Electromagnetism is everywhere, and humans have observed its many guises for thousands of years. Ancient Egyptians were painfully aware of the Nile River’s electric catfish. The Chinese learned to navigate with magnetized lodestone compasses in the first millennium B.C.E. Our early ancestors must have craned their necks in awe when a lightning bolt lit up the night sky.
Despite this long acquaintance with all sorts of electrical and magnetic phenomena, no one suspected until the early 1800s that the two were inextricably linked (let alone that these twin forces create waves of energy). Over the next century, however, a handful of brilliant thinkers and experimenters gradually unraveled the mysteries of electromagnetism.
What Is Electromagnetism?
Electromagnetism involves the interaction between electrically charged particles. It combines electricity and magnetism into a single theory and is responsible for various phenomena, such as the generation of electric currents and magnetic fields.
We use electromagnetism every day with electric motors, radio and television broadcasting, and medical equipment like MRI machines. To put it simply, it's how electric charges produce magnetic fields and how changing magnetic fields create electricity. Here are the groundbreaking contributions physicists made to the field of electromagnetism.
1. Hans Christian Ørsted
During a lecture in 1820, Ørsted, a Danish physicist, stumbled upon the first clue: He found that when he ran electricity through a wire, the needle of a compass held nearby would deflect from its normal alignment with magnetic north until it lay perpendicular to the current. In other words, he discovered that electric currents create magnetic fields.
Accounts differ as to whether Ørsted was looking for this result or accidentally discovered it. Regardless, it was the first sign of an intimate relationship between electricity and magnetism and a major inspiration for the next key player in the story.
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2. Michael Faraday
Following Ørsted’s demonstration, his contemporaries began to wonder if the effect would work in reverse — that is, if a magnet could create an electric current. With this in mind, Faraday, an English physicist, tried his own experiment.
In August 1831, he wound two coils of insulated wire around opposite sides of an iron ring. One was connected to a battery, thereby magnetizing the iron, and the other was connected to a galvanometer to detect electric current. Faraday wanted to see whether the magnetic field produced by the first wire would electrify the second.
At first, the results were puzzling. To his amazement, the galvanometer briefly registered a current in the second wire whenever he turned on the current in the first and again when he turned it off, but nothing in between. He realized it was not the mere presence of a magnetic field causing the current, but a change in the magnetic field. He later got the same outcome by moving a magnet in and out of a coil of wire.
Faraday had discovered a process known as electromagnetic induction and simultaneously invented the first electrical transformer. In fact, his work laid the foundation for much of the modern technology we hold most dear, including the infrastructure that generates and distributes power to our homes.
3. James Clerk Maxwell
Due to his poor upbringing and lack of formal education, Faraday was always a far better experimenter than mathematician. But the same year he made his greatest discovery, the man who would give it a rigorous theoretical framework was born.
In 1865, Maxwell, a Scottish physicist, published a set of four elegant equations that described the relationship between electricity and magnetism, finally unifying a range of phenomena that generations of scientists had struggled to understand. What’s more, they predicted the existence of electromagnetic waves.
Maxwell correctly guessed that these waves were the stuff of visible light, and later researchers proved the same for the rest of the electromagnetic spectrum: gamma-rays, x-rays, ultraviolet, infrared, microwaves, and radio waves.
Albert Einstein (who did a great deal to advance Maxwell’s theory himself) ranked him an equal of Sir Isaac Newton, the scientific community’s long-standing paragon. As he put it: “One scientific epoch ended, and another began with James Clerk Maxwell.”
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4. Heinrich Hertz
Maxwell gave the world theoretical reason to believe in electromagnetic waves, but it was Hertz, a German physicist, who confirmed their existence experimentally.
Hertz was captivated by Maxwell’s equations. He saw that they implied a whole spectrum of electromagnetic frequencies, both shorter and longer than the small portion human eyes can see, and he set out to capture these spectral waves.
He used an induction coil (not unlike Faraday’s) to create electromagnetic waves and a spark gap between two brass spheres to detect them. The spark was dim, lasting only a fraction of a second, but in a dark room with well-adjusted eyes, Hertz was able to glimpse it — proof of radio waves, the shortest electromagnetic frequency. In later experiments, he also showed that their speed was equal to that of visible light.
His discoveries enabled the development of radio broadcasts, television, satellite communication, and even the WiFi that pervades 21st-century life.
5. Albert Einstein
Hertz’s experiments seemed to settle an age-old debate: Was light made of waves or particles? But as we know now, he’d only revealed half the picture — it’s both simultaneously.
The world had incontrovertible proof of light’s waviness. Then, in 1905, the same year Einstein published his special theory of relativity, he showed in a separate paper that electromagnetism must also be considered as a bunch of discrete particles.
The paper (which later won him a Nobel prize) was an explanation of the photoelectric effect, in which light shining on a metal surface causes that surface to emit electrons. Physicists had been unable to explain this phenomenon with classical wave theory, so Einstein introduced a new concept: the quantization of light.
He realized that although light could behave as a wave, it had to consist of minuscule packets of energy or light quanta. Today, these are known as photons, and they are the other half of “wave-particle duality.” More than a century later, scientists still recognize this as light’s true (albeit bewildering) nature.
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