Magnets

[jtaunton]

My son has just been given a present of a dragon and a castle.

The castle has a metal plate near the top of it. The dragon is holding a magnet, and has chains around its legs. The magnet is attracted to the metal plate, but the chains hold it back, giving the effect of the dragon floating in mid-air.

Now I don't think that magnetism 'runs out', but it also seems wrong to me that if I put the dragon/castle in the loft and came back to it in 50 years, that the dragon would still be floating in mid-air.

Anyone like to hazard a guess as to what would happen ?

 

[kendor]

Depends on what type of magnet used, the super strong rare earth neodymium ones don't lose their strength unless they are damaged (they are brittle and don't like heat unless they are high temp ones like used in the oil drain plugs in engines) and don't need a retaining bar attached when not in use.
In fifty years time the dragon might still be floating but you may be lying underground

 

[nstreet]

You wouldn't be able to find it in the loft because 1, you would have forgotten you ever had it. 2 it would be buried under 50 years of other worthless junk that you had collected.

 

[jtaunton]

Ah, but you haven't taken into account the magic of eBay. There is a steady stream of long neglected Sisters of Mercy records leaving my loft and going to Germany, freeing up space for magnetic dragons and other experiments.....

 

[kendor]

Ah, but you haven't taken into account the magic of eBay. There is a steady stream of long neglected Sisters of Mercy records leaving my loft and going to Germany, freeing up space for magnetic dragons and other experiments.....

have you got something against germans then? still remembering the war are we

 

[jtaunton]

Anything that dilutes the percentage of David Hasselhoff records in the country has got to be an act of kindness, surely.....

 

[kendor]

Anything that dilutes the percentage of David Hasselhoff records in the country has got to be an act of kindness, surely.....

Ok let you off then

 

[securespark]

Anything that dilutes the percentage of David Hasselhoff records in the country has got to be an act of kindness, surely.....

What???? even if they're sisters of mercy??

 

[jtaunton]

Its when the Sisters of Mercy collection runs out that they should really be afraid.....

Anyway, back to the magnets - Assuming that it is not one of the super strong rare earth neodymium ones, where does the magnetism 'go'. Does it somehow dribble away through some sort of magnetic circuit, does it radiate, or does it just fade ? And why ?

 

[petewood]

The goblins come and steal the magnetism so the dragon can escape!

 

[kendor]

perhaps this explains it? perhaps not?
Extract from another forum,

Guest_solidspin 27th April 2005 - 03:05 PM

I think I can comment on this, since I sit underneath a supercon magnet all the time!

Why hasn't anyone mentioned the source of magnetism on a macroscopic level yet? Great natural magnets are so because they're very often high-spin d-orbital elements (Fe, Co, Ni) and all their spins in these d-orbitals are unpaired and parallel. They have what's called a permanent magnetic moment, because their spins (their magnetic moments) always sit there like that.

HOWEVER, a permanent magnet CAN temporarily lose its moment if you crank up the temp beyond what's called the Neel temp. for that material. What's interesting is that when the electrons settle back down from the higher, thermally induced excited states, they go back to their parallel magnetic moment state.

Oxygen (O2) is paramagnetic, for example, because of its 2 unpaired electrons in what chemists call a "pi-antibonding orbital" - whatever - the point is that the unpaired electrons are randomly oriented magnetic moments, since there's no solid crystal lattice or fixed orientation (it's a gas gas gas!). So you can make oxygen's electrons line up in a parallel state if you apply a field to them (it's old school but its called a Guoy balance).

I just gave a talk on SMMs or single molecular magnets. Just like a paperclip is not magnetic but can be induced to have a magnetic moment (like we all did to mom's paperclips with refrigerator magnets), a new class of funky molecules (some as large as a freakin' protein) only 1 molecule big can be induced to have a long magnetization (like over 40 minutes - that's sweet). Even cooler, and I think STe or the1physicist mentioned this, its rare but DEFINITELY possible to see macroscopic observables of quantum mechanical phenomena. These SMMs demagnetize or relax in a stepwise fashion (not like the classical hysteresis curve, which is analog), corresponding to tunneling of magnetization to antiparallel spin states. Totally cool!

The supercon magnets are niobium tin (YBCO is great too, but it's a ceramic and therefore not malleable). It's just Faraday's law applied to a Niobium Tin (in my case) metal, which as the1physicist will agree is a free-electron gas lining up in Foch space.

 

[felix]

For the benefit of non-physicists here is a Dummies' Guide to Magnets ---

The magnetism doesn't 'go' anywhere. An iron atom sitting in your loft is magnetic and will remain so until long after the loft has gone. What makes iron, nickel and cobalt different from other magnetic atoms (of which there are many) is that they will naturally line themselves up so that their magnetic fields add.

Most magnetic atoms prefer to lie 'head-to-tail' as it were so they cancel out. Hydrogen is a good example. A single atom is a magnet but the hydrogen molecule (two atoms) is not. If you could freeze single hydrogen atoms with their little magnets all aligned you would have (probably) the most ferocious magnet ever made outside of a neutron star. Don't quote me on this but such a magnet may lie in Jupiter's core.

Back to common old iron. The atoms line themselves up in little magnetic groups called domains. In a non-magnetized lump of iron these domains are all jumbled up so the overall magnetic field is zero. The trick is to align the domains. This can be done by rubbing the iron with another magnet, by hitting it within a magnetic field or, more likely, by putting it inside a beefy electromagnet and forcing them into line.

Once lined up they will stay that way unless you agitate them, eg by heating or bashing them too much. Over a very long period they will lose their alignment even at room temperature but I see no reason why a 50 year old magnet shouldn't have quite a lot of its original magnetism left.

Incidentally, I'm not sure that rare earth (neodymium-iron-boron or cobalt-samarium) magnets existed 50 years ago. The best magnets around in the sixties seemed to be aluminium-nickel-cobalt (alnico). Maybe somebody else out there knows different.

 

[Thermo]

the magnets down our way are really good. they sell doors windows and allsorts

 

[pipme]

Bristol once had a 'Magnet Bowling Alley' quite an attractive place.

Mate once had an MG Magnet car .... Similar car but not the M8 .. no flares !!

 

[jtaunton]

My friend used to have a Dragon 32........

I was too busy messing about with my MSX though.