Electrical conduction: Difference between revisions
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In linear [[anisotropy|anisotropic]] materials, ''σ'', ''ρ'' and ''D'' are [[tensor]]s. |
In linear [[anisotropy|anisotropic]] materials, ''σ'', ''ρ'' and ''D'' are [[tensor]]s. |
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==Electrolytes== |
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Electric currents in [[electrolyte]]s are flows of electrically charged [[atom]]s ([[ion]]s). For example, if an electric field is placed across a solution of [[sodium|Na]]<sup>+</sup> and [[chlorine|Cl]]<sup>–</sup>, the sodium ions move towards the negative electrode (cathode), while the chloride ions move towards the positive electrode (anode). If conditions are right, reactions take place at the electrode surfaces which release electrons from the chloride and transfer electrons to the sodium.{{Dubious|date=September 2010}} |
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Water-ice and certain solid electrolytes called [[proton conductor]]s contain positive hydrogen ions or "[[protons]]" which are mobile. In these materials, electric currents are composed of moving protons, as opposed to the moving electrons found in [[metal]]s. |
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In certain electrolyte mixtures, populations of brightly-colored ions form the moving electric charges. The slow migration of these ions during an electric current is one example of a situation where a current is directly visible to human eyes. |
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[[File:Example.jpg]] |
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==References== |
==References== |
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Revision as of 11:49, 12 November 2010
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Electrical conduction is the movement of electrically charged particles through a transmission medium (electrical conductor). The movement of charge constitutes an electric current. This charge transport may reflect a potential difference due to an electric field, or a concentration gradient in carrier density. The latter reflects diffusion of the charge carriers. The physical parameters governing this transport depend upon the material.
Conduction in metals and resistors follows Ohm's Law. This states that the current is proportional to the applied electric field. Current density (current per unit area) J in a material is measured by the conductivity σ, defined as:
- J = σ E
or its reciprocal resistivity ρ:
- J = E / ρ
Conduction in semiconductor devices may occur by a combination of electric field (drift) and diffusion. The current density is then:
with q the elementary charge and n the electron density. The carriers move in the direction of decreasing concentration, so for electrons a positive current results for a positive density gradient. If the carriers are holes, replace electron density n by the negative of the hole density p.
In linear anisotropic materials, σ, ρ and D are tensors.
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