Electrical Conductivity

Information about Electrical Conductivity

Not to be confused with electrical conductance, a measure of an object's or circuit's ability to conduct an electric current between two points, which is dependent on the electrical conductivity and the geometric dimensions of the conducting object.

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 $\text{[math]}$ to the electric field strength $\text{[math]}$ :

$\text{[math]}$ .

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 electrical resistivity and has the SI units of siemens per 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 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 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 dissolved salts 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.

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
Annealed 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 [1] 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 [2] 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 air saturated water; 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 electrical impedance tomography, a type of industrial and medical imaging. Admittivity is the sum of a real component called the conductivity and an imaginary component called the susceptivity. [3]

Temperature dependence

Electrical conductivity is strongly dependent on temperature. In metals, electrical conductivity decreases with increasing temperature, whereas in semiconductors, electrical conductivity increases with increasing temperature. Over a limited temperature range, the electrical conductivity can be approximated as being directly proportional to 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:

$\text{[math]}$

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 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.

External links

Measurement of the Electrical Conductivity of Glass Melts Measurement Techniques, Definitions, Electrical conductivity Calculation from the Glass Composition
Periodic Table of Elements Sorted by Electrical Conductivity

Electrical conductance is the reciprocal of electrical resistance. It is a measure of how easily electricity flows along a certain path through an electrical element. The SI derived unit of conductance is the siemens (formerly referred to as the reciprocal ohm or mho).
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Conduction is the movement of electrically charged particles through a transmission medium (electrical conductor). The movement can form an electric current in response to an electric field. The underlying mechanism for this movement depends on the material.
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Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second.

Definition

The amount of electric current (measured in amperes) through some surface, e.g.
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Electric potential is the potential energy per unit of charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. It is a scalar quantity.
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Current density is a measure of the density of electrical current. It is defined as a vector whose magnitude is the electric current per cross-sectional area. In SI unit, the current density is measured in amperes per square meter.
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electric field. This electric field exerts a force on other electrically charged objects. The concept of electric field was introduced by Michael Faraday.

The electric field is a vector field with SI units of newtons per coulomb (N C⁻¹
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Anisotropy (pronounced with stress on the third syllable, IPA: /ˌænaɪˈsɒtrəpi/) is the property of being directionally dependent, as opposed to isotropy, which means homogeneity in all directions.
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matrix (plural matrices) is a rectangular table of elements (or entries), which may be numbers or, more generally, any abstract quantities that can be added and multiplied.
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The term tensor has slightly different meanings in mathematics and physics. In the mathematical fields of multilinear algebra and differential geometry, a tensor is a multilinear function.
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In linear algebra, a symmetric matrix is a square matrix, A, that is equal to its transpose

The entries of a symmetric matrix are symmetric with respect to the main diagonal (top left to bottom right).
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multiplicative inverse for a number x, denoted by ¹⁄_x or x⁻¹, is a number which when multiplied by x yields the multiplicative identity, 1.
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invertible or non-singular if there exists an n-by-n matrix such that

where denotes the n-by-n identity matrix and the multiplication used is ordinary matrix multiplication.
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Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrical charge.
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The siemens (symbol: S) is the SI derived unit of electric conductance. It is named after the German inventor and industrialist Ernst Werner von Siemens, and is equivalent to the previously used designation of this unit, the mho.
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in

The metre or meter^[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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Greek alphabet
Child systems Gothic
Glagolitic
Cyrillic
Coptic
Old Italic alphabet
Latin alphabet

ISO 15924 Grek

Note: This page may contain IPA phonetic symbols in Unicode.
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Sigma (upper case Σ, lower case σ, lower case in word-final position ς) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 200.
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Kappa (uppercase Κ, lowercase κ or ϰ) is the 10th letter of the Greek alphabet, used to represent the voiceless velar stop, or "k", sound in Ancient and Modern Greek.
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Gamma (uppercase Γ, lowercase γ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. It was derived from the Phoenician letter Gimel .
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In science and engineering, conductors, such as copper or aluminum, are materials with atoms have loosely held valence electrons. See electrical conduction.

Conductors in context

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The Macro Expansion Template Attribute Language complements TAL, providing macros which allow the reuse of code across template files. Both were created for Zope but are used in other Python projects as well.
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Glass is a noncrystalline material that can maintain indefinitely, if left undisturbed, its overall form and amorphous microstructure at a temperature below its glass transition temperature.
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A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than standard atmospheric pressure. The Latin term in vacuo is used to describe an object as being in what would otherwise be a vacuum.
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A semiconductor is a solid that has electrical conductivity in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically.^[1] Semiconductors are tremendously important in technology.
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Light is electromagnetic radiation of a wavelength that is visible to the eye (visible light). In a scientific context, the word "light" is sometimes used to refer to the entire electromagnetic spectrum.
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trillion fold).]]

Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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This article is about chemical solutions. For other uses, see Solution (disambiguation).

In chemistry, a solution is a homogeneous mixture composed of two or more substances.
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Water (H₂O, HOH) is the most abundant molecule on Earth's surface, composing of about 70% of the Earth's surface as liquid and solid state in addition to being found in the atmosphere as a vapor.
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In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of
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