What is the Debye length?

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What is the Debye length?

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Oversimplifying, it is the length at which a thing’s electric field makes a difference – mostly in plasmas and other situations.

A plasma is a bunch of atoms or molecules that have had some of their electrons stripped, and some free electrons floating around. Each of those things will have some overall electric charge, and so will be creating an electric field around it; pulling or pushing other charged particles towards or away from it.

In theory the electrostatic effect of each particle will extend to infinity. But in practice it will be cancelled out by opposite-charged things nearby. This is why, for example, despite a pencil being made up of loads of charged particles (protons and electrons), the pencil itself doesn’t have any overall charge; the positives and negatives average out over large distances.

So the Debye length tells you how far away from a thing you have to go before its electrostatic effect is meaningless, being cancelled out or drowned out by other particles.