Electrical resistivity and conductivity 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 ("n" = <Z>"n"), but on the scale of the Debye length there can be charge imbalance. In the special case that "double layers" are formed, the charge separation can extend some tens of Debye lengths. The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. A common example is to assume that the electrons satisfy the Boltzmann relation: Differentiating this
Negative number sum of a number and its negation is equal to zero: That is, the negation of a positive number is the additive inverse of the number. Using algebra, we may write this principle as an algebraic identity: This identity holds for any positive number . It can be made to hold for all real numbers by extending the definition of negation to include zero and negative numbers. Specifically: For example, the negation of is . In general, The absolute value of a number is the non-negative number with the same magnitude. For example, the absolute value of and the absolute