For most of recorded history, electricity and magnetism were two unrelated curiosities. The Greeks knew that rubbing amber with fur made it attract small objects, and they knew that certain iron rich stones pulled on iron. Those two facts sat next to each other for roughly two thousand years without anyone suspecting they were the same fact. How they merged is one of the cleanest examples of theory catching up to experiment and then overtaking it.
The Accident That Started It
In 1820 Hans Christian Oersted noticed that a compass needle moved when current flowed through a nearby wire. That is the entire experiment. A current in one place moved a magnet in another place, which meant electricity and magnetism were not separate after all.
Within months Andre-Marie Ampere had the mathematics for the force between current carrying wires. In the 1830s Michael Faraday went the other direction and showed that a changing magnetic field induces a current in a nearby wire. Faraday also gave the field concept its first real shape with what he called lines of force, which is remarkable given that he worked almost entirely without formal mathematics.
Maxwell Unification
In the 1860s James Clerk Maxwell translated Faraday picture into four equations. They describe how charges and currents create electric and magnetic fields, how a changing field of one kind produces the other, and how the pair propagates through space.
Then came the part that still reads as startling. The equations predicted a self sustaining wave travelling at roughly 3 x 10^8 meters per second. That number was already known from optical measurements, because it was the speed of light. Maxwell concluded that light is an electromagnetic wave, and he reached that conclusion from equations written to describe wires and magnets.
Heinrich Hertz confirmed it experimentally in 1887 by generating and detecting radio waves. Radio, television, radar, WiFi and every wireless protocol you have ever debugged descend from that confirmation.
Why It Still Matters To People Who Write Code
Two reasons, and neither one is nostalgia.
The first is that electromagnetism is the physics of the machine you are typing on. Charge moving through a lattice of ions is current, induction is why transformers and wireless charging work, and the whole radio spectrum is one phenomenon sliced by frequency. Knowing the spectrum is continuous makes interference and antenna behaviour far less mysterious.
The second is quantum electrodynamics, the quantum treatment of the same force. It is the most precisely tested theory in science, verified past ten decimal places. When people argue about whether any physics is settled, QED is usually what they are reaching for.
The Shape Of A Good Unification
The pattern is worth borrowing. Two domains looked separate. One experiment linked them. A mathematical description covered both, and that description then predicted something nobody had asked it about, which turned out to be already measured and sitting in another field notebook.
That last step is what separates a good model from a good description. A description reorganizes what you already know. A model tells you something you did not put into it.
The full walkthrough, covering charge and current, electric and magnetic fields, Maxwell equations, the spectrum, induction, and circuits, is here: https://www.learnhowtoscience.com/electromagnetism-explained/
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