Differential Calculus of Vector Fields: Feynman's Physics Explained
To talk about fields that vary from point to point, we need a new calculus and a special operator. The gradient of a field points the way of steepest increase. The divergence measures how much a field spreads out from a point, like a source. The curl measures how much it swirls or circulates around a point. These three ideas are the mathematical vocabulary needed to write the laws of electromagnetism.
The big idea
Gradient, divergence, and curl describe how fields change in space.
Think about it
Think of water flow: what would 'divergence' look like at a drain, and what would 'curl' look like in a whirlpool?
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