Electrical conductivity

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Electrical conductivity

Electrical conductivity or specific conductance is a measure of a material's ability to conduct

Electrical conduction

Electrical conduction is the movement of electric charge particles through a transmission medium . The movement of charge constitutes an Current ....
an electric current

Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity s is defined as the ratio of the current density

Current density

Current density is a measure of the density of flow of a conserved charge . Usually the charge is the electric charge, in which case the associated current density is the electric current per unit area of cross section, but the term current density can also be applied to other conserved quantities....
to the electric field

Electric field

In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field ....
strength :

It is also possible to have materials in which the conductivity is anisotropic, in which case s is a 3×3 matrix

Matrix (mathematics)

In mathematics, a matrix is a rectangular array of numbers, as shown at the right. In addition to a number of elementary, entrywise operations such as matrix addition a key notion is matrix multiplication....
(or more technically a rank-2 tensor

Tensor

A tensor is an object which extends the notion of Scalar , Vector , and Matrix . The term has slightly different meanings in mathematics and physics....
) which is generally symmetric

Symmetric matrix

In linear algebra, a symmetric matrix is a square matrix, A, that is equal to its transposeThe entries of a symmetric matrix are symmetric with respect to the main diagonal ....
.

Conductivity is the reciprocal (inverse

Invertible matrix

In linear algebra, an n-by-n matrix A is called invertible or non-singular if there exists an n-by-n matrix B such that...
) of electrical resistivity

Resistivity

Electrical resistivity 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....
, , and has the SI units of siemens

Siemens (unit)

The siemens is the SI SI derived unit of electric conductance. It is equal to inverse ohm. It is named after the Germany inventor and industrialist Ernst Werner von Siemens, and was previously called the #Mho....
per metre

Metre

The metre or meter is a Unit of measurement of length. It is the SI base unit of length in the metric system and in the International System of Units , used around the world for general and scientific purposes....
(S·m^-1):

.

Electrical conductivity is commonly represented by the Greek letter

Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
s, but ?

Kappa

File:Greek lowercase kappa variant.svgKappa is the 10th letter of the Greek alphabet, used to represent the voiceless velar stop, or "k", sound in Ancient Greek and Modern Greek....
or ?

Gamma

Gamma 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 alphabet Gimel ....
are also occasionally used.

An EC meter

EC meter

An electrical conductivity meter measures the electrical conductivity in a solution. Commonly used in hydroponics, aquaculture and freshwater systems to monitor the amount of nutrients, salts or impurities in the water....
is normally used to measure conductivity in a solution.

Classification of materials by conductivity

The degree of doping in solid state semiconductors makes a large difference in conductivity.

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Encyclopedia

Electrical conductivity or specific conductance is a measure of a material's ability to conduct

Electrical conduction

Electrical conduction is the movement of electric charge particles through a transmission medium . The movement of charge constitutes an Current ....
an electric current

Electric current

Current density

Electric field

Matrix (mathematics)

Tensor

A tensor is an object which extends the notion of Scalar , Vector , and Matrix . The term has slightly different meanings in mathematics and physics....
) which is generally symmetric

Symmetric matrix

Invertible matrix

In linear algebra, an n-by-n matrix A is called invertible or non-singular if there exists an n-by-n matrix B such that...
) of electrical resistivity

Resistivity

Siemens (unit)

Metre

Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
s, but ?

Kappa

File:Greek lowercase kappa variant.svgKappa is the 10th letter of the Greek alphabet, used to represent the voiceless velar stop, or "k", sound in Ancient Greek and Modern Greek....
or ?

Gamma

EC meter

Classification of materials by conductivity

A conductor
Electrical conductor

In science and Electrical engineering, an electrical conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons ....
such as a metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
has high conductivity and a low resistivity.
An insulator
Electrical insulation

An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons....
like glass
Glass

Glass generally refers to a Hardness, brittle, transparency amorphous solid, such as that used for windows, many Glass Bottles, or eyewear, including, but not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovite , or aluminium oxynitride....
or a vacuum
Vacuum

A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty," but in reality, no volume of space can ever be perfectly empty....
has low conductivity.
The conductivity of a semiconductor
Semiconductor

A semiconductor is a material that has electrical conductivity between those of a Electrical conductor and an electrical insulation; it can vary over that wide range either permanently or dynamically....
is generally intermediate, but varies widely under different conditions, such as exposure of the material to electric fields or specific frequencies of light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
, and, most important, with temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater 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

Water (molecule)

File:Blue-water-pool.jpgWater is the most abundant molecule on Earth's surface, constituting about 70% of the Earth's surface in liquid, solid, and gaseous states....
is highly dependent on its concentration

Concentration

In chemistry, concentration is the measure of how much of a given chemical 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 solute in the solvent....
of dissolved salts and sometimes other chemical species which tend to ionize

Ionization

Ionization is the physics process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions....
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", which is the conductivity of the water were it measured at 25 C.

