# The repelling force of a superconductor how strong?

1. Jul 30, 2012

### leviterande

Hi, I posted this earlier in what I thought to be the "General Physics" section, but since it got deleted and I was notified that I posted in "GD" which is (general discussion?) I realised I did this by mistake so I am sorry.

--------------------------
to my question
Hi,

What I learned:
A magnet levitates and gets kind of "fixed" on a superconductor. Also the superconductor can shield two magnets on either sides(so the 2 magnets cant see each other). Both magnets HOWEVER get repelled by the superconductor.

I have been searching and googling for weeks to find an answer concerning the nature of this "repelling force of the superconductor":

Is the repelling force between superconductor & magnet, of the same magnitude and strength as if we were to replace the superconductor with a second identical magnet and facing them north-north ??

Im really confused and Im having a huge headache from sleepless nights of searching and thinking. Your help would be more than great

/
Levi

2. Jul 30, 2012

### Vantenkeist

If the superconductor starts off with no initial current, and a magnet is brought near, then one will be induced in the superconductor. (see Faraday's law of induction). This current that is now set up in the superconductor will persist with little to no resistance (a property of a superconductor). This current will also produce a magnetic field that opposes the original one of the magnet.

In reference to being 'fixed' to a superconductor the only thing I could come up with would be Flux Pinning. Which is basically magnetic field lines being trapped inside the superconductor.

3. Jul 30, 2012

### leviterande

Thanx a lot Vantenkeist for the reply, so let me see if I understand this right:

You said: the current will induce a magnetic field which "opposes" the one of the magnet.

1- By "opposes" do you mean that they kind of repel each other?

2-How strong is "this induced magnetic field", is it equal to that of the magnet?

Thanx

4. Jul 30, 2012

### ZapperZ

Staff Emeritus
Do you know of Lenz's/Faraday's Law?

It would help that you learn the simple stuff first before jumping on "superconductors".

Zz.

5. Jul 30, 2012

### leviterande

Yes I know of Lenz law. As a magnet moves over a conductive material like copper or aluminum current is induced(eddy currents) and therefore magnetic field is created that interacts with the magnetic field of the magnet. How exactly it interacts with the copper is not very understood by me. a lot of things is said on the net. But,It looks like its a phenomena of both repulsion AND attraction at the same time depending on the direction of movement. So at the leading edge of the moving magnet there is attraction and on the trailing edge there is repulsion which will induce a net force of rotating nature as can be demonstrated by rotating an aluminum cylinder under a magnet. Cog wheel relationship in other words(Im not 100% sure)

Its a little different for superconductors... as said I m interested in knowing if the net repulsion force between 2 shielded equal magnets(i.e Superc. wall in between ) is the same as between the same magnets UNSHIELDED?

Thanx

Last edited: Jul 30, 2012