What Is a Magnet?

A magnet is an object that produces an invisible magnetic field: an area of space where magnetic forces act. Every magnet has two ends, called the north pole and the south pole. Opposite poles attract; like poles repel. Magnets can pull on certain metals (especially iron, nickel and cobalt), and on other magnets. Earth itself is a giant magnet, with its own north and south magnetic poles. Magnets are used in fridges, motors, speakers, computers, MRI scanners and many other technologies.

• What it doesProduces a magnetic fieldAttracts iron, nickel, cobalt
• Two polesNorth and southSame poles repel, opposite attract
• Cannot have only one poleAlways pairsCut a magnet, get two smaller magnets
• Magnetic metalsIron, nickel, cobaltPlus some alloys
• Strongest natural magnetsNeodymiumMade with rare-earth metals
• Earth is a magnetField protects us from space radiationHelps compasses point north

Why some materials are magnetic

Inside any metal, each atom acts like a tiny magnet because of the spinning electrons within. In most materials, these tiny atomic magnets point in random directions and cancel each other out. In a few special materials (iron, nickel, cobalt), the tiny magnets can line up in the same direction, making the whole object magnetic.

This lining-up happens in tiny regions called domains. In an ordinary iron nail, the domains point in random directions and cancel. Bring it near a strong magnet, though, and the domains line up: the nail becomes magnetic too. That is why a magnet can pick up iron nails one after another in a chain.

The two poles

Every magnet has a north (N) pole and a south (S) pole. They behave like:

• N and S: attract (opposite poles).
• N and N: repel (like poles).
• S and S: repel.

The poles are named after Earths magnetic poles. A magnetic compass needles "north pole" actually points to Earths magnetic North, because Earths North Pole is technically a magnetic SOUTH (and opposite poles attract). Confusing but true.

Magnetic fields

The invisible region of force around a magnet is its magnetic field. The field flows out of the north pole, curves around, and re-enters at the south pole, forming closed loops. You can see the field shape using iron filings:

• Sprinkle iron filings on a piece of paper.
• Place a bar magnet under the paper.
• Tap the paper gently. The filings line up along the magnetic field lines, making the field shape visible.

Fact No matter how many times you cut a magnet in half, each piece is still a magnet with a north and a south pole. You can never get just a north pole or just a south pole by itself. Physicists call this "no magnetic monopoles". Some theoretical physics ideas predict that single poles ought to be possible, but despite decades of careful searches, none has ever been found.

Earths magnetic field

Earth itself acts like a giant bar magnet, with magnetic poles near (but not exactly at) the geographic North and South Poles. The field is thought to come from the slow swirling of molten iron in Earths outer core, deep underground.

Earths magnetic field does many useful things:

• It deflects the deadly stream of charged particles from the Sun (the solar wind), protecting our atmosphere and life on the surface.
• It steers solar particles toward the poles, where they trigger the colourful displays of the aurora.
• It makes compasses work, allowing navigation by anyone with a small magnetic needle.
• It is sensed by some animals (birds, fish, even bacteria) that use it to migrate over thousands of kilometres.

Different kinds of magnet

• Permanent magnets: stay magnetic on their own. Bar magnets, horseshoe magnets, fridge magnets and neodymium "rare-earth" magnets.
• Temporary magnets: become magnetic when near another magnet but lose magnetism when the magnet is removed. Iron nails are temporary magnets.
• Electromagnets: coils of wire that become magnets only when an electric current flows through them. Powerful, switchable, and the basis of motors and generators. (See electromagnets.)

Where magnets are used

• Fridge magnets: small flexible magnets used for decoration and to hold notes.
• Electric motors: use magnets to convert electrical energy into rotation.
• Loudspeakers and headphones: use magnets to push a paper or plastic cone back and forth, making sound.
• Computer hard drives: store information as patterns of magnetic spots on spinning discs.
• Credit cards and tickets: contain magnetic strips with encoded information.
• Compass: a small magnet free to swing, points to Earths magnetic North.
• MRI scanners: use powerful superconducting magnets to image inside the human body.
• Maglev trains: float above the track on powerful magnets.
• Particle accelerators: like the CERN Large Hadron Collider, use magnets to steer particles around the ring.

Did you know? Earths magnetic poles do not stay in one place. They wander slowly over the years. The North Magnetic Pole is currently moving from Canada towards Siberia at about 55 km per year: faster than at any point in recorded history. Every few hundred thousand years, Earths poles even flip completely: the magnetic North becomes the magnetic South and vice versa. The last full reversal was about 780,000 years ago.

Magnetic versus non-magnetic metals

People often think all metals are magnetic. They are not. Only a few specific metals strongly attract to magnets:

• Iron and most steel: very magnetic.
• Nickel: magnetic.
• Cobalt: magnetic.
• Stainless steel: usually NOT magnetic (it is mostly iron, but with chromium and nickel added in proportions that disrupt magnetism).
• Aluminium, copper, gold, silver, lead, brass, zinc, tin: not magnetic.

That is why you can test whether a "silver" coin is real silver by holding a magnet near it: silver should not be attracted. Real gold also fails to attract. If a "gold" or "silver" item is pulled by a magnet, it is probably mostly iron or steel with a thin coating.

Try this Take a magnet around your home and test what is magnetic. Try fridge doors (yes, the steel inner panel), forks and spoons (depends on the metal), aluminium foil (no), pound coins (sometimes), the screws on door hinges (yes), the body of a torch (depends). Make a list of magnetic vs non-magnetic objects. Be careful not to bring strong magnets near electronics, credit cards or hard drives: they can erase or damage them.

Deeper dive: how Earths magnetic field protects life

The Sun constantly blows out a stream of charged particles called the solar wind: protons, electrons and alpha particles, all moving at hundreds of kilometres per second. The solar wind carries enough energy to slowly strip away a planets atmosphere over billions of years. Worse, during a solar storm, the Sun can emit huge bursts of radiation that would damage living cells and electronics.

Earth has a defence: its magnetic field. The field stretches out tens of thousands of kilometres into space, deflecting most of the solar wind around our planet. The protected bubble of space inside the field is called the magnetosphere.

Mars has almost no magnetic field. Billions of years ago, Mars probably had a thicker atmosphere, perhaps even oceans of liquid water. With no magnetic shield, the solar wind slowly stripped its atmosphere away, leaving the cold, dry world we see today.

Some of the solar wind does sneak into Earths magnetic field near the poles. These particles spiral down along the field lines and hit the upper atmosphere, exciting nitrogen and oxygen atoms which then glow. The result is the spectacular aurora: green and red lights in the northern sky (the aurora borealis) and southern sky (aurora australis).

Major solar storms can damage satellites, radio communications and even power grids on Earth. The 1989 storm knocked out power across Quebec, Canada, for 9 hours. A repeat of the so-called Carrington Event of 1859 (the biggest known solar storm) could cripple modern electrical infrastructure for months. Engineers now monitor space weather constantly and can shut down vulnerable systems if a big storm is coming.

Without our magnetic shield, life as we know it might never have been possible on Earth. The same invisible force that lets a fridge magnet stick to your fridge also lets you exist at all.

For more, see electromagnets and Earths magnetic field.