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We've learned a little
bit about gravity.

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We've learned a little bit
about electrostatic.

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So, time to learn about
a new fundamental

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force of the universe.

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And this one is probably second
most familiar to us,

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next to gravity.

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And that's magnetism.

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Where does the word come from?

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Well, I think several
civilizations-- I'm no

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historian-- found these
lodestones, these objects that

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would attract other objects
like it, other magnets.

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Or would even attract metallic
objects like iron.

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Ferrous objects.

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And they're called lodestones.

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That's, I guess, the Western
term for it.

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And the reason why they're
called magnets is because

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they're named after lodestones
that were found near the Greek

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province of Magnesia.

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And I actually think the people
who lived there were

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called Magnetes.

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But anyway, you could Wikipedia
that and learn more

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about it than I know.

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But anyway let's focus
on what magnetism is.

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And I think most of us have at
least a working knowledge of

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what it is; we've all played
with magnets and we've dealt

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with compasses.

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But I'll tell you this right
now, what it really is, is

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pretty deep.

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And I think it's fairly-- I
don't think anyone has-- we

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can mathematically understand
it and manipulate it and see

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how it relates to electricity.

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We actually will show you the
electrostatic force and the

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magnetic force are actually the
same thing, just viewed

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from different frames
of reference.

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I know that all of
that sounds very

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complicated and all of that.

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But in our classical Newtonian
world we treat them as two

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different forces.

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But what I'm saying is although
we're kind of used to

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a magnet just like we're used to
gravity, just like gravity

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is also fairly mysterious when
you really think about what it

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is, so is magnetism.

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So with that said, let's at
least try to get some working

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knowledge of how we can
deal with magnetism.

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So we're all familiar
with a magnet.

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I didn't want it to be yellow.

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I could make the boundary
yellow.

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No, I didn't want it to
be like that either.

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So if this is a magnet,
we know that a magnet

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always has two poles.

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It has a north pole
and a south pole.

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And these were just labeled
by convention.

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Because when people first
discovered these lodestones,

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or they took a lodestone and
they magnetized a needle with

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that lodestone, and then that
needle they put on a cork in a

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bucket of water, and that needle
would point to the

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Earth's north pole.

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They said, oh, well the side of
the needle that is pointing

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to the Earth's north, let's
call that the north pole.

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And the point of the needle
that's pointing to the south

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pole-- sorry, the point of the
needle that's pointing to the

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Earth's geographic
south, we'll call

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that the south pole.

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Or another way to put it,
if we have a magnet, the

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direction of the magnet or the
side of the magnet that

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orients itself-- if it's allowed
to orient freely

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without friction-- towards our
geographic north, we call that

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the north pole.

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And the other side is
the south pole.

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And this is actually a little
bit-- obviously we call the

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top of the Earth
the north pole.

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You know, this is
the north pole.

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And we call this
the south pole.

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And there's another notion
of magnetic north.

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And that's where-- I guess, you
could kind of say-- that

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is where a compass, the
north point of a

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compass, will point to.

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And actually, magnetic north
moves around because we have

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all of this moving fluid
inside of the earth.

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And a bunch of other
interactions.

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It's a very complex
interaction.

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But magnetic north is actually
roughly in northern Canada.

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So magnetic north
might be here.

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So that might be
magnetic north.

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And magnetic south, I don't know
exactly where that is.

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But it can kind of move
around a little bit.

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It's not in the same place.

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So it's a little bit off the
axis of the geographic north

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pole and the south pole.

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And this is another slightly
confusing thing.

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Magnetic north is the geographic
location, where the

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north pole of a magnet
will point to.

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But that would actually be the
south pole, if you viewed the

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Earth as a magnet.

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So if the Earth was a big
magnet, you would actually

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view that as a south
pole of the magnet.

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And the geographic
south pole is the

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north pole of the magnet.

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You could read more about that
on Wikipedia, I know it's a

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little bit confusing.

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But in general, when most
people refer to magnetic

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north, or the north pole,
they're talking about the

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geographic north area.

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And the south pole is the
geographic south area.

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But the reason why I make this
distinction is because we know

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when we deal with magnets,
just like electricity, or

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electrostatics-- but I'll show
a key difference very

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shortly-- is that opposite
poles attract.

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So if this side of my magnet is
attracted to Earth's north

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pole then Earth's north pole--
or Earth's magnetic north--

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actually must be the south
pole of that magnet.

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And vice versa.

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The south pole of my magnet here
is going to be attracted

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to Earth's magnetic south.

