Electrical conductivity




Electrical conductivity or specific conductivity 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 \mathbf{J} to the electric 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-2 tensor) which is generally symmetric.

Conductivity is the reciprocal (inverse) of metre (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.
  • An insulator like glass or a vacuum has low conductivity.
  • The conductivity of a temperature 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 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.

Some electrical conductivities

Electrical Conductivity

(S·m-1)

Temperature(°C) Notes
Silver 63.01 × 106 20 Highest electrical conductivity of any metal
Copper 59.6 × 106 20
Copper 58.0 × 106 20 Referred to as 100 %IACS or International Annealed Copper Standard. The unit for expressing the conductivity of nonmagnetic materials by testing using the eddy-current method. Generally used for temper and alloy verification of Aluminium.
Aluminium 37.8 × 106 20
Seawater 5 23 Refer to http://www.kayelaby.npl.co.uk/general_physics/2_7/2_7_9.html for more detail as there are many variations and significant variables for seawater.

5(S·m-1) would be for an average salinity of 35 g/kg at about 23(°C) Copyright on the linked material can be found here http://www.kayelaby.npl.co.uk/copyright/

Maybe someone could contact NPL and ask if their information could be reproduced in a separate page here.

Drinking water 0.0005 to 0.05 This value range is typical of high quality drinking water and not an indicator of water quality
Deionized water 5.5 × 10-6 changes to 1.2 × 10-4 in water with no gas present; see J. Phys. Chem. B 2005, 109, 1231-1238

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 as medical imaging. Admittivity is the sum of a real component called the conductivity and an imaginary component called the susceptivity. [1]

Temperature dependence

Electrical conductivity is strongly dependent on temperature. 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 a slope in the conductivity-vs-temperature graph, and can be used:

\sigma_{T'} = {\sigma_T \over 1 + \alpha (T - T')}

where

σT′ is the electrical conductivity at a common temperature, T′
σT 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 waters is about 2 %/°C, however it can range between (1 to 3) %/°C. This slope is influenced by the geochemistry, and can be easily determined in a laboratory.

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.

See 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
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Electrical_conductivity". A list of authors is available in Wikipedia.