Revolution has been postponed by a week, so I have to make do with this.
"div" basically calculates for you how much 'stuff' leaves or enters a box (or sphere, or whatever) you draw around something. So imagine, let's say, a lake. You draw a box around the lake. If there's no river taking water away from the lake, then div (water flow) = 0. But if there's a river taking water out of the lake, then div (water flow) = a number, because the water in the river flowing out of the lake crosses the boundary of our imaginary box.
"curl" basically calculates how fast something is rotating. So if I have a plate and I leave it on the table, and I draw a dot on the edge of the plate to measure its rotation, then curl (dot movement) = 0. But if I put that plate in my microwave and it has a turntable, then curl (dot movement) = a number.
What we do in electromagnetism is replace "stuff" with fields. So now what enters or leaves our boxes/spheres/whatever or what we place our dot on isn't something you can pick up and hold.
But the basic idea is the same: We're drawing lines that radiate away or towards positive or negative charges, or which go in and out of north and south poles, and asking "how many lines leave or enter our spheres/boxes/etc?" or "how fast are the lines rotating?"
From that pops out Maxwell's Equations, and thusly, technology. :)
Spoilers follow under the cut.
( Read more... )Nonspoilery: If this helps nonscientific readers get a feel for moving electric and magnetic fields and how what happened in
Revolution, happened, good. :)