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The drift current, by contrast, is due to the motion of charge carriers due to the force exerted on them by an electric field. Diffusion current can be in the same or opposite direction of a drift current. The diffusion current and drift current together are described by the drift–diffusion equation. [1]
The drift velocity is the average velocity of the charge carriers in the drift current. The drift velocity, and resulting current, is characterized by the mobility; for details, see electron mobility (for solids) or electrical mobility (for a more general discussion). See drift–diffusion equation for the way that the drift current, diffusion ...
This diffusion current is governed by Fick's law: = where: F is flux. D e is the diffusion coefficient or diffusivity; is the concentration gradient of electrons; The diffusion coefficient for a charge carrier is related to its mobility by the Einstein relation.
In physics, the motion of an electrically charged particle such as an electron or ion in a plasma in a magnetic field can be treated as the superposition of a relatively fast circular motion around a point called the guiding center and a relatively slow drift of this point. The drift speeds may differ for various species depending on their ...
In other words, the electrical mobility of the particle is defined as the ratio of the drift velocity to the magnitude of the electric field: =. For example, the mobility of the sodium ion (Na + ) in water at 25 °C is 5.19 × 10 −8 m 2 /(V·s) . [ 1 ]
The formula for evaluating the drift velocity of charge carriers in a material of constant cross-sectional area is given by: [1] =, where u is the drift velocity of electrons, j is the current density flowing through the material, n is the charge-carrier number density, and q is the charge on the charge-carrier.
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In electromagnetism, displacement current density is the quantity ∂D/∂t appearing in Maxwell's equations that is defined in terms of the rate of change of D, the electric displacement field. Displacement current density has the same units as electric current density, and it is a source of the magnetic field just as actual