carry a certain amount of current, its it possible to reduce the eddy currents when passing a magnetic field(or in a changing magnetic field). Now, we could break the conductor's area and split the current up from 100A in a large piece into 10Amps on 10 pieces and that would be a reasonable solution? Maintaining the same total current, and reducing eddy current losses? $\endgroup$ – Pupil May 9 '14 at 8:52
  • $\begingroup$ It would indeed be the same total current, but since I haven't seen/read about any such device I would not comment much on it until I get to know something about it. $\endgroup$ – Rijul Gupta May 9 '14 at 10:19
  • $\begingroup$ I agree, its just a theory until practiced I guess. Yet from all the principles of EM, it should work. Reduced Eddy currents and same value of current but divided into multiple conductors. $\endgroup$ – Pupil May 13 '14 at 0:18

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