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On the electromagnet setup pictured below, only the core part is magnetic (when powered, it attracts a piece of steel) but not the 2 "wings" outside that are supposed to channel the magnetic flux.

Why is that?

setup

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    $\begingroup$ Are you 100% sure that when energized the outside of the steel bundle has no magnetic field whatsoever? You might need a magnetometer to tell. I'm guessing that the coil is maximizing the flux in the center, as it should. $\endgroup$ – willpower2727 Sep 6 '16 at 11:55
  • $\begingroup$ yes there is a super light magnetic field compared to the core, What I dont understand is that they should be equal, and what I get is very very far from it $\endgroup$ – Manu de Hanoi Sep 6 '16 at 12:34
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The strength of an electromagnet's field will typically be strongest on the inside of the coil (talking about a normal electromagnets). This is true for the geometry of the magnet you've shown in the question.

When you run a current through the coil, magnetic fields (perhaps not the best way to phrase this) are produced along the path of the coil that are always perpendicular to the coil. You can see an illustration of this below in an image on Wikipedia's page on electromagnets:

enter image description here

Taken from: https://en.wikipedia.org/wiki/Electromagnet#/media/File:Magnetic_field_of_wire_loop.svg

What you can observe is that in the center of the coil the magnetic fields produced along the path of the coil tend to converge (geometry dependent). On the outside of the coil these fields diverge from each other. It should be easy to see that the field strength inside the coil will be stronger than the outside.

The configuration of your electromagnet is a little confusing. The coil is oriented perpendicular to the long axis of the core, which means the "wings" as you call them don't really get a strong field as they are outside the coil. If the coil was rotated 90 degrees so that the core was aligned with the long axis of the coil then I would agree that the field should be strong throughout the whole core.

I'm no physicist, this is the easiest way I can explain it. If someone else can produce a more technical answer you'd benefit more from that.

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  • $\begingroup$ Hi This core is taken from a E I shaped transformer (without the I on top). The coil axis is the same a the central core,if insulation was removed you'd see the coil coiled around the central core. The core and wings material are supposed to channel most of the magnetic flux, the wings are connected to the central core at the bottom (E letter shaped). This is how transformers are built and transformers just move the magnetic flux from one coil to the other, as much of it as they can . google.com/search?q=EI+transformer $\endgroup$ – Manu de Hanoi Sep 6 '16 at 15:36
  • $\begingroup$ @ManudeHanoi that would have been good to know in your original question :) Are you applying AC or DC to the coil? What voltages? $\endgroup$ – willpower2727 Sep 6 '16 at 15:54
  • $\begingroup$ sorry for giving so little info in the 1st place. I am applying DC for now, tried 5 V and 24V. I intend to use AC later $\endgroup$ – Manu de Hanoi Sep 7 '16 at 4:32
  • $\begingroup$ @ManudeHanoi I suppose it doesn't matter if you apply AC or DC if you are only interested in the magnetic field and not transforming anything. AC of course will produce an alternating magnetic field. I maintain my original perspective that I'm not surprised the magnetic field is weaker on the outside wings. Even in a toroidal transformer the field would be weaker on the outside. $\endgroup$ – willpower2727 Sep 7 '16 at 12:04
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    $\begingroup$ @ManudeHanoi it's an interesting question, and I was hoping someone else would interject with a better answer. You might consider asking this on the physics stack exchange. $\endgroup$ – willpower2727 Sep 7 '16 at 12:07

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