Most of us debug things that ride on electromagnetic waves all day without ever looking at the physics underneath. This is the short version, written for developers, of why radio, WiFi and visible light are literally the same phenomenon.
One Force, Not Two
Until 1820 electricity and magnetism were treated as unrelated curiosities. Then Hans Christian Oersted noticed a compass needle deflect when current ran through a nearby wire. That was the entire experiment, and it meant the two could not be independent.
Andre-Marie Ampere had the mathematics for the force between current carrying wires within months. In the 1830s Michael Faraday showed the reverse, that a changing magnetic field induces a current in a nearby wire.
In the 1860s James Clerk Maxwell turned all of it into four equations. They predicted a self sustaining wave travelling at roughly 3 x 10^8 meters per second, a number already known from optics as the speed of light. Maxwell had derived light from equations written about wires and magnets. Heinrich Hertz generated and detected radio waves in 1887 and confirmed it.
Why The Spectrum Is Continuous
Radio, microwave, infrared, visible light, ultraviolet, X-rays and gamma rays are one phenomenon sliced by frequency. Nothing physical changes at the boundaries between them, only the wavelength and what that wavelength happens to interact with.
Once that clicks, a lot of separate networking facts collapse into one. Antenna length tracking wavelength, why 2.4 GHz passes through a wall better than 5 GHz, why interference shows up where two links share a band. Same equations, different numbers.
Induction Is The Part You Touch Every Day
A changing magnetic field induces a current in any nearby conductor. That is the transformer inside your power brick and the wireless charging pad on your desk.
It is also crosstalk. A fast switching signal trace induces current in the trace beside it whether you wanted that or not, which is Faraday's law showing up as a bug rather than a feature. Ground planes and spacing rules exist because of a discovery from the 1830s.
V = IR. Voltage is the potential difference pushing charge, current is the rate that charge flows, resistance is what opposes it. Measure any two and the third follows.
For hardware faults that is often quicker than reaching for a logic analyzer. A multimeter tells you whether the rail is at voltage, whether current is being drawn, and whether something in the path has gone open or short, and that narrows most problems before you ever look at a waveform.
What Makes This Worth Reading Twice
The pattern is worth borrowing beyond physics. Two domains looked separate, one experiment linked them, and a single mathematical description then covered both. That description went on to predict something nobody had put into it, and the prediction turned out to be a number already measured in a different field.
A description reorganizes what you already know. A model tells you something you did not.
The full walkthrough, covering charge and current, electric and magnetic fields, the four equations, the spectrum, induction and circuits, is in this guide to how electromagnetism works.