![]() However, this effect is generally small, on the order of 10 −6. Such an expansion (or contraction) will change the geometry of the conductor and therefore its characteristic resistance. The amount that the material will expand is governed by the thermal expansion coefficient specific to the material. Temperature affects conductors in two main ways, the first is that materials may expand under the application of heat. At commercial power frequency, these effects are significant for large conductors carrying large currents, such as busbars in an electrical substation, or large power cables carrying more than a few hundred amperes.Īside from the geometry of the wire, temperature also has a significant effect on the efficacy of conductors. Similarly, if two conductors are near each other carrying AC current, their resistances increase due to the proximity effect. Then, the geometrical cross-section is different from the effective cross-section in which current actually flows, so the resistance is higher than expected. However, this formula still provides a good approximation for long thin conductors such as wires.Īnother situation this formula is not exact for is with alternating current (AC), because the skin effect inhibits current flow near the center of the conductor. This formula is not exact: It assumes the current density is totally uniform in the conductor, which is not always true in practical situation. ![]() Resistivity is a measure of the material's ability to oppose electric current. The resistance R and conductance G of a conductor of uniform cross section, therefore, can be computed as R = ρ ℓ A, G = σ A ℓ. Also, for a given material, the resistance is proportional to the length for example, a long copper wire has higher resistance than an otherwise-identical short copper wire. For example, a thick copper wire has lower resistance than an otherwise-identical thin copper wire. For a given material, the resistance is inversely proportional to the cross-sectional area. The resistance of a given conductor depends on the material it is made of, and on its dimensions. Main article: Electrical resistance and conductance Insulators are non-conducting materials with few mobile charges that support only insignificant electric currents. 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.Īs 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. ![]() 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. 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. 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). Electric current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases. Materials made of metal are common electrical conductors. ![]() 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. ![]()
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