Other Lessons in This Course
Thanks to science (and the Internet), we know that magnets aren't made of fairy dust, magic, or love. But what are magnets made of, and why do they work the way they do? What's inside those promotional magnets all over your refrigerator?
For starters, there are three different kinds of magnets that we're going to discuss in this course:
• Electromagnets
• Temporary magnets
• Permanent magnets
To understand what makes them different and why they contain different materials, it helps to know a little bit about what magnets are in general and how they work.
A magnet is an object that can either attract or repel other objects without ever touching them. This works because of a force called a magnetic field. We can't see magnetic fields, but they are a powerful force that's all around us!
Along with learning what a magnet is in school, you might have learned a few other facts:
› Every magnet has a north pole and a south pole.
› Like repels like—if you put the north pole of one magnet next to the north pole of another, they'll push each other away.
› Place certain kinds of metal next to a strong magnet, and the metal will get magnetized, too!
Are you having flashbacks to fourth grade yet? Good! Hold on to those memories—they're going to be helpful coming up.
You also probably learned something about atoms in your science classes. Everything is made of atoms! Atoms have three basic building blocks: Protons, Neutrons, and Electrons.
We'll save the talk about sub-atomic particles like quarks for another day; the electrons are what we're interested in here. Why? Because the movement and positions of electrons are what create a magnetic field around an object.
You might be wondering: if everything has atoms, and atoms have electrons, does that mean everything has a magnetic field? Technically, yes! However, most magnetic fields are too weak to detect. That's why human beings aren't magnets, and we can go around without bumping into everything.
But even atoms themselves have magnetic fields—really, really tiny ones. Again, it's because of the way the electrons are positioned and oriented. Their position means that the magnetic field has an orientation—the force acts in a certain direction.
In certain materials, the atoms' little magnetic fields tend to line up so that they're facing the same way. Together, they combine to create a much stronger field that covers the whole piece of material, which makes that piece a magnet.
The north pole and south pole of a magnet refer to the way all of those little magnetic fields tend to line up. Planet Earth itself is one big, giant magnet, thanks to all of the molten metal churning at its core. That's why a free-floating magnet like the needle of a compass points north. Its magnetic field is lining up with the Earth's!
So now that your head is packed full of ideas, let's put those ideas to use and answer the question you really came here to know.
Think about your grade-school science labs, when you magnetized a bar of iron or steel by placing it next to a really powerful magnet. The iron bar stayed magnetized for a little while, but eventually it faded.
You made a temporary magnet!
In temporary magnets, the atoms' magnetic fields can line up uniformly, but they tend to go back to their normal uncoordinated state after a little while. As a result, temporary magnets retain only a trace amount of magnetism. Temporary magnets are made from what are called ferrous metals, which is a fancy way of saying they're related to iron. They include:
› Iron
› Nickel
› Cobalt
› Steel (which is made from combining iron with other metals)
Temporary magnets are used to make objects like car motors and landline telephones (if you're younger and you don't remember those, ask your parents).
Those powerful magnets in your science labs had to come from somewhere, right? Unlike temporary magnets, the atoms' magnetic fields in permanent magnets tend to stay oriented the same way, or at least take a really long time to fall out of alignment (like teeth ten years after someone stops wearing a retainer).
There's actually a permanent magnet that can be found in nature. It's a particular form of iron ore called magnetite. Explorers of centuries past used to make their compass needles from it. They would use the fact that magnetite compass needles always pointed north as a guide home. That's why they referred to magnetite as lodestone, after the idea of a "leading stone."
These days, it would be way too expensive to mine magnetite just to make refrigerator magnets, so companies make permanent magnets out of combinations of metals called alloys, which they magnetize by placing next to other strong magnets. Some permanent magnet alloy materials include:
› Alnico, a combination of aluminum, nickel, and cobalt
› Ticonal, which is alnico further combined with titanium
› Strontium ferrite
› Samarium cobalt
In each case, the ferrous metal is combined with another material that helps keep its atoms' magnet fields pointing the same way. Aluminum is great for that!
Alnico is flexible and can be used in unusually shaped magnets. Additionally, many permanent magnets are used in radio antennas and other electronics equipment.
One more flashback to your school science lab: did your teacher ever have you do an experiment where you wrapped a wire around an iron bar, connected the ends of the wire to a small battery, and then held a compass up to the iron bar so that the compass needle pointed to it?
If so, then you've made an electromagnet!
An electromagnet uses the electric current flowing inside the wire to line up the small magnetic fields in the bar of iron, turning the bar into a big magnet. Electromagnets are super-temporary magnets—they work as magnets only as long as the electricity is flowing and stop as soon as the power is cut off.
The metal at the core of an electromagnet is usually iron or steel. The wire that wraps around it is made of some kind of flexible metal that can conduct electricity, such as:
› Copper
› Aluminum
Electromagnets are used in a wide variety of equipment. Instruments ranging from a magnetized crane in a junkyard to an MRI machine in a hospital all make use of electromagnets.
Did you realize there would be so much to learn about magnetism when it comes to what's inside your refrigerator magnet? One thing's for certain: learning what makes a magnet a magnet, and how such a practical and useful material works, can be positively electrifying!
