Electrical conductivity is the ability of a body to conduct an electrical current. Electrical conductivity (σ) measures the ability of a material to pass an electric current through it and is inversely proportional to the material’s electrical resistance.
In the International System of Units (SI), the unit for measuring electrical conductivity is S / m (Siemens per meter) or Ω−1 · m−1.
The electrical conductivity will depend on the atomic and molecular structure of the material. In addition, conductivity is related to the ability of charged particles (electrons, positive or negative ions) contained in this medium to move freely enough.
According to Ohm's law, in a linear isotropic substance, conductivity is the coefficient of proportionality between the density of the resulting current and the magnitude of the electric field in the medium.
Electrical conductivity is the reciprocal of electrical resistivity.
Why do metals conduct electricity?
Metals are good electrical conductors because electrons are delocalized around positively charged nuclei. Metallic bonding explains many properties of metals. In metals, the electrons are free to move and carry a charge.
Conductivity also depends on its chemical composition and other physical factors of the material itself, such as temperature, length, and cross-section area.
All materials have positive particles called protons and negative particles called electrons in their atoms. All metals have such a stable atomic structure that electrons are free to move smoothly through the cross-sectional area when electricity contacts this material.
Metals conduct electricity because they are made up of a cluster of positively charged nuclei between which electrons move freely. Pure metals tend to provide the best conductivity. In most metals, the existence of impurities restricts the flow of electrons.
This cloud of free electrons does not belong to individual atoms but rather to all of them. This model explains why metals conduct electricity.
Why aren’t insulators good electrical conductors?
The low electrical conductivity of insulators is due to the properties of the valence band in which electrons cannot move.
In electrical insulators, the number of electrons is the same as the number of states available in the valence band. In the forbidden band, there are no electronic states available. When an electric field is applied, the electrons cannot increase their speed as there are no available states where they can move faster than they already do.
Compounds with covalent bonds do not conduct electricity because they do not have charged particles capable of transporting electrons. Lewis’s theory also accounts for bond length; the more robust the bond and the more electrons shared, the shorter the bond length is.
A valence electron is an outer shell electron that is associated with an atom. It can be part of the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, both particles contribute one valence electron to form a shared pair.
Electrical conductivity and current carriers
The electrical conductivity of all substances is associated with the presence of current carriers. Current carriers are moving electric charges (electrons, ions) or quasiparticles. Carriers can move in a substance over a long distance.
It means that such a particle or quasiparticle should be able to travel in a given substance at an infinitely large distance. However, in some exceptional cases, the carriers can change, be born and disappear, and replace each other.
Examples of specific electrical conductivity of some substances
In electrical engineering, it is crucial to be aware of the specific electrical conductivity of each material. Silver and copper have a high electrical conductivity being silver which has the highest conductivity. Silver defines conductivity - all other metals are compared against it.
Specific conductivity is given at a temperature of +20 ° C:
|
Substance |
S / m |
|
silver |
62,500,000 |
|
copper |
59,500,000 |
|
gold |
45,500,000 |
|
aluminum |
38,000,000 |
|
pure iron |
10,000,000 |
|
tin |
8,330,000 |
|
cast steel |
7,690,000 |
|
mercury |
1,040,000 |
|
graphite |
125,000 |
|
seawater |
3 |
|
pure water. |
10 −4 |
|
glass |
10 −11 |