HOW DO MAGNETS WORK?

Physics and writing provided by Nils Mulder.

 

We have all come across magnets, whether it is from simple refrigerator magnets, to train sets we played with as kids, or even ultra-powerful magnets from access-restricted physics labs. When we released the Magination GIFs on the internet, the response was enormous, and the most frequently asked questions was “How do they work?”*

*Yes, usually in reference to Insane Clown Posse’s well-known song “Miracles”.

This seems like a straightforward question to answer, but to come up with a simple and sophisticated answer without spewing out too much hardcore physics seems tough. Why? Well, magnets are complicated.

Magnetism is a property that not all materials possess. To understand why, we have to dive deep into some physics – but don’t worry! We’ll keep it relatively simple. For starters it’s good to know that magnetism is closely related to electricity; they are like close buddies who enjoy being in each other’s presence.

Back in the year 1831, English scientist Michael Faraday conducted a world famous experiment to show that magnetism and electricity are in fact related. He did this by leading a bar magnet through a looped copper wire which was connected to a Galvanometer (a sensitive current-measuring device). The motion of the bar magnet made the Galvanometer react – a current was going through the wire! So the motion of the magnet near the copper wire induced a current!

* The image does not show the experiment actually looked like back in 1831! 

In fact, it was also discovered that moving charges (like electrons) induce a magnetic field! So it works both ways.

At the time, there was no broad interest in this phenomenon; at the very best it was a cool party trick. Make the needle on the galvanometer jump by moving a magnet close to it. Yey! It is even said that the Prime Minister at the time asked Faraday about his discovery and what it was good for, upon which Faraday replied; “Sir, what good is a newborn child?”. His point is that you don’t know if your child, or for this sake the relationship between electricity and magnetism, will grow up to do something huge. In this case, huge is an understatement. Because of this relationship we have electricity to keep our food cold, our water hot and our computers online. As a matter of fact, you probably wouldn’t have any of the things you see around you today, if it wasn’t for this startling discovery!

So, electricity and magnetism are related. Now what?

To understand why some materials are magnetic and some not, we have to look closer at how materials are built up. Everything around us is built up by atoms. In the simplified version, all atoms contain a positively charged nucleus (consisting of protons and neutrons) and negatively charged electrons orbiting the nucleus. In this simplified view, you can think of the electrons as the planets orbiting the sun, which here is represented by the nucleus. The electrons orbit the nucleus at different distances – just like the planets!

As we now know from Faraday’s discovery, magnetic fields arise from charge in motion – and this is exactly what the electrons are. As they orbit the nucleus they induce a magnetic field!

In addition, the electrons have a property called spin. It would be tempting to explain the spin of electrons as the spin the Earth has around its own axis. This is because the Earth’s spin gives rise to a magnetic field (the Earth consists of a bunch of charges), and this is also what electron spin does. The similarities however, stop there. The electrons only act like they’re spinning very, very quickly, thus producing a magnetic field. In addition, electrons have spin up or spin down (counteracting directions). Why they only act like they’re spinning very fast is more thoroughly explained by quantum mechanics (the physical laws for things that are smaller than about 100 nanometers, where all sorts of craziness happens), but we’ll leave that one alone. Why? Well, an electron isn’t really a particle with well defined radius or volume; it is more like a point in space, and therefore it doesn’t have an axis to spin around. But if it could in fact spin, the measured magnetic field that is produced by this motion is so big that the electrons would have to spin faster than the speed of light, which Einstein and about a zillion others (small overstatement) proved to be impossible. Let’s not go deeper into the woods here.

The take away message is that an electron’s spin gives rise to a magnetic field, and this property is called spin because it’s kind of (but not at all) like, the Earth’s spin around its own axis.

Okay, so atoms with electrons that act like they spin create a magnetic field, but why isn’t everything magnetic then? In most cases, the net magnetic field is cancelled out because the atoms contain equal amounts of electrons with spin up and spin down. When they don’t, the result is a charge in some direction, and the atoms are magnetic!       
Having a bunch of magnetic atoms isn’t necessarily enough to be magnetic, as the atoms have to align their magnetic fields as well. When they do, the material is “ferromagnetic”. The only common ferromagnetic materials in room temperature are iron, cobalt and nickel. Within these materials we find “domains”, which are clusters of atoms aligned the same way. If all these domains point in different directions, even they can cancel each other out! With a strong external magnetic field, you can force these domains to align, creating a magnet!

A magnet has a north pole and a south pole. Equal poles repel each other, while opposite poles attract each other (you have probably experienced this already). The poles are places where the magnetic field is concentrated and either leave, or go into the magnet. By convention, the place where the magnetic field leaves the material is called the north pole, and the place the field come into the material is called the south pole. You might be surprised to hear that the geographical North Pole is basically the same as the magnetic south pole. In fact, the north pole on a compass points towards the magnetic south pole, not the North Pole! A cool thing about the magnetic field is that it has no specific point of origin. It just goes in loops between the north pole and the south pole and through the magnet again.

The thing to understand is that magnetic poles always show up in pairs – never alone. They’re kind of like an annoying couple who never have time to be with their friends unless they come together. There are theories about magnetic monopoles, but these have never been confirmed experimentally. So if you one day decide to cut a magnet in half, you would end up with two magnets (the metaphor about couples ends here – do not try to cut them in half to see if they’re still a couple). Want to see it for yourself? Stack some Single pieces – the stack will have one north and one south pole altogether, and act as “one magnet”. Now split the stack in half and you’ll have two magnets – each one with a north and a south pole!

In one of our GIFs we played magTension. When you put a lot of individual magnets close to each other in a confined space, crazy things may happen. At a certain point, the repelling fields will be so strong, that the slightest change in it will cause a strong repulsive force on its neighbour – which might flip over.

 

 

This will disturb the magnetic fields of the magnets next to it – which suddenly will be attracted by the flipped Single piece. They will hurry towards it, and in the flustercluck of changing magnetic fields, they might align and smack together into a smooth looking magnetic bar.

You now know a little more about magnets! Go dazzle your friends with your magtastic skills and knowledge!

We have only scratched the surface of what humanity knows about magnetism in this manual. Hopefully, we have tickled your curiosity. There are still many mysteries out there that have yet to be discovered. How are particles like electrons are charged in the first place? Nobody actually knows this. Yet. That’s what makes magnetism and science so exciting. There are theories and experiments being conducted and tested every day. Who knows what the future will bring? We don’t know that either, but you can be a part of it!

TL;DR too long; didn’t read:
A magnetic field comes from a magnet. A magnet consists of many small magnets aligned in the same direction.