- In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases.
- In order for current to flow within a closed electrical circuit, it is not necessary for one charged particle to travel from the component producing the current (the current source) to those consuming it (the loads). Instead, the charged particle simply needs to nudge its neighbor a finite amount, who will nudge its neighbor, and on and on until a particle is nudged into the consumer, thus powering it. Essentially what is occurring is a long chain of momentum transfer between mobile charge carriers; the Drude model of conduction describes this process more rigorously. This momentum transfer model makes metal an ideal choice for a conductor; metals, characteristically, possess a delocalized sea of electrons which gives the electrons enough mobility to collide and thus affect a momentum transfer.
- As discussed above, electrons are the primary mover in metals; however, other devices such as the cationic electrolyte(s) of a battery, or the mobile protons of the proton conductor of a fuel cell rely on positive charge carriers. Insulators are non-conducting materials with few mobile charges that support only insignificant electric currents.
- Electrical conduction occurs through transport of electric charge in response to an applied electric field. Electric charge is carried by electrons, electron holes, and ions. Electrical conductivity σ and its reciprocal, electrical resistivity, ρ = 1/σ, are physical properties of a material. While the range of values is somewhat arbitrary, electrical conductivity is very low in insulators, σ < 10-15 S/cm (ρ > 1021 Ωcm), intermediate in semiconductors, σ = 10-5 to 103 S/cm (ρ = 103 - 1011 Ωcm), very high in conductors, σ = 104 to 106 S/cm (ρ = 1 - 102 µΩcm), and infinite in superconductors. Electrical conductivity,σ, is defined as the product of the number of charge carriers, n, the charge, e, and the mobility of the charge carriers, μ. σ = n ⋅ e ⋅ μ (1) For electronic conductors the electron charge, e = 1.6 x 10-19 coulombs, is constant and independent of temperature. The mobility, μ, usually decreases with increasing temperature due to collisions between the moving electrons and phonons, i.e., lattice vibrations. The number of charge carriers, n, remains constant for metallic conductors with increasing temperature, but increases exponentially for semiconductors and insulators. Thus at very high temperatures some insulators become semiconducting, while at low temperatures some semiconductors become insulators. Electronic conduction in a solid can be described in terms of the electronic band model. Quantum mechanics designates for each electron location probabilities as well as allowed energy levels also called electronic orbitals. Thus, an isolated atom represents a potential well with discrete electron energy levels. If two such atomic wells are brought into close proximity, then the isolated discrete energy levels split into a set of bonding and a set of antibonding levels. This is a consequence of the Pauli’s exclusion principle, which forbids any two electrons to occupy the same energy level (neglecting electron spin). When a very large number, N, of such wells are brought into close proximity, then the original discrete energy levels overlap into quasi-continuous broad bands, each of which comprises N energy levels.
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