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 parts be expressed in terms of "f" and "f" as Also note that Using these two equations one may express the positive and negative parts as Another representation, using the Iverson bracket is One may define the positive and negative part of any function with values in a linearly ordered group. Given a measurable space ("X",Σ), an extended real-valued function "f" is measurable if and only if its positive and negative parts are. Therefore, if such a function "f" is measurable, so is its absolute value |"f"|, being the sum of two measurable functions. The converse, though, does not necessarily hold: