Conductances

Conductances are measures of how easily electric current can flow through a component or medium. They are the reciprocal of resistance, G = 1/R, and their unit is the siemens (S). The relationship between current and voltage can be written as I = G V, with I as current and V as voltage.

In circuits, conductances add in parallel: the total conductance is the sum of the individual conductances. In series, resistances add, so the overall conductance is not simply additive. For nonlinear devices, conductance can depend on voltage or current, complicating the simple linear picture.

Conductance is used across domains. Electrical conductance applies to metals, semiconductors, and electrolytes. In biology, membrane conductance (Gm) describes how readily ions cross a cell membrane; it is often characterized by the derivative dI/dV and can change with the opening and closing of ion channels. Other related concepts include thermal conductance, the analogous quantity for heat flow, and chemical conductance in electrochemical systems.

Practical considerations include the dependence of conductance on geometry and temperature. Generally, G is proportional to cross-sectional area and inversely proportional to length in a given material, with material properties and environmental conditions (such as temperature) also playing key roles. Understanding conductance requires attention to the context, since the same term can describe different but related transport phenomena.