What the HECK are Magnets? (Electrodynamics)

Summary

This educational video explores the relationship between electric charge and magnetic fields, debunking the myth of magnetic charge and explaining how moving electric charges create magnetic fields. It delves into the historical discovery by Hans Christian Ørsted and the subsequent Biot-Savart Law. The video also distinguishes between electromagnets and permanent magnets, linking their magnetic properties to moving charges and electron spin angular momentum. It concludes with a fascinating look at the quantum mechanics behind magnetism in materials like iron, cobalt, nickel, and gadolinium.

Takeaways

• 🔋 Electric charge is a measure of how much something can affect the electric field.
• 🧲 Unlike electric fields, magnetic fields are not affected by a separate 'magnetic charge' but by moving electric charges.
• 🚀 The movement of a charged particle, like a proton, can influence both electric and magnetic fields.
• 🌐 In 1819, Hans Christian Ørsted discovered that electric currents could affect magnetic compasses, demonstrating a link between electricity and magnetism.
• 🤔 The Biot-Savart Law, not Laplace's Law, describes the pattern of how a current-carrying wire affects a magnetic field.
• 🔗 Magnetism arises from moving charges, whether it's a single charge or many charges in a current.
• 🧭 Permanent magnets and electromagnets are fundamentally caused by the same principle: the movement or momentum of charges.
• 🌐 The Earth's magnetic field plays a role in why we label magnetic poles as north and south.
• ⚛️ Atoms can exhibit magnetism due to the spin angular momentum of unpaired electrons, particularly in elements like iron, cobalt, nickel, and gadolinium.
• 🤷‍♂️ Despite extensive study, the specific charges of particles remain a mystery, needing to be measured and incorporated into the standard model without a known underlying mechanism.

Q & A

What is the relationship between electric charge and electric fields?

Electric charge is a measure of how much something can affect the electric field.

Does a magnetic charge exist that affects the magnetic field in the same way electric charge affects the electric field?

No, the magnetic field is affected by electric charges, not by a separate magnetic charge.

How does a moving electric charge affect the magnetic field?

A moving electric charge can affect the magnetic field, as demonstrated by a proton that, when moving, can influence both the electric and magnetic fields.

What did Hans Christian Ørsted discover in 1819 regarding magnetic fields and electric currents?

Hans Christian Ørsted discovered that magnetic compasses would deflect when placed near a current-carrying wire.

Who formulated the Biot-Savart Law and what does it describe?

The Biot-Savart Law was formulated by Jean-Baptiste Biot and Félix Savart. It describes the pattern of how a current-carrying wire affects the magnetic field.

What is the difference between an electromagnet and a permanent magnet?

An electromagnet is created by electricity and has an electric current running through it, while a permanent magnet does not have a current running through it and retains its magnetism for a long time without an external power source.

Why do all permanent magnets have at least one north pole and one south pole?

This is due to the basic properties of magnetic fields, which have two opposite sources that are labeled as north and south poles.

What is the role of quantum mechanics in explaining the magnetism of materials?

Quantum mechanics is essential for understanding magnetism at the atomic and subatomic levels, particularly in explaining how electrons' angular momentum and spin contribute to magnetism.

How do the electrons in an iron atom contribute to its magnetism?

In iron, four of the electrons have unpaired spins that line up in the same direction, contributing to the atom's magnetism.

What are the four elements that exhibit magnetism at room temperature?

The four elements that exhibit magnetism at room temperature are Iron, Cobalt, Nickel, and Gadolinium.

What is the significance of domains in the context of magnetic materials?

Domains are regions within magnetic materials where atoms with aligned magnetic moments are grouped together, which is necessary for the material to exhibit macroscopic magnetism.

Outlines

00:00

🔋 Understanding Electric and Magnetic Fields

This paragraph introduces the topic of electric and magnetic fields, emphasizing the role of electric charge in affecting both. It explains that while a stationary charge only influences the electric field, a moving charge can also impact the magnetic field. The historical discovery by Hans Christian Ørsted that a current-carrying wire can deflect a magnetic compass is mentioned, leading to the Biot-Savart Law, which describes the pattern of magnetic fields around a current. The paragraph also touches on the concept of electromagnets and permanent magnets, suggesting that both are fundamentally caused by moving charges, despite the latter appearing to lack an electric current. The discussion concludes with an introduction to the quantum mechanical explanation of magnetism, hinting at the role of electron angular momentum and orbitals within atoms.

