This episode was made possible by generous supporters on Patreon. Hey Crazies. In the previous video, we learned what
electric charge really was: A measure of how much something can
affect the electric field. So the next logical question is: Does the magnetic field work the same way? Is there some kind of magnetic charge that
affects the magnetic field? That would be nice, but it’s a little more
complicated than that. No, the magnetic field is affected by the
same thing as the electric field: electric charge. This proton has a positive electric charge. If it’s sitting still, then only the electric field is affected. But if it moves, it can also affect the magnetic field. The orange Xs and dots represent direction
into and out of your screen because that’s what a simple arrow would
look like in each of those cases. We can see the moving proton affects both
fields. Historically though, we don’t do experiments
with single charged particles. So, while this diagram is accurate,
it’s not very practical. We usually have a bunch of charges moving
together in something we call a current. To the timeline! In 1819, Hans Christian Ørsted noticed that
magnetic compasses deflected near a current-carrying wire. Kind of like this. On. Off. On. Off. On. Off. Then in 1820, Jean-Baptiste Biot and Félix
Savart found a simple pattern for this. But then Pierre-Simon Laplace almost immediately generalized it because, you know, mathematicians are like that. Side Note! Laplace was a BAMF! Seriously! He was, like, 70 by the time he did this. To honor Laplace for his hard work, we named
his law: Laplace’s Law. Just kidding! It’s called the Biot-Savart Law. What?!?!?! His name isn’t even on it?! Yeah, I know. It totally sucks, but, in all fairness,
the man has plenty of stuff named after him. He doesn’t really need it. Even electrodynamics, the topic of this series,
has a Laplace’s equation. He did a lot of stuff in his life. End of side note! The point is magnetism appears when charge moves. It doesn’t matter if it’s a single charge or a whole bunch of charges moving through a long wire. It doesn’t even matter how that wire is shaped. Moving charge affects the magnetic field. Sure, that’s true for electromagnets, but
that doesn’t really explain this. Are you really going to make me go there? Yes, the crazies are going to like it. Ok, I can do this. We have what seem to be two different kinds of magnets. An electromagnet and what we call a permanent magnet. But, in the end, we’ll see both types of
magnets are really caused by the same thing. Let’s start with the names. An electromagnet is magnet created by electricity. There isn’t any electric current running
through a magnet like this though, so it seemed like it should go by a different name. We went with permanent magnet, because we
thought they lasted forever. Over time though, they can lose their magnetism,
especially if they get hot. But, left to their own devices, that process
could easily take thousands of years. Compared to a human life span, that still
seems like forever. Anyway, it’s the name we’re stuck with. Now for the basic properties. Based on the shape of the magnetic field,
we notice there are two opposite sources. We call these sources poles and label them
north and south. Why we use those labels has to do with the
Earth’s magnetic field, but that’s a topic for another day. All permanent magnets have at least one north
pole and one south pole. Even electromagnets have poles if they’re
shaped certain ways. Sometimes magnets have more than one set of poles, but they always come in pairs. Always! It’s a behavior summed up pretty well with
Gauss’s law for magnetism. So how is a piece of material magnetic if
there’s no electric current? Quantum mechanics. Hold onto your butts. To understand how something like this can
be a magnet, we need to look closer... ...a lot closer. Super zoom! This is what a chunk of iron looks like on
a molecular level. Yet, we still don’t see any moving charges. For that, we have to zoom in one more step. This cloud of negative charge is made of 26 electrons. Each of those electrons is in something called an orbital. Those come in a variety of shapes, each with a set of available properties. But we need to be careful. Quantum particles can have all sorts of properties: position, energy, linear momentum, angular momentum. All the properties! The property the electrons have in these orbitals
is angular momentum. In fact, we can measure both the total amount
and the orientation, at least along one direction. Just having that property is enough to make
it a tiny magnet. Any electron with a non-zero angular momentum
will act like a tiny magnet. Unfortunately, that doesn’t necessarily
turn the entire iron atom into a magnet because electrons tend to pair up in opposite directions. There 26 electrons in an iron atom. For each one that’s in a clockwise orbital, there’s another one that’s in a counterclockwise orbital. They cancel each other out, so this level of existence isn’t deep enough. We need to zoom in even closer. This single electron has an inherent property
called spin angular momentum. That’s something I’ve talked a lot about in this video. It’s not really a motion, but it is momentum
and that’s enough for magnetism. When you zoom back out to the atomic level,
most of those electrons still pair up and cancel, except four of them. Because like charges repel, they get as far
from each other as possible and line up in the same direction, at least
in iron. The more of those loner electrons an atom
has lined up, the more magnetic it’s going to be. That tends to happen in the middle of blocks
on the periodic table. But, just because an atom is magnetic, it doesn’t necessarily mean the material is magnetic. Don’t ever jump to conclusions in quantum mechanics. Getting the loner electrons to line up isn’t enough. You also have to get nearby atoms to line
up with each other and then get enough regions of atoms to line
up. We call those regions domains. The point is magnetic materials are hard to come by. In fact, there are only four elements that
do this at room temperature: Iron, Cobalt, Nickel, and Gadolinium. Beyond that, we either need to get the material really cold or build the material using a specially-designed molecule or both. So, what the heck is a magnet? Magnets are what you get when charges move
or at least have momentum. That’s true if you’re talking about a
single charge, a bunch of charges in a current, or even the spin of subatomic charges in a piece of iron. All magnets come from charges,
so all magnets are electromagnets. Wicked, huh? So, how fascinated are you by magnets? Let us know in the comments. Thanks for liking and sharing this video. Don’t forget to subscribe if you’d like
to keep up with us. And until next time, remember, it’s OK to
be a little crazy. In the last video, a big question was: Why do the particles have the specific charges that they do? Well, we don’t know. Those charges have to be measured and then
put into the standard model. We haven’t found an underlying mechanism, yet. Anyway, thanks for watching!