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Which is actually the
north pole of the

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magnet we call Earth.

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Anyway, I'll take Earth out of
the equation because it gets a

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little bit confusing.

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And we'll just stick to bars
because that tends to be a

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little bit more consistent.

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Let me erase this.

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There you go.

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I'll erase my Magnesia.

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I wonder if the element
magnesium was first discovered

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in Magnesia, as well.

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Probably.

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And I actually looked
up Milk of

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Magnesia, which is a laxative.

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And it was not discovered
in Magnesia, but it has

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magnesium in it.

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So I guess its roots could be
in Magnesia if magnesium was

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discovered in Magnesia.

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Anyway, enough about Magnesia.

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Back to the magnets.

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So if this is a magnet, and let
me draw another magnet.

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Actually, let me erase
all of this.

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All right.

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So let me draw two
more magnets.

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We know from experimentation
when we were all kids, this is

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the north pole, this
is the south pole.

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That the north pole is going to
be attracted to the south

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pole of another magnet.

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And that if I were to flip this
magnet around, it would

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actually repel north-- two north
facing magnets would

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repel each other.

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And so we have this notion,
just like we had in

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electrostatics, that a magnet
generates a field.

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It generates these vectors
around it, that if you put

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something in that field that can
be affected by it, it'll

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be some net force
acting on it.

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So actually, before I go into
magnetic field, I actually

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want to make one huge
distinction between magnetism

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and electrostatics.

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Magnetism always comes in
the form of a dipole.

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What does a dipole mean?

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It means that we
have two poles.

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A north and a south.

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In electrostatics, you
do have two charges.

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You have a positive charge
and a negative charge.

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So you do have two charges.

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But they could be
by themselves.

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You could just have a proton.

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You don't have to have
an electron there

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right next to it.

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You could just have a proton and
it would create a positive

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electrostatic field.

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And our field lines are
what a positive point

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charge would do.

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And it would be repelled.

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So you don't always have to have
a negative charge there.

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Similarly you could just
have an electron.

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And you don't have to
have a proton there.

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So you could have monopoles.

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These are called monopoles, when
you just have one charge

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when you're talking about
electrostatics.

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But with magnetism you
always have a dipole.

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If I were to take this magnet,
this one right here, and if I

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were to cut it in half, somehow
miraculously each of

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those halves of that
magnet will turn

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into two more magnets.

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Where this will be the south,
this'll be the north, this'll

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be the south, this will
be the north.

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And actually, theoretically,
I've read-- my own abilities

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don't go this far-- there could
be such a thing as a

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magnetic monopole, although
it has not been

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observed yet in nature.

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So everything we've seen in
nature has been a dipole.

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So you could just keep cutting
this up, all the way down to

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if it's just one
electron left.

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And it actually turns out that
even one electron is still a

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magnetic dipole.

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It still is generating, it still
has a north pole and a

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south pole.

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And actually it turns out, all
magnets, the magnetic field is

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actually generated by the
electrons within it.

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By the spin of electrons and
that-- you know, when we talk

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about electron spin we
imagine some little

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ball of charge spinning.

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But electrons are-- you
know, it's hard to--

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they do have mass.

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But it starts to get
fuzzy whether they

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are energy or mass.

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And then how does a ball
of energy spin?

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Et cetera, et cetera.

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So it gets very almost
metaphysical.

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So I don't want to go
too far into it.

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And frankly, I don't think you
really can get an intuition.

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It is almost-- it is a
realm that we don't

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normally operate in.

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But even these large magnets
you deal with, the magnetic

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field is generated by the
electron spins inside of it

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and by the actual magnetic
fields generated by the

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electron motion around
the protons.

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Well, I hope I'm not
overwhelming you.

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And you might say, well, how
come sometimes a metal bar can

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be magnetized and sometimes
it won't be?

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Well, when all of the electrons
are doing random

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different things in a metal bar,
then it's not magnetized.

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Because the magnetic spins, or
the magnetism created by the

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electrons are all canceling
each other out,

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because it's random.

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But if you align the spins of
the electrons, and if you

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align their rotations, then you
will have a magnetically

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charged bar.

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But anyway, I'm past the
ten-minute mark, but hopefully

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that gives you a little bit
of a working knowledge of

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what a magnet is.

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And in the next video, I will
show what the effect is.

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Well, one, I'll explain how we
think about a magnetic field.

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And then what the effect
of a magnetic

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field is on an electron.

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Or not an electron, on
a moving charge.

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See you in the next video.

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