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How does a permanent magnet relate to photons?
Dec 30, 2018

Photons are like ripples in the electromagnetic field 

Think of a large scale magnetic field as the ocean: it happens to have a surface that isn't flat (because the Earth is a sphere, not a plane!). The curvature corresponds to something like the field created by a permanent magnet or a collection of charges. Think of photons as waves propagating about on the surface of the ocean.

The ocean is a very restricted analogy, since it's just characterized by one number (the radius of the Earth) and that number doesn't change from place to place. The actual electromagnetic field is obviously much more complicated. But the point of the analogy is that you can separate the electromagnetic field into a piece that doesn't propagate (like the surface of the ocean) and the ripply bits on top of it that propagate.

A permanent magnet is creating this curvy background bit. If instead you were creating a time-varying magnetic field (by turning the current on and off in an electromagnet) then you would be sending out ripples—photons. By analogy, if you jump up and down in a boat, you can launch waves on the ocean.


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