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 "a" as follows: The justification for why the product of two negative numbers is a positive number can be observed in the analysis of complex numbers. The sign rules for division are the same as for multiplication. For example, and If dividend and divisor have the same sign, the result is always positive. Another method of dividing negative numbers is that if one of the numbers being divided is a negative, the answer will be negative. The negative version of a positive number is referred to as its negation. For example, is the negation of the positive number . The