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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.
In special and general relativity, the four-current (technically the four-current density) [1] is the four-dimensional analogue of the current density, with units of charge per unit time per unit area. Also known as vector current, it is used in the geometric context of four-dimensional spacetime, rather than separating time from three ...
Electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typically denoted as either () or ().
where this time is the charge density, is the current density vector, and is the current source-sink term. The current source and current sinks are where the current density emerges σ > 0 {\displaystyle \sigma >0} or vanishes σ < 0 {\displaystyle \sigma <0} , respectively (for example, the source and sink can represent the two poles of an ...
Current density is the rate at which charge passes through a chosen unit area. [25]: 31 It is defined as a vector whose magnitude is the current per unit cross-sectional area. [2]: 749 As discussed in Reference direction, the direction is arbitrary. Conventionally, if the moving charges are positive, then the current density has the same sign ...
where is the charge density, which is a function of time and position, is the vacuum permittivity, is the vacuum permeability, and J is the current density vector, also a function of time and position. Inside a linear material, Maxwell's equations change by switching the permeability and permittivity of free space with the permeability and ...
where E is the electric field vector with units of volts per meter (analogous to V of Ohm's law which has units of volts), J is the current density vector with units of amperes per unit area (analogous to I of Ohm's law which has units of amperes), and ρ "rho" is the resistivity with units of ohm·meters (analogous to R of Ohm's law which has ...
scalar Angular acceleration: ω a: Change in angular velocity per unit time rad/s 2: T −2: Area: A: Extent of a surface m 2: L 2: extensive, bivector or scalar Area density: ρ A: Mass per unit area kg⋅m −2: L −2 M: intensive Capacitance: C: Stored charge per unit electric potential farad (F = C/V) L −2 M −1 T 4 I 2: scalar ...