All things magnet...

Are “natural” magnets manufactured or refined? Is there a limit to how strong a natural magnet can be? Does a magnet ever lose it’s magnetism? Is it possible to have a magnet with every side a “north” polarity? Does non-magnetic material shield/contain/absorb magnitism? Is there any substance that does…(like lead can contain radiation)? Do magnets with opposing magnetic fields produce heat or friction (Like the magtrains in Japan and DisneyWorld)?

On a larger scale…why does the earth have a magnetic field? Is it because the core rotates…or is there an electrical current running thru it?

What is a magnetic bottle and what does it have to do with having a workable fusion reactor?

Some magnet FAQs.
Magnet Facts.
Natural magnets: lodestones.

AFAIK, no. A magnet has a “north” pole and “south” pole.

What you are referring to is known as a “magnetic monopole”. They have been predicted by some physicists, but have yet to be observed.

A fusion reactor works by fusing atomic nuclei (typically hydrogen in man-made reactors, although stars can fuse heavier elements). In order to fuse hydrogen nuclei, the electrons must first be stripped off. This is done by way of intense heating, resulting in a phase of matter known as plasma. Plasma is just the state where electrons are no longer bound to the nucleus, resulting in a super-heated gas of ions.

Plasma would melt right through any physical barrier we would care to build, but since it consists of ions, plasma can be contained by a magnetic field without having it come into contact with other matter.

Thus a magnetic bottle is simply the name given to an arrangement of magnetic fields that is closed (usually in a torus shape) so as to contain the plasma.

Or it could have no poles.

AFAIK, that would be impossible. The point of the magnet is that overall, the plus and minus ends of the molecules are aligned together, making one side more plus, and one more minus. This then exerts a pull on substances that can let their molecules twist a bit to align and be significantly attracted to the magnet.

There’s probably something wrong in that, but I think I’m close.

There is, however, a neat arrangement called a Halbach array that concentrates nearly all the magnetic flux on one side of a composite magnet (though with alternating polarity).

Maxwell ecuations state that:

div B = 0

This simple equation says that if you draw ANY closed surface, magnetic flux coming in and out of this surface must be equal. Magnetic flux is represented by the field lines that go from north pole to south pole. You can use this to prove that a magnetic field line must be closed, so there is always a north and a south in any magnet.

The existence of a magnetic monopole is in contradiction to this, and is yet to be proved.

Donut-shaped magnets have been around for 100 years. The magnetic field resides inside the magnetic in a circular fashion. As a whole, it has no north pole and no south pole.

A wire carrying a current produces a magnetic field around the wire. Like the donut-shaped magnet, this field has no north pole and no south pole.

I don’t understand this. Every kid knows that these magnets will repel each other if arranged properly, and will stack up “magically” with a pencil put through the hole.

If you drop some magnets, they can lose their magnetism, thought I’m unsure of the precice process. I’d recommend perhaps looking around here.

BTW, a type of magnetic bottle is used in anti-matter experiments. Without magnetic containment, any anti-matter you create is worse than useless, as it will destroy your equipment. :slight_smile:

Well, the ability to repell/attract other magnets has to do with the direction (clockwise/counterclockwise) of the magnetic field. If you zoom in closely enough, it’s like having a bunch of tiny bar magnets arranged in a circle.


So it seems that I was right about the polarity of the molecules. It’s just that in a ring, there is no terminus to give a pole. Right?

There are more than one kind of “ring magnet.”

Some of these are disk magnets with the N and S poles being on the faces of the disk. Then drill a hole in the disk to convert it into a ring. The poles are still on the flat faces, and the magnets have strong attraction to iron and to other magnets. Radio Shack sells lots of these.

A permanent magnet with a closed ring-shaped field inside itself does not attract metal, so it has no real use, and you can’t buy such a thing as far as I know. The closest example is a pair of “C-shaped” horseshoe magnets. Place them together so the N and S poles are adjacent, and you create a donut magnet with a ring-shaped field inside, yet the field outside is nearly zero.

Hey, that’s what I was talking about!! I didn’t know that. In fact, I was just re-reading what I wrote before, and thinking that I’d have to point out that there must be some sort of polarity, or the “ring” magnets wouldn’t repel each other.

So that’s the explanation.

Ok…so energy cannot be created or destroyed…what happens when you force two powerful magnets together like-pole wise?
The field repel each other…aren’t you adding energy by pushing them towards each other? Where does that energy go? Does it create heat? Increase the power of the magnetic fields somehow?

I’ll also add that there is a limit to how strong a magnet can be. A piece of iron, say, is made up of a whole bunch of magnetic domains, each of which can be considered a little magnet. If the domains are all randomly oriented, then there’s no net magnetization, but if they’re predominantly oriented one way, then you have a magnet. The strongest you can get is if they’re all aligned the same way.

Magnets can lose their magnetism if mechanically stressed (for instance, by being dropped or being hit with a hammer) or if heated. Oddly, a non-magnetized piece of iron can also be magnetized by these same processes. An existing magnetic field helps, but isn’t necessary. Did you ever notice two of your butterknives sticking together, for instance? Cutlery often becomes spontaneously magnetized. You can also magnetize or demagnetize a hunk of iron by exposing it to a strong external field, without heat or stress.

As for monopoles, theorists are almost convinced that they should exist, but they’re predicted to be extremely rare. There should be approximately one monopole in the entire observable Universe. For most practical purposes, you can just say that they don’t exist.

Sirreal72, you’re right, you’re adding energy by pushing two magnets together that don’t want to do it. You’re sort of storing up the energy in the potential of the repelling fields.

When you finally let go, the “stored” energy will be converted into kinetic (moving) energy, and that will be used up in heating up the magnets and whatever they land on or scoot across. There’s no cheating the laws of physics; all the energy will be converted eventually to heat, this time just fairly quickly. You can tell when the conversion is complete, because that’s when the magnet will stop moving.