Magnets, How Do They Work? On the Magic of Magnetic Force
Roma Agrawal Explains the Technology Behind Telegraphs, Touchscreens, and More
A message had arrived at the telegram office that morning. As the mailman approached the seaside apartment in Mumbai, India, that my grandfather Brij Kishore shared with my grandmother Chandrakanta and their four children, he felt his throat tighten as she pulled on his sleeve and said, “Taar aaya hai.” In Bombay in the 1960s, the arrival of a “taar”—a telegram—usually meant bad news. Few homes had telephones, so far-flung family would send updates of their children, cooking, and cricket scores via the well-named snail mail. Only if a matter was more pressing and urgent would they send the news via telegram.
Babuji, as we all called him, tore open the envelope and took out a sheet of pale blue paper. On it was glued a strip of white paper that contained three words: ANXIOUS TO RETURN. He looked at his wife, rolled his eyes, and reassured her that there was nothing to worry about.
After graduating college, Babuji’s son Shekhar had traveled to Italy to look for work. Evidently, he didn’t like it there and wanted to return, but Babuji was determined that Shekhar should give it a shot. So, he put on his chappals and walked down to the post office to send a telegram saying so, using as few words as possible, because telegrams weren’t cheap and were charged by length. Over the next few weeks, many more telegrams arrived from Italy, begging for a ticket back to Bombay. After ignoring many of them, Babuji finally relented. His son, my uncle, returned to Bombay, where he lived out his days.Magnets—or objects that exert magnetic forces—exist in the very essence of our universe.
Less than sixty years later, each week of pandemic lockdown was punctuated by the demanding squeaks of my toddler: “I want talk Nani right now!” The child of a pandemic, there were eighteen months of her life when she couldn’t see her grandparents in person, so her demands to speak to her grandma were swiftly obeyed. With the swish of a finger on a touchscreen, a call flew through the air to the other side of the planet, to which my mom responded. She saw my daughter crawl for the first time, and speak her early words, in color, live, on the screen of a smartphone. When I stop to think about the ease with which we were able to stay in touch through those tough times, I find myself not only in awe of how far we have come but also immensely grateful.
We have been through a radical shift in technology across just three generations of my family, and each step of the way has changed our lives dramatically, just as they did for society as a whole: allowing us to communicate with our loved ones, creating the world of instant news, changing the way we work, and altering the way we entertain and are entertained. But while a video call may seem a far cry from the telegram, all these forms of modern communication are based on the science of signals being sent from one distant point to another, almost instantaneously. And our ability to do that centers around magnets.
I find magnets magical. The magnetic fields that radiate from them are invisible, but they can be substantial, far-reaching, and influential across large distances. The science is complex and wasn’t understood for thousands of years—indeed, many physicists will tell you that magnetism, and especially electromagnetism, still isn’t fully understood. But once we had at least some understanding, we were able to create practical mechanisms. Humans harnessed the magic of magnets to create machines that could interact and exert forces on other machines, farther away than had ever been thought possible.
Unlike the inventions we’ve looked at so far, magnets—or objects that exert magnetic forces—exist in the very essence of our universe. You and I are magnets (very, very weak ones—don’t worry, there’s no danger of us suddenly becoming attached to our refrigerators). Atoms, the minuscule building blocks of matter, are magnetic. The planet on which we live is a giant magnet. Magnets, unlike wheels and nails and springs, were discovered rather than invented by humans. Despite this, they nonetheless deserve their place in this book, because it was humans who figured out how to make them more useful than they were as supplied by Mother Nature. The magnets we found naturally in our surroundings a few thousand years ago were weak and hard to come by. They were formed of magnetite, which came to be known as lodestone, a natural mineral found in the earth that is a mix of iron and oxygen, plus other impurities. It’s a magnetic material, but only a small proportion of the magnetite that exists in nature is magnetic, because it needs both a specific combination of impurities inside it, and to have been exposed to specific conditions of heat and magnetic fields outside it.
The earliest references to this natural magnet date back to ancient Greece in the sixth century BCE. Around two hundred years later, the Chinese documented the phenomenon of a natural stone attracting iron, and in another four hundred years, they began using this material for geomancy (a form of divination). It took another thousand years, advancing into the Middle Ages, before it was used for navigation in the form of a compass. Navigators in the Song Dynasty in China shaped lodestone to look like a fish, and let it float freely in water, so it pointed south. This knowledge spread to Europe and the Middle East soon after. Even then, with over a thousand years of knowing about natural magnets, we couldn’t replicate them, and their use was restricted to navigation.
Magnets themselves come in two distinct forms: permanent magnets and electromagnets. Permanent magnets are the horseshoe- and bar-shaped magnets we saw in school science demonstrations and those that decorate our refrigerators. They have two poles, north and south: bringing together the south poles or the north poles of two magnets creates a pushing or repulsion force, but bring a north and south pole together and the magnets will cling to each other.
It took millennia to come to grips with how magnetism works, because this requires an advanced understanding of atomic physics and material science. To become a magnet, a material requires many particles, at many different scales, behaving in a very particular way. Let’s start with the electrons that orbit the nucleus of an atom. Just as electrons have a negative electric charge, they also have what physicists call spin, which defines its magnetic characteristics. By “pointing” in different directions, the spin cancels out the magnetic forces of electrons entirely in some atoms, leaving them nonmagnetic. But in others, while some of the electrons are arranged so their spin cancels out, not all are, so there is a net magnetic force left over, creating a magnetic atom.
