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In electromagnetism, displacement current density is the quantity ∂D/∂t appearing in Maxwell's equations that is defined in terms of the rate of change of D, the electric displacement field. Displacement current density has the same units as electric current density, and it is a source of the magnetic field just as actual current is.
In physics, the electric displacement field (denoted by D), also called electric flux density or electric induction, is a vector field that appears in Maxwell's equations. It accounts for the electromagnetic effects of polarization and that of an electric field , combining the two in an auxiliary field .
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.
The primary quantity that characterizes the electronic structure of any crystalline material is the probability of photon absorption, which is directly related to the imaginary part of the optical dielectric function ε(ω). The optical dielectric function is given by the fundamental expression: [11]
angular displacement: radian (rad) kappa: torsion coefficient also called torsion constant newton meter per radian (N⋅m/rad) lambda: cosmological constant: per second squared (s −2) wavelength: meter (m) linear charge density: coulomb per meter (C/m) eigenvalue: non-zero vector
Derived quantity Symbol Description SI derived unit Dimension Comments Absement: A: Measure of sustained displacement: the first integral with respect to time of displacement m⋅s L T: vector Acceleration: a →: Rate of change of velocity per unit time: the second time derivative of position m/s 2: L T −2: vector Angular acceleration: ω a
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In electromagnetism, Jefimenko's equations (named after Oleg D. Jefimenko) give the electric field and magnetic field due to a distribution of electric charges and electric current in space, that takes into account the propagation delay (retarded time) of the fields due to the finite speed of light and relativistic effects.