The Magnetism of Matter: Feynman's Physics Explained

Feynman Vol II10-11

Most materials are only weakly magnetic. Paramagnetism happens when atoms carry permanent magnetic moments that a field tends to line up, slightly strengthening it. Diamagnetism happens in every material, where a field induces tiny atomic currents that oppose it, slightly weakening it. Both effects are usually tiny because thermal motion fights the alignment, and a full explanation needs quantum mechanics.

The big idea

Most matter is barely magnetic — and explaining even that needs quantum theory.

Think about it

If every atom has some magnetism, why isn't every object you touch a magnet?

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