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# Physics/Magnetic repulsion

Question

Magnetic repulsion
Hello Steve,

Thanks for volunteering on this site, it is a great resource.
I am interested in using an electromagnet to lift a permanent magnet by repelling it, and I am wondering if you could please tell me whether I have understood the science involved correctly.
In the the section labelled Pic 1 in the attached image, a permanent magnet sits on top of an electromagnet, which is switched off. Here I have assumed that the permanent magnet would be attracted to the ferrous core of the electromagnet - is this correct?

In the section labelled Pic 2, the electromagnet is turned on. It repels the permanent magnet, lifting it up.
(The permanent magnet is mechanically fixed in a way not shown here, so that it can move up a certain distance and back down again, but not side to side.)
Is this what would happen? Have I understood this correctly, or am I missing something important? Would the magnets behave in the way shown?

Thanks very much for reading this question.
Best regards,
Eddie

Correct, but two things.  1)  The current, as drawn, would have to go down the coil so that, by the right hand rule, it could induce a magnetic field in the core which would point down.  That would mean that the south magnetic pole would point up, repelling the magnet.  2)  The current would have to magnetize the core enough to overcome the induced magnetism from the permanent magnet, so it would have to be quite strong.  Otherwise, you end up with a frustrated state of magnetic moments in the core.  Once you overcome that and the permanent magnet gets the least separation, you get runaway repulsion at first, followed immediately by dramatic weakening as the magnets separate.  This repulsion is completely unstable, the magnet would fly off at some angle determined by tiny initial conditions and probably quickly rotate and slam back into your coil, unless you had it on some sort of a guide.

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.