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
Positive liberty Berlin described a statement such as "I am slave to no man" as one of negative liberty, that is, freedom from another individual's direct interference. He contrasted this with a Positive Freedom statement such as "I am my own master", which lays claim to a freedom to choose one's own pursuits in life. Charles Taylor sees Negative Freedom as an "opportunity-concept": one possesses Negative Freedom if one is not enslaved by external forces, and has equal access to a society's resources (regardless of how one decides to spend their time). Positive Freedom, says Taylor, is an "exercise-concept": possessing it might