Blog post: swansont: 19th Century Physics for $400, Alex

What are Maxwell's Equations?

At first glance it's pretty good, although there are one or two things I think aren't expressed well. One is the divergence of E equation. It's written as being equal to zero, with the explanation that this is true when there are no charges arund. Well, the other form that's discussed,

$latex nablacdot{bf E} = rho/epsilon_{tiny 0}$

is always true. If there are no charges around, rho is zero. I'm not a big fan of equations that are written for specific cases. The first thing that happens is you forget the assumptions and caveats, and then when you try to apply it in general, it fails to work. Use the general equation and then apply the boundary conditions. You'll be better off in the long run.

Then there is this canard:

No! Heat is NOT a part of the EM spectrum. It's true that for room-temperature items and thereabouts, the bulk of the energy radiated is in the infrared part of the spectrum, but not all IR is from thermal sources, so equating the two is wrong. Furthermore, when you get hotter, you start getting visible light. Like from a stove burner or the sun — all of that light we can see? It's still radiant heat!
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