Then, if we zoom out from the electron scale to the atomic scale, the atoms in an element are naturally arranged at random, which means that the magnetic forces of the individual atoms cancel each other out. In some materials, however, little pockets of atoms—called domains—have atoms all arranged in the same direction, giving the domain a net magnetism. However, they are not yet magnets, because the domains themselves are usually arranged at random.
To make a material produce a net magnetism, then, the atoms in the majority of the domains need to be forced into magnetic alignment by a strong external magnetic field, or by large amounts of heat applied at particular temperatures in particular sequences. Once the domains point in the same direction, you have a magnet.
Even today, there is a debate as to how magnetite becomes magnetized in the first place, so artificially replicating this has been a challenge. Certain materials like iron, cobalt, and nickel have electrons favorably arranged to make their atoms magnetic, which in turn sit in well-defined domains. Our ancestors tinkered with mixes of such metals, heating and cooling them in various combinations to try to figure out the best recipe for forming permanent magnets. They succeeded, to a degree, making somewhat weak magnets that didn’t hold their force for long.
The development of permanent magnets in a scientific way started in the seventeenth century, when Dr. William Gilbert published De Magnete, which outlined his experimentation with magnetic materials. In the eighteenth and nineteenth centuries, we developed more sophisticated methods for making iron and steel, and observed that certain combinations made much stronger or longer-lasting magnets—and sometimes even both. But we still didn’t really understand why. The nineteenth century also saw the advent of understanding electromagnetism, which we’ll come back to, but it took until the twentieth century and the conception of quantum physics before we were able to define and understand atoms and electrons well enough to create strong and long-lasting permanent magnets ourselves.
This led to the use of three types of materials to make permanent magnets: metals, ceramics, and rare-earth minerals. The first major improvement was the development of a metal mix of aluminum-nickel-cobalt, used to make “alnico” magnets, but these were complicated and expensive to make. Then in the 1940s, ceramic magnets were created from pressing together tiny balls of barium or strontium with iron. These were much cheaper, and today account for the vast majority of permanent magnets produced by weight. The third family of materials are the rare-earth magnets, based on elements like samarium, cerium, yttrium, praseodymium, and others.
Within the space of the last century, these three types of permanent magnets have been refined to produce produced magnetic fields 200 times stronger than before. And this improved efficiency led to permanent magnets playing an important role in much of our modern lives: a car, for example, can have thirty separate applications for magnets, using over 100 individual magnets. Thermostats, door latches, speakers, motors, brakes, generators, body scanners, electric circuitry and components—take any of these apart and you’ll find permanent magnets.
But as we saw, the stories of permanent magnets and electromagnets intertwine, and since the discovery of electromagnets around 200 years ago, each has swung in and out of favor as humanity learned more about how they worked and what they could be used for. The prevalence of permanent magnets in the past few decades is due not just to their increasing strength and compactness but also to the fact that, unlike electromagnets, they never need a source of power. But from the nineteenth century onward, and even today in situations where immense fields are needed, electromagnets dominated. We can control their strength, switching off or cranking up the magnetic field of an electromagnet when it suits.
The reason electromagnets took so long to make an appearance in the field is because we needed an understanding of the science of materials, electricity, and light—and the mysterious force of electromagnetism. It’s only when we were able to move electrons in materials that we understood how to create and change this force and apply it to our technology.
Like gravity, electromagnetism is one of the fundamental forces in nature. It is the physical interaction that happens between particles, like electrons, that have an electric charge. In the late eighteenth and early nineteenth centuries, André-Marie Ampère, Michael Faraday, and other scientists published numerous theories about electric and magnetic fields, which were eventually brought together and summarized by the mathematician James Clerk Maxwell in what are now known as “Maxwell’s equations.” These gave us crucial information that led to the invention of electric motors, and these equations are also the basis of our power grids, radios, telephones, printers, air conditioners, hard drives, and data-storage devices; they are even used in the creation of powerful microscopes.
The key principle that led to such technological advancement was the realization that moving charges create magnetic fields. Without getting too deep into the complex science, this means that if an electric current is flowing through a coil of wire, it behaves like a magnet. If you change the strength of the current, you change the strength of the magnet. And the converse is also true: applying a variable magnetic field near a wire will create an electric current in the wire. Following on from this science, experiments proved that when a charge, like an electron, moves within a magnetic field (either freely or inside a wire), it feels a pushing force.
Studying the electromagnetic force led us to define the phenomenon of electromagnetic waves. Think of these as waves of force that flow because of the interaction between electric and magnetic fields. Our understanding of light increased manifold when we were able to quantify it as an electromagnetic wave. And, in addition to visible light, we saw that a whole spectrum of electromagnetic waves—from radio waves (with the longest wavelength) to gamma rays (with the shortest)—exists, and that these waves can be used in different ways. It is electromagnetism and electromagnetic waves that form the basis of our long-range communication technology: the technology used by countless people around the world to share news with their loved ones. People like my uncle, the prolific sender of telegrams.
From Nuts and Bolts: Seven Small Inventions That Changed the World in a Big Way by Roma Agrawal. Copyright © 2023. Available from W.W. Norton & Company.