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 and gave rules regarding operations involving negative numbers and zero, such as ""A debt cut off from nothingness becomes a credit; a credit cut off from nothingness becomes a debt. "" He called positive numbers "fortunes," zero "a cipher," and negative numbers "debts." In the 9th century, Islamic mathematicians were familiar with negative numbers from the works of Indian mathematicians, but the recognition and use of negative numbers during this period remained timid. Al-Khwarizmi in his "Al-jabr wa'l-muqabala" (from which we get the word "algebra") did not use negative numbers or negative coefficients. But within fifty years, Abu Kamil illustrated