Some electrical conductivities

	Electrical Conductivity (S·m^-1)	Temperature(°C)	Notes
Silver Silver Silver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal....	63.01 × 10⁶	20	Highest electrical (as well as thermal) conductivity of any known metal
Copper Copper Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....	59.6 × 10⁶	20
Annealed Annealing (metallurgy) Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness.... Copper Copper Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....	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.
Gold Gold Gold is a chemical element with the symbol Au and atomic number 79. It is a highly sought-after precious metal, having been used as money, as a store of value, in jewelry, in sculpture, and for ornamentation since the beginning of recorded history....	45.2 × 10⁶	20	Gold is commonly used in electrical contacts
Aluminum	37.8 × 10⁶	20
Sea water	4.788	20	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. 4.8(S·m^-1) would be for an average salinity of 35 g/kg at about 20(°C) Copyright on the linked material can be found here http://www.kayelaby.npl.co.uk/copyright/
Drinking water Drinking water Drinking water is water that is of sufficiently high quality so that it can be consumed or utilized without risk of immediate or long term harm....	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

Complex conductivity

To analyse the conductivity of materials exposed to alternating electric fields, it is necessary to treat conductivity as a complex number

Complex number

In mathematics, the complex numbers are an extension of the real numbers obtained by adjoining an imaginary unit, denoted i, which satisfies:...
(or as a matrix of complex numbers, in the case of anisotropic materials mentioned above) called the admittivity
Admittance

In electrical engineering, the admittance is the multiplicative inverse of the Electrical impedance . The SI unit of admittance is the siemens ....
. This method is used in applications such as electrical impedance tomography

Electrical impedance tomography

Electrical impedance tomography is a medical imaging technique in which an image of the conductivity or permittivity of part of the body is inferred from surface electrical measurements....
, a type of industrial and medical imaging

Medical imaging

Medical imaging refers to the techniques and processes used to create s of the human body for clinical purposes or medical science .As a discipline and in its widest sense, it is part of biological imaging and incorporates radiology , radiological sciences, endoscopy, thermography, medical photography and microscopy ....
. Admittivity is the sum of a real component called the conductivity and an imaginary component called the susceptivity

Susceptance

In electrical engineering, the susceptance is the imaginary part of the admittance. In SI units, the susceptance is measured in siemens . Oliver Heaviside first defined this property, which he called permittance, in June 1887....
.

An alternative description of the response to alternating currents uses a real (but frequency-dependent) conductivity, along with a real permittivity

Permittivity

Permittivity is a physical quantity that describes how an electric field affects, and is affected by a dielectric medium, and is determined by the ability of a material to polarization in response to the field, and thereby reduce the total electric field inside the material....
. The larger the conductivity is, the more quickly the alternating-current signal is absorbed by the material (i.e., the more opaque

Opacity (optics)

Opacity is the measure of impenetrability to electromagnetic radiation or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, radiation shield, glass, etc....
the material is). For details, see Mathematical descriptions of opacity

Mathematical descriptions of opacity

When an electromagnetic wave travels through a medium in which it get absorbed , as described by the Beer-Lambert law, there are a wide array of mathematical descriptions of the parameters involved in the propagation and attenuation of the wave....
.

Temperature dependence

Electrical conductivity is strongly dependent on temperature

Temperature

Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
s, electrical conductivity decreases with increasing temperature, whereas in semiconductor

Semiconductor

A semiconductor is a material that has electrical conductivity between those of a Electrical conductor and an electrical insulation; it can vary over that wide range either permanently or dynamically....
s, electrical conductivity increases with increasing temperature. Over a limited temperature range, the electrical conductivity can be approximated as being directly proportional

Proportionality (mathematics)

In mathematics, two quantity are called proportional if they vary in such a way that one of the quantities is a constant multiple of the other, or equivalently if they have a constant ratio....
to temperature

Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater 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

Slope

Slope is used to describe the steepness, incline, gradient, or grade of a line . A higher slope value indicates a steeper incline. The slope is defined as the ratio of the "rise" divided by the "run" between two points on a line, or in other words, the ratio of the altitude change to the horizontal distance between any two point...
in the conductivity-vs-temperature graph, which can be written as:

where

s_T′ is the electrical conductivity at a common temperature, T′

s_T is the electrical conductivity at a measured temperature, T

a 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

Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
s is about 2 %/°C, however it can range between (1 to 3) %/°C. This slope is influenced by the geochemistry

Geochemistry

The field of geochemistry involves study of the chemistry composition of the Earth and other planets, chemical processes and reactions that govern the composition of Rock s and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and their interaction with the hydrosphere and the atmosph...
, and can be easily determined in a laboratory

Laboratory

A laboratory is a facility that provides controlled conditions in which science research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories....
.

At extremely low temperatures (not far from absolute zero), a few materials have been found to exhibit very high electrical conductivity in a phenomenon called superconductivity

Superconductivity

Superconductivity is a phenomenon occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field ....
.

External links

Measurement Techniques, Definitions, Electrical conductivity Calculation from the Glass Composition

Electrical conductivity

Classification of materials by conductivity

Some electrical conductivities

Complex conductivity

Temperature dependence

See also

External links