Electrical conductivity

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Electrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity σ is defined as the ratio of the current density J to the magnitude of the electric (vector) field E:

It is also possible to have materials in which the conductivity is anisotropic, different for currents travelling in different directions through the material. In this case σ is a 3×3 matrix (or more technically a rank-2 tensor), which is generally symmetric.

Conductivity is the reciprocal (inverse) of electrical resistivity, ρ, and has the SI units of siemens per metre (S·m-1) and CGSE units of inverse second (s–1):

Electrical conductivity is commonly represented by the Greek letter σ, but κ (esp. in electrical engineering) or γ are also occasionally used.

An EC meter is normally used to measure conductivity in a solution.


Classification of materials by conductivity

  • A conductor such as a metal has high conductivity and a low resistivity.
  • An insulator like glass has low conductivity and a high resistivity.
  • The conductivity of a semiconductor is generally intermediate, but varies widely under different conditions, such as exposure of the material to electric fields or specific frequencies of light, and, most important, with temperature and composition of the semiconductor material.

The degree of doping in semiconductors makes a large difference in conductivity. To a point, more doping leads to higher conductivity. The conductivity of a solution of water is highly dependent on its concentration of dissolved salts, and other chemical species that ionize in the solution. Electrical conductivity of water samples is used as an indicator of how salt-free, ion-free, or impurity-free the sample is; the purer the water, the lower the conductivity (the higher the resistivity). Conductivity measurements in water are often reported as specific conductance, the conductivity of the water at 25 °C.

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