Cutting a bar magnet in half won’t get rid of its poles. Only two magnets are produced, each with a north pole attracted to the other magnet’s south pole and vice versa.
It’s this basic attraction property that makes magnets useful for so many purposes, from holding a party invitation to a fridge to performing medical imaging.
But how do these poles arise? Why do magnets have north and south poles?
Magnets are “one of the deepest mysteries of physics,” he said Greg Boebinger (opens in new tab), director of the National High Magnetic Field Laboratory in Tallahassee, Florida. While people have been using magnets for thousands of years (opens in new tab)Scientists are still learning new things about the way they work.
The most fundamental answer to why magnets have poles lies in the behavior of electrons. All matter, including magnets, is made up of atoms. In each atomThe nucleus is surrounded by one or more negatively charged electrons. Each of these electrons creates its own tiny magnetic field, which scientists call “spin.” When enough of these small magnetic fields point in the same direction, the material itself becomes magnetic.
Related: Why does metal sparkle in the microwave?
An electron’s “spin” is something of an abstract concept, Boebinger told Live Science. Technically, no one has ever seen a spinning electron — it’s far too small to see under a microscope. But physicists know that electrons have a magnetic field because they have measured it. And one way to create that field would be if the electron spins around. Reverse the direction of the spin and the magnetic field would reverse.
If possible, Electrons pair up so that their spins cancel (opens in new tab), whereby the net magnetism of an atom becomes zero. But with some elements, like iron, that can’t happen. The number of electrons and the way they are positioned around the nucleus means that each iron atom has an unpaired electron that creates a small magnetic field.
In an unmagnetized material, these individual magnetic fields point in different random directions. In this state, they tend to cancel each other out, so the material as a whole is non-magnetic. But under the right conditions, the tiny subatomic magnetic fields can align to point in the same direction. You could think of this as the difference between a crowd of people walking around and everyone getting organized and looking in the same direction. The combination of these very small magnetic fields results in a larger magnetic field – so the material becomes a magnet.
Many of the magnets used in everyday life, such as fridge magnets, are known as permanent magnets. In these materials, the magnetic fields of many atoms in the material have been permanently aligned by an external force – for example, by being placed in a stronger magnetic field.
Often this stronger magnetic field is generated by electricity. Electricity and magnetism are fundamentally related, because magnetic fields are created by the movement of electrical charges. That is why a spinning electron has a magnetic field. But scientists can also use electricity to make very strong magnets, he said Paolo Ferracin (opens in new tab), a senior scientist at Lawrence Berkeley National Laboratory in California. When enough current is passed through a coil of wire, it creates a very strong magnetic field that lasts as long as the current is flowing. These electromagnets are commonly used in physics research, Ferracin told Live Science. They are also used in medical devices such as magnetic resonance imaging (MRI) scanners.
The earth also has its own magnetic field – it’s what makes a compass needle work. Scientists have defined the north pole of a magnet as the end that would point towards the earth’s north pole if the magnet were free to rotate. But technically, Böbinger explained, this means that the north magnetic pole on Earth is actually a south magnetic pole, since opposite poles attract.
In physical convention, the lines of the magnetic field flow outward from the magnet’s north pole and into its south pole, forming a closed loop.
Physicists have also found other arrangements of magnetic poles, including quadrupoles (opens in new tab), in which a combination of magnetic north and south poles are arranged in a square. But one goal remains elusive, Ferracin said: No one has yet found a magnetic monopoly.
Electrons and protons are electrical monopoles: they each have a single electrical charge, either positive or negative. But electrons (and other particles too) have two magnetic poles. And because they are elementary particles, they cannot be further broken down. This difference between the electrical and magnetic behavior of particles has intrigued many physicists, and for some finding a particle with a single magnetic pole is the holy grail. Its discovery would challenge the laws of physics as we currently understand them.
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