Magnet je látka, uvnitř které se nachází pohyblivé elektrické náboje. Tyto náboje svým pohybem vytváří elektrické proudy. Pohyb těchto částic ovlivňuje i své okolí. Vytváří něco jako vír. Takto aktivní okolí nazýváme magnetickým polem.

Magnetické pole snadno znázorníme střelkou z kompasu. Ta je totiž lehounká, snadno se okolním prostředím zmagnetizuje a může se volně pohybovat. Ukáže nám tak, kudy směřují magnetické proudy. Všimněme si rozdílu uvnitř magnetu a v jeho okolí. Písmenka N a S znamenají „North“ – sever a „South“ – jih. Mají za úkol odlišit magnetické póly.

2 minuty o magnetu

Přepis:

Magnets can be created by running currents through wires, finding a suitable material
that naturally has all the magnetic fields of its atoms aligned, or forcing the magnetic fields of atoms to align.

But there’s one more kind of magnetism that all materials exhibit, even those whose constituent atoms aren’t magnetic – though it’s so weak that the other kinds of magnetism often overwhelm it. Basically, an external magnetic field causes the electrons around atoms in a material to change course, and their new motion generates an opposing magnetic field. This field is pretty weak, but it does cause the material to be repulsed from the magnet a little bit – for example, if you hang a wooden toothpick in a magnetic field, the ends will repel the field and it will end up aligning across the magnetic field.

This is a convenient way to remember the name of this kind of magnetism – diamagnetism – since „dia“ means across, like the „diameter“ measured across a circle. Diamagnetic materials will repel a magnet, and a diamagnetic „compass“ will point across the magnetic field – that is, it will orient east/west.
As weak as it is, diamagnetism is pretty darn awesome because it’s a repulsive effect: any diamagnetic material will levitate in a strong enough magnetic field! Like this chunk of graphene, or, since water is diamagnetic, this frog. In principle, humans could also be levitated this way, though the magnetic fields required would be enormous.

There are also a lot of subtleties we’ve skated over, like the fact that nitrogen is diamagnetic even though as an atom it has unpaired electrons – one might think that it *should* be at the very least paramagnetic. But nitrogen atoms bond to form N2 molecules which have full outer electron shells and are thus only diamagnetic. On the other hand, molecular O₂, as we’ve seen, still has unpaired electrons, and it’s paramagnetic.

You’ve probably also seen how superconductors can levitate in a magnetic field, which is a kind of perfect diamagnetism – not only do the currents in a superconductor create opposing magnetic fields, they expel magnetic fields from the material entirely. But the root cause is very very different, and that’s a journey for another day.

Slovník:

current	obvod	wire	drát	field	pole
motion	pohyb	levitate	vznášet se	shell	vrstva
superconductor	supravodič