Plasma (physics) potential in the space between charged particles, independent of how it can be measured, is called the "plasma potential", or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (formula_6), but on the scale of the Debye length
Positive and negative sets Positive and negative sets In measure theory, given a measurable space ("X",Σ) and a signed measure μ on it, a set "A" ∈ Σ is called a positive set for μ if every Σ-measurable subset of "A" has nonnegative measure; that is, for every "E" ⊆ "A" that satisfies "E" ∈ Σ, one has μ("E") ≥ 0. Similarly, a set "A" ∈ Σ is called a negative set for μ if for every subset "E" of "A" satisfying "E" ∈ Σ, one has μ("E") ≤ 0. Intuitively, a measurable set "A" is positive (resp. negative) for μ if μ is