- Electrical conductivity
**Electrical conductivity**or**specific conductivity**is a measure of a material's ability to conduct anelectric current . When anelectrical 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 thecurrent density $mathbf\{J\}$ to theelectric field strength $mathbf\{E\}$::$mathbf\{J\}\; =\; sigma\; mathbf\{E\}$

It is also possible to have materials in which the conductivity is

anisotropic , in which case σ is a 3×3 matrix (or more technically a rank-2tensor ) which is generally symmetric.Conductivity is the reciprocal (inverse) of electrical

resistivity and has the SI units of siemens permetre (S·m^{-1}) i.e. if the electrical conductance between opposite faces of a 1-metre cube of material is 1 Siemens then the material's electrical conductivity is 1 Siemens per metre. Electrical conductivity is commonly represented by the Greek letter σ, but κ 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 resistance.

* An insulator likeglass or avacuum has low conductivity.

* The conductivity of asemiconductor is generally intermediate, but varies widely under different conditions, such as exposure of the material to electric fields or specific frequencies oflight , and, most important, withtemperature and composition of the semiconductor material.The degree of doping in solid state semiconductors makes a large difference in conductivity. More doping leads to higher conductivity. The conductivity of a solution of water is highly dependent on its

concentration of dissolvedsalts and sometimes other chemical species which tend to ionize in the solution. Electrical conductivity of water samples is used as an indicator of how salt-free or impurity-free the sample is; the purer the water, the lower the conductivity or higher.**ome electrical conductivities****Complex conductivity**To analyse the conductivity of materials exposed to alternating electric fields, it is necessary to treat conductivity as a

complex number (or as a matrix of complex numbers, in the case of anisotropic materials mentioned above) called the "admittivity". This method is used in applications such aselectrical impedance tomography , a type of industrial andmedical imaging . Admittivity is the sum of a real component called the conductivity and an imaginary component called the susceptivity. [*http://www.otto-schmitt.org/OttoPagesFinalForm/Sounds/Speeches/MutualImpedivity.htm*]An alternative description of the response to alternating currents uses a real (but frequency-dependent) conductivity, along with a real

permittivity . The larger the conductivity is, the more quickly the alternating-current signal is absorbed by the material (i.e., the more opaque the material is). For details, seeMathematical descriptions of opacity .**Temperature dependence**Electrical conductivity is strongly dependent on

temperature . Inmetal s, electrical conductivity decreases with increasing temperature, whereas insemiconductor s, electrical conductivity increases with increasing temperature. Over a limited temperature range, the electrical conductivity can be approximated as being directly proportional totemperature . In order to compare electrical conductivity measurements at different temperatures, they need to be standardized to a common temperature. This dependence is often expressed as aslope in the conductivity-vs-temperature graph, and can be used::$sigma\_\{T\text{'}\}\; =\; \{sigma\_T\; over\; 1\; +\; alpha\; (T\; -\; T\text{'})\}$

where

:"σ

_{T′}" is the electrical conductivity at a common temperature, "T′":"σ_{T}" is the electrical conductivity at a measured temperature, "T":"α" is the temperature compensation slope of the material,:"T" is the measured absolute temperature, :"T′" is the common temperature.The temperature compensation slope for most naturally occurring

water s is about 2 %/°C, however it can range between (1 to 3) %/°C. This slope is influenced by thegeochemistry , and can be easily determined in alaboratory .At extremely low temperatures (not far from absolute 0 K), a few materials have been found to exhibit very high electrical conductivity in a phenomenon called

superconductivity .**References****ee also***

Classical and quantum conductivity

*Electrical conduction for a discussion of the physical origin of electrical conductivity.

*Electrical resistance

*Electrical resistivity is the inverse of electric conductivity

*Molar conductivity for a discussion of electrolytic conductivity i.e. conductivity due to ions in solution

*SI electromagnetism units

*Transport phenomena

*Thermal conductivity **External links*** [

*http://glassproperties.com/resistivity/ElectrResistMeasurement.htm Measurement of the Electrical Conductivity of Glass Melts*] Measurement Techniques, Definitions, Electrical conductivity Calculation from the Glass Composition

* [*http://environmentalchemistry.com/yogi/periodic/electrical.html Periodic Table of Elements Sorted by Electrical Conductivity*]

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