05:02

🌀 Deep Dive into Magnetism and Quantum Mechanics

The second paragraph delves deeper into the quantum mechanical basis of magnetism, focusing on the behavior of electrons within atoms. It explains that while most electrons pair up and cancel out their magnetic effects due to opposite angular momentum, a few 'loner' electrons can align in the same direction, contributing to an atom's magnetic properties. The paragraph highlights the importance of these unpaired electrons in creating magnetic domains within materials, which are necessary for a material to exhibit magnetism. It mentions that only a few elements, such as iron, cobalt, nickel, and gadolinium, naturally form magnetic domains at room temperature. The summary also points out the broader concept that all magnets, whether from moving charges in a current or the intrinsic spin of subatomic particles, are fundamentally electromagnets due to the involvement of charges.

Keywords

💡Electric charge

Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. In the video, it is described as a measure of how much something can affect the electric field. The concept is foundational to understanding electromagnetism, as it is the electric charge that influences both electric and magnetic fields, especially when in motion.

💡Magnetic field

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. The video explains that, unlike electric fields which are directly caused by electric charges, magnetic fields are affected by moving electric charges. This is a key distinction that leads to the exploration of how magnets and electromagnets function.

💡Electric current

Electric current is the flow of electric charge. It is typically measured in amperes. In the context of the video, electric current is what causes a magnetic field when charges move together, such as in a wire. The historical experiment by Hans Christian Ørsted, where a magnetic compass deflected near a current-carrying wire, is a classic demonstration of this concept.

💡Biot-Savart Law

The Biot-Savart Law describes the magnetic field generated by a steady electric current. It is a fundamental principle in electromagnetism that helps calculate the magnetic field around a current-carrying wire. The video humorously notes the law's naming, which honors Biot and Savart, despite Laplace's significant contributions to its generalization.

💡Permanent magnet

A permanent magnet is a material that is magnetized, creating a persistent magnetic field. The video discusses how these magnets were named due to their long-lasting magnetic properties, which can endure for thousands of years without significant loss of magnetism, although they are not truly permanent.

💡Electromagnet

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The video explains that all magnets, including permanent magnets, are fundamentally electromagnets because they involve moving charges or charges with momentum, even at the subatomic level.

💡Magnetic poles

Magnetic poles are the two opposite ends of a magnet where its magnetic field is the strongest. The video mentions that all magnets have at least one north pole and one south pole, and these are crucial for the magnetic properties of materials, including their interaction with the Earth's magnetic field.

💡Quantum mechanics

Quantum mechanics is the branch of physics that deals with the behavior of particles at the atomic and subatomic level. The video delves into quantum mechanics to explain how materials like iron can become magnetic at the molecular level, involving concepts like electron spin and angular momentum.

💡Angular momentum

Angular momentum is the rotational equivalent of linear momentum and is a fundamental property of particles in quantum mechanics. In the video, it is explained that electrons with non-zero angular momentum act like tiny magnets, which is essential for understanding the magnetic properties of materials at the atomic level.

💡Magnetic domains

Magnetic domains are regions within a magnetic material where the magnetic moments are aligned. The video explains that for a material to exhibit magnetism, not only do individual atoms need to have aligned electrons, but these atoms must also align with each other across domains to create a net magnetic field.

Highlights

Electric charge is a measure of how much something can affect the electric field.

Magnetic fields are affected by electric charges, not a separate magnetic charge.

A moving proton can affect both electric and magnetic fields.

Historically, experiments with magnetic fields involve currents, not single particles.

Hans Christian Ørsted discovered that electric currents can affect magnetic compasses.

Biot-Savart Law describes the pattern of magnetic fields around current-carrying wires.

Magnetism arises from moving charges, regardless of whether they are in a wire or a magnet.

Permanent magnets are named for their long-lasting magnetism, which can degrade over thousands of years.

Magnetic fields have two opposite sources called poles, labeled north and south.

Gauss’s law for magnetism states that magnetic poles always come in pairs.

Magnetism in materials without electric current is explained by quantum mechanics.

Electrons with non-zero angular momentum in orbitals can act as tiny magnets.

In iron atoms, four electrons with unpaired spins contribute to the material's magnetism.

Magnetic materials require alignment of unpaired electrons and their atomic domains.

Only four elements are magnetic at room temperature: Iron, Cobalt, Nickel, and Gadolinium.

All magnets, including permanent magnets, are fundamentally caused by moving or momentum-carrying charges.

Magnetism is a fascinating phenomenon that arises from the behavior of subatomic particles.

Transcripts

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!