Conductance

Conductance is a measure of how readily electric current can flow through a material or device in response to an applied voltage. It is the reciprocal of resistance, expressed as G = 1/R, and is denoted by the symbol G. The SI unit of conductance is the siemens (S), which is equal to amperes per volt (A/V). The unit mho, or ohm inverse, is an alternative historical name for the same unit.

In a simple, uniform conductor of length L and cross-sectional area A, with electrical conductivity σ (the reciprocal of resistivity ρ), conductance is given by G = σ A / L = A / (ρ L). This shows how geometry and material properties jointly determine conductance. For complex or nonuniform geometries, the overall conductance depends on the spatial distribution of conductivity and can be analyzed by solving the appropriate electromagnetic field equations or by decomposing the circuit into elements and using network rules.

In circuit analysis, conductance is used to describe how easily current can transfer between two nodes. In parallel configurations, conductances add (G_total = G1 + G2 + …), while in series configurations the reciprocal conductances add (1/G_total = 1/G1 + 1/G2 + …). Conductance is also encountered in related contexts, such as thermal conductance (the rate of heat transfer per unit temperature difference, measured in W/K) and ionic conductance in electrolytes or biological ion channels, where it reflects the mobility and concentration of charge carriers.

Overall, conductance provides a convenient measure of the ease of electrical or analogous transport, bridging material properties and geometric factors.