How do magnets work?

A pull you cannot see

A magnet is an object that can pull some metals towards itself. The strange thing is that it does not have to touch them. A small magnet can lift a paperclip off a table, even though the whole Earth is pulling that paperclip down. At close range, a small magnet can beat the pull of a whole planet.

Magnets do not attract everything. Only a few metals are strongly attracted to a magnet: iron, nickel and cobalt. Steel is mostly iron, so magnets attract steel too. Aluminium is not attracted, and neither are plastic, wood or glass. Even the type of steel matters. Some stainless steels are magnetic and some are not, depending on the other metals mixed into the steel. A kitchen knife is more likely to stick to a magnet than a kitchen sink.

Magnet safety: small, strong magnets can be very dangerous. If someone swallows two or more, the magnets can pull towards each other inside the body and badly hurt it. Never put a magnet in your mouth or your nose, and keep small magnets away from little children. If anyone swallows one, tell a grown-up straight away so they can get a doctor.

Two poles and an invisible field

Every magnet has two ends, called poles. One is the north pole and the other is the south pole. Opposite poles attract: a north and a south pull together. Matching poles push each other away. Try it with two fridge magnets and you can feel the push. If you cut a magnet in half, you do not get one north piece and one south piece. You get two smaller magnets, and each one has its own north and south pole.

The space around a magnet where you can feel its force is called its magnetic field. You cannot see it, but you can make it show itself. Put a sheet of paper over a bar magnet and sprinkle on iron filings, which are tiny bits of iron. The filings line up along curved lines that run from one pole to the other, as in the photo. The lines bunch together near the poles, which is where the pull is strongest.

The pull gets weaker as you move away from the magnet. But it can pass through things that are not magnetic, such as air and water. That is why a magnet can move a paperclip without touching it.

What is going on inside?

Why are some metals magnetic and others not? The answer is in the atoms. In iron, each atom acts like a tiny magnet with its own north and south. The atoms are grouped into tiny patches called domains, and the atoms in each patch point the same way. In an ordinary piece of iron, though, the patches point every which way. Their pulls cancel out, so the iron is not a magnet.

Now rub an iron nail along a strong magnet, stroking it in one direction again and again. The magnet's field turns the tiny magnets in the nail so that they line up. Their pulls add up instead of cancelling, and the nail becomes a magnet. A magnet can lose its power if the patches get jumbled up again. Very strong heat does this. Iron stops being magnetic at about 770 degrees Celsius.

Magnets that switch on and off

Electricity can make a magnet too. When electricity flows through a coil of wire, the coil makes a magnetic field. When the electricity is switched off, the magnetism disappears. This is called an electromagnet.

A magnet you can switch on and off is very useful. Scrap yards use big electromagnets to lift and move heavy pieces of iron and steel. Hospitals use powerful electromagnets in MRI scanners, which take pictures of the inside of the body. In Melbourne, the Australian Synchrotron uses a series of strong electromagnets to steer electrons round a circular tube hundreds of metres around. As the electrons are bent by the magnetic fields, they give off very bright light, which scientists use to study everything from new materials to food.

The biggest magnet of all: Earth

Earth itself is a giant magnet. Deep down, Earth's core is made mostly of iron and nickel. The outer part of the core is melted, and it moves around as Earth spins. Scientists think this moving metal makes electric currents, and the currents make Earth's magnetic field.

A compass is a tiny magnet that is free to turn. It lines up with Earth's magnetic field, so that one end points towards the north. People have used compasses for hundreds of years to find their way. Earth's magnetic field slowly changes. Geoscience Australia keeps watch on it, including from its magnetic observatory in Canberra. It uses what it learns to keep maps up to date for people who use compasses, from pilots to bushwalkers.

Earth's magnetic field also helps to protect us. It bends away many of the charged particles that stream out from the Sun. Some of them follow the field down towards the poles. Where they crash into gases high in the air, they make glowing lights called auroras. In the south they are called the southern lights, or aurora australis. In Australia they are seen most often in Tasmania and along parts of the Victorian coast.

Some animals seem to sense Earth's magnetic field, including pigeons, bees, salmon and sea turtles. In northern Australia, a termite called Amitermes meridionalis builds mounds that line up roughly north to south, which is why they are often called magnetic termite mounds. When scientists let these termites rebuild the tops of mounds in artificial magnetic fields, the termites seemed to line up the cells inside the mound with the field. That suggests they may use magnetic cues. The direction of the mounds also changes a little from place to place, which suggests it helps the termites cope with local conditions.

📚 Words to know

Magnetic field

The invisible space around a magnet where its pull or push can be felt.

Pole

One of the two ends of a magnet, called north and south, where the pull is strongest.

Domain

A tiny patch of a magnetic metal in which all the atoms point the same way.

Electromagnet

A magnet made by running electricity through a coil of wire. It works only while the electricity is on.

Compass

A tiny magnet that is free to turn, so it lines up with Earth's magnetic field and points north.

🧪 Try this: be a magnet detective

1. Safety first: use only a large, simple magnet, such as a fridge magnet or a toy bar magnet. Never use tiny, strong magnets. Keep every magnet away from mouths and noses, and away from little children.
2. Collect about ten small things from around the house or classroom, such as a paperclip, a key, a coin, a drink can, a food tin, a pencil, a plastic toy, a metal spoon and a piece of foil. Before you test them, write down which ones you think will stick to the magnet.
3. Now test each one. Were any of your guesses wrong? The Royal Australian Mint says that the 5c, 10c, 20c and 50c coins are 75 per cent copper and 25 per cent nickel, and that the $1 and $2 coins are 92 per cent copper, 6 per cent aluminium and 2 per cent nickel. Nickel is a magnetic metal on its own, but mixed with a lot of copper it is not attracted to a magnet, so Australian coins should not stick. Try a fridge magnet on a few coins and see. When metals are mixed together, the mix can behave very differently from the metals on their own, as it does in some stainless steels. A coin from another country might have steel inside, and it could stick.
4. See through paper: put a paperclip on a piece of thin cardboard, then hold the magnet underneath and move it around. The clip follows! Add more layers of cardboard. How many can you add before the clip stops moving? Why do you think that happens?
5. Challenge: ask a grown-up for a large steel nail. Stroke it along one end of the magnet, 30 times, always in the same direction. Does it now pick up a paperclip? Keep the point away from your face.