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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.
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 ...
If the magnetic field is constant, the magnetic flux passing through a surface of vector area S is = = , where B is the magnitude of the magnetic field (the magnetic flux density) having the unit of Wb/m 2 , S is the area of the surface, and θ is the angle between the magnetic field lines and the normal (perpendicular) to S.
vector Current density: J →: Electric current per unit cross-section area A/m 2: L −2 I: conserved, intensive, vector Electric dipole moment: p: Measure of the separation of equal and opposite electric charges C⋅m L T I: vector Electric displacement field: D →: Strength of the electric displacement C/m 2: L −2 T I: vector field ...
For vector flux, the surface integral of j over a surface S, gives the proper flowing per unit of time through the surface: = ^ =, where A (and its infinitesimal) is the vector area – combination = ^ of the magnitude of the area A through which the property passes and a unit vector ^ normal to the area. Unlike in the second set of equations ...
The magnetic vector potential, , is a vector field, and the electric potential, , is a scalar field such that: [5] = , =, where is the magnetic field and is the electric field. In magnetostatics where there is no time-varying current or charge distribution , only the first equation is needed.
The most common description of the electromagnetic field uses two three-dimensional vector fields called the electric field and the magnetic field. These vector fields each have a value defined at every point of space and time and are thus often regarded as functions of the space and time coordinates.
A distribution of magnetic current, commonly called a magnetic frill generator, may be used to replace the driving source and feed line in the analysis of a finite diameter dipole antenna. [ 4 ] : 447–450 The voltage source and feed line impedance are subsumed into the magnetic current density.