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In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. [1] The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point.
The upper graph shows the current density as function of the overpotential η . The anodic and cathodic current densities are shown as j a and j c, respectively for α=α a =α c =0.5 and j 0 =1mAcm −2 (close to values for platinum and palladium). The lower graph shows the logarithmic plot for different values of α (Tafel plot).
The two most significant results of the Drude model are an electronic equation of motion, = (+ ) , and a linear relationship between current density J and electric field E, =. Here t is the time, p is the average momentum per electron and q, n, m , and τ are respectively the electron charge, number density, mass, and mean free time between ...
We have previously derived the relationship between electron mobility and current density = + = (+) Now Ohm's law can be written in the form = where is defined as the conductivity. Therefore we can write down: σ = e n μ e + e p μ h {\displaystyle \sigma =en\mu _{e}+ep\mu _{h}} which can be factorised to σ = e ( n μ e + p μ h ...
The current density is parallel to the electric field by necessity. Conductivity is the inverse (reciprocal) of resistivity. ... Relation between current density and ...
This ongoing current in both directions is called the exchange current density. When the potential is set more negative than the formal potential, the cathodic current is greater than the anodic current. Written as a reduction, cathodic current is positive. The net current density is the difference between the cathodic and anodic current density.
The net electric current I is the surface integral of the electric current density J passing through Σ: =, where dS denotes the differential vector element of surface area S, normal to surface Σ. (Vector area is sometimes denoted by A rather than S , but this conflicts with the notation for magnetic vector potential ).
The drift velocity then determines the electric current density and its relationship to E and is independent of the collisions. Drude calculated the average drift velocity from p = − e E τ where p is the average momentum , − e is the charge of the electron and τ is the average time between the collisions.