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  2. Current density - Wikipedia

    en.wikipedia.org/wiki/Current_density

    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.

  3. Sources and sinks - Wikipedia

    en.wikipedia.org/wiki/Sources_and_sinks

    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 ...

  4. Four-current - Wikipedia

    en.wikipedia.org/wiki/Four-current

    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 ...

  5. Maxwell's equations - Wikipedia

    en.wikipedia.org/wiki/Maxwell's_equations

    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 ).

  6. Ohm's law - Wikipedia

    en.wikipedia.org/wiki/Ohm's_law

    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 ...

  7. Electric current - Wikipedia

    en.wikipedia.org/wiki/Electric_current

    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 ...

  8. Electromagnetic field - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_field

    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 ...

  9. Continuity equation - Wikipedia

    en.wikipedia.org/wiki/Continuity_equation

    The density of a quantity ρ and its current j can be combined into a 4-vector called a 4-current: = (,,,) where c is the speed of light. The 4- divergence of this current is: ∂ μ J μ = c ∂ ρ ∂ c t + ∇ ⋅ j {\displaystyle \partial _{\mu }J^{\mu }=c{\frac {\partial \rho }{\partial ct}}+\nabla \cdot \mathbf {j} } where ∂ μ is the 4 ...