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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.
Continuous charge distribution. The volume charge density ρ is the amount of charge per unit volume (cube), surface charge density σ is amount per unit surface area (circle) with outward unit normal nĚ‚, d is the dipole moment between two point charges, the volume density of these is the polarization density P.
Tesla coil, 0.76 meters (2 ft 6 in) high, at 200 kV and 270 kV peak [4] 2.1 A High power LED current (peak 2.7 A) [5] 5 A One typical 12 V motor vehicle headlight (typically 60 W) 9 A 230 V AC, toaster, kettle (2 kW) 10 1: 10 or 20 A 230 V AC, Europe common domestic circuit breaker rating 15 or 20 A
The plotted line represents the variation of instantaneous voltage (or current) with respect to time. This cycle repeats with a frequency that depends on the power system. In electrical engineering, three-phase electric power systems have at least three conductors carrying alternating voltages that are offset in time by one-third of the period ...
The current 3-form can be integrated over a 3-dimensional space-time region. The physical interpretation of this integral is the charge in that region if it is spacelike, or the amount of charge that flows through a surface in a certain amount of time if that region is a spacelike surface cross a timelike interval.
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 ...
In physics, there are equations in every field to relate physical quantities to each other and perform calculations. Entire handbooks of equations can only summarize most of the full subject, else are highly specialized within a certain field. Physics is derived of formulae only.
The displacement current is justified today because it serves several requirements of an electromagnetic theory: correct prediction of magnetic fields in regions where no free current flows; prediction of wave propagation of electromagnetic fields; and conservation of electric charge in cases where charge density is time-varying.