The Misconception About Electromagnetic Wave Propagation
If you’ve ever come across explanations of electromagnetic waves in textbooks, videos, or casual discussions, you’ve probably heard something like this:
“A changing electric field creates a changing magnetic field, and a changing magnetic field creates a changing electric field. This back-and-forth is what makes electromagnetic waves propagate.”
It sounds elegant, almost like a perfect dance between electric and magnetic fields. But this explanation, though common, is misleading. It gives the impression that electromagnetic waves are sustained by each field “chasing” the other. In reality, that’s not how nature works. Let’s carefully unpack why.
Where the Idea Comes From
The source of this idea is Maxwell’s equations, the four fundamental laws of electromagnetism. Two of them are particularly relevant here:
- Faraday’s Law of Induction: A changing magnetic field induces an electric field.
- Maxwell–Ampère’s Law: A changing electric field induces a magnetic field.
They in combination with maxwell equations can be written as
It’s tempting to imagine that these two rules imply a self-sustaining feedback loop: the electric field changes, so the magnetic field changes, which makes the electric field change again, and so on. This “infinite chase” is the usual story told in classrooms. But this is an oversimplification—and a wrong one.
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