4
\$\begingroup\$

I bought an electromagnet online hoping to make it attract and repel metals by changing the polarity of the voltage on it, but I ended up experiencing attraction all the time.

Is there any way to make an electromagnet that attracts in one way and repels in another way?

\$\endgroup\$
6
  • 6
    \$\begingroup\$ The only thing that you can "repulse" with an electromagnet is another magnet. \$\endgroup\$
    – Dave Tweed
    Jan 16 '16 at 17:10
  • \$\begingroup\$ @DaveTweed one may also repel superconductors under suitable conditions. \$\endgroup\$ Jan 16 '16 at 19:27
  • \$\begingroup\$ @OleksandrR.: That's because a superconductor becomes an (electro)magnet when pushed into an existing magnetic field. \$\endgroup\$
    – Dave Tweed
    Jan 16 '16 at 19:28
  • \$\begingroup\$ @DaveTweed no, a superconductor excludes all magnetic fields from itself. It is not itself magnetized. Some types of superconductor are capable of flux pinning, but the effect is different and will not lead to repulsion. \$\endgroup\$ Jan 16 '16 at 19:29
  • 2
    \$\begingroup\$ @OleksandrR.: A superconductor excludes a magnetic field by allowing a current to flow, which creates a new field that exactly balances the external field at the surface of the superconductor. I call that a magnet. \$\endgroup\$
    – Dave Tweed
    Jan 16 '16 at 19:31
5
\$\begingroup\$

For a magnet to repulse something, that something needs to also be magnetized and the like poles of the two magnets aligned.

The electromagnet attracted everything magnetic because those other things weren't polarized with their own magnetic fields. Two electromagnets, or the electromagnet with a permanent magnet would work.

\$\endgroup\$
2
  • \$\begingroup\$ If I have an electromagnet with an iron core, and I align it was a strong neodymium magnet with it so as to repeal, is it possible for the neodymium magnet to reverse the domains in the core and stick to it if I bring it close enough? \$\endgroup\$
    – blueether
    Feb 28 '20 at 6:48
  • \$\begingroup\$ @blueether No. The worst that can happen is that the neodymium magnet will flip polarity itself, but then you will need a very strong electromagnet. \$\endgroup\$
    – fishinear
    Jul 12 '20 at 12:07
3
\$\begingroup\$

A coil that is energized with alternating current will repel a conductive but not magnetic ring.

enter image description here

\$\endgroup\$
3
\$\begingroup\$

Reversing the polarity on an electro-magnet will reverse its poles but it will still be a magnet.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Reversing polarity on electromagnet reverses poles.

Thought experiment: if you had purchased a bar magnet and found that one end of it attracted metals, would you have expected the other end to repel?

schematic

simulate this circuit

Figure 2. Unlikes attract. Likes repel.

\$\endgroup\$
0
\$\begingroup\$

It is possible to make an electromagnet repel a permanent magnet. To accomplish this the electromagnet's current needs to induce a magnetic field "He" in the core which is stronger then the opposite field Hm that the magnet is inducing on that same core. If |He| > |Hm| then the core is magnetized by He-Hm, a net field whose polarity depends on the direction of the applied current. Normally a pretty strong current is required to overcome Hm, making it appear that the magnet always attracts the core.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.