ELI5; How exactly do magnets pull other objects? Like, what exactly are North and South poles and what causes them? How do aligned iron atoms affect other objects and pull on electrons in wires?


ELI5; How exactly do magnets pull other objects? Like, what exactly are North and South poles and what causes them? How do aligned iron atoms affect other objects and pull on electrons in wires?

In: 14

They just do. Really. Magnetism isn’t the question, it’s the ultimate answer to everything. The electro-magnetic force is one of the fundamental forces of the universe at the bottom of how everything works. To tear it apart so you can see it’s inner workings is beyond ELIF. It’s like how does gravity pull you to the ground? It just does.

There is a quantum electromagnetic field that permeates all of spacetime. When you energize a magnetic field, perhaps by switching on an electromagnet or perhaps by putting a permanent magnet into a place in space, you add magnetic flux into this field. Magnetic flux is sorta† like an electric current, but it flows in the field itself, rather than just through a wire. Electrons moving in the field feel a force from their interaction with the resulting magnetic field. If the electrons are moving through a wire, the wire feels the force. If the electrons are in a permanent magnet, the magnet feels the force. That’s the force that pushes two magnets together/apart.

† This is a rather extreme simplification. Electromagnetism is best described in equations, but that’s the antithesis of ELI5.

Charged objects that move make magnetic fields. Electrons are charged, so when they move, they make a magnetic field. The thing about electrons though is that they are always moving, so each electron always has a magnetic field. Magnetic fields have a direction to them – when they line up the same way they add together, when they line up opposite the cancel out, and when they are at 90 degrees from each other nothing happens.

Generally, electrons are disorganized and their magnetic fields point in every direction, so they all cancel out. When you have a whole bunch of electrons aligned the right way, all of their tiny magnetic fields add together to make one big magnetic field. When the magnetic field is big enough, magnetic forces become strong enough to beat out other forces like friction or gravity that keep the object still.

It’s hard to do ELI5, but your question on the other response (why do iron atoms align like that) has a fairly simple response. Earth generates its own magnetic field. When magnetic rocks (see lodestone) are being “made,” they are really hot. This allows the atoms to orient themselves in whatever way they want. Since they are in earth’s magnetic field, and they were partially composed of the right element (iron), they orient themselves along earth’s magnetic field lines. Then they cool and these orientations get locked in. That’s how some other permanent magnets are made by people, too. Heat up the material, apply a strong magnetic field, and cool.

Why iron in the first place? That is pretty hard to answer. You’ll have to accept that it’s an intrinsic property of iron due to some interactions between electrons from neighboring atoms inside the piece of iron. Look up the “exchange interaction” if you want to read more about that. North and South poles are just the names given to the sides of a magnet, derived from using lodestones as compasses. Magnetic field lines will always point from north to south outside a magnet, and south to north inside, to form closed loops. The closed loop part is again dicey to explain here, but it’s one of Maxwell’s equations (no magnetic monopoles), and very fundamental to physics. Because of this, you always have a dipole (two poles), and we’ve named them north and south.

“How do aligned iron atoms affect other objects and pull on electrons in wires.” When you bring two magnetic fields together, they will interact; a north pole will attract a south pole and repel a north pole. Electrons have charge, which means they have an electric field. Another one of Maxwell’s equations shows that a moving electric field generates a magnetic field. Actually, it was found accidentally that electric currents produced a magnetic field in the opposite of your scenario. Hans Christian Oersted had a compass lying around when he was doing experiments with electricity, and noticed his compass was spinning around and aligning whenever current was flowing through the wire, haha.

What causes magnetism? There is really two mechanisms behind this, both having to do with the electrons in the material. One is much easier to understand, the other contributes more. Suffice the one to say it has to do with an electron’s “spin,” which is a quantum mechanical type of angular momentum. The contribution that is way easier to understand is the electron’s orbit around the nucleus. Well, remember above when I said moving electric fields create magnetic fields? It doesn’t have to just be a current through a wire; the motion of a single electron around a nucleus creates a very weak magnetic field. But, importantly, in these materials we’ve already established that during formation the magnetic moments were all aligned by the external field as they cooled. So even though individually these “current loops” formed by electrons are weak (and normally, cancel eachother out when randomly oriented), when they are all aligned they actually add up to something quite substantial. Same thing for the spin-related portion of the magnetic field.

There’s a few other ways magnets will interact with other materials. Ferrimagnetism is all what we were talking about with iron as above, the atoms all get aligned when the magnet is created with an applied external magnetic field. There’s also paramagnetism, which is when some objects aren’t inherently magnetic, but very weakly attracted to them. These aren’t magnetic on their own but will be pulled slightly by an external magnet. Then there is diamagnetism, which is the opposite. They aren’t magnetic on their own, but are weakly repulsed by magnetic fields. In these materials, magnetic fields are “induced” within them by the external magnet, and if this induced field is opposite to the applied field, the material is diamagnetic, and if it is in the same direction it is paramagnetic.

Follow up question, hover boards?