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Charge carrier density, also known as carrier concentration, denotes the number of charge carriers per volume. In SI units, it is measured in m −3. As with any density, in principle it can depend on position. However, usually carrier concentration is given as a single number, and represents the average carrier density over the whole material.
In electromagnetism, charge density is the amount of electric charge per unit length, surface area, or volume. Volume charge density (symbolized by the Greek letter ρ) is the quantity of charge per unit volume, measured in the SI system in coulombs per cubic meter (C⋅m −3), at any point in a volume.
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.
For negative charges, the sign of the current density is opposite to the velocity of the charges. [2]: 749 In SI units, current density (symbol: j) is expressed in the SI base units of amperes per square metre. [4]: 22 In linear materials such as metals, and under low frequencies, the current density across the conductor surface is uniform.
The electron mobility is defined by the equation: =. where: E is the magnitude of the electric field applied to a material,; v d is the magnitude of the electron drift velocity (in other words, the electron drift speed) caused by the electric field, and
In operating batteries and fuel cells, charge transfer coefficient is the parameter that signifies the fraction of overpotential that affects the current density. This parameter has had a mysterious significance in electrochemical kinetics for over three quarters of the previous century [citation needed]. It can also be said that charge ...
The current in a wire is the velocity of the electrons multiplied by the charge and number per unit length, = / or = /. This gives a conductance of G = v e 2 N / L E {\displaystyle G=ve^{2}\!N/LE} . In nano scale bridges the conductance falls in discrete steps of multiples of the quantum conductance G = 2 e 2 / h {\displaystyle G=2\,e^{2}\!/h} .
In electronics, the relationship between the direct current (DC) through an electronic device and the DC voltage across its terminals is called a current–voltage characteristic of the device. Electronic engineers use these charts to determine basic parameters of a device and to model its behavior in an electrical circuit .