Editing Displacement current (section)

{{Short description|Physical quantity in electromagnetism}}
{{About-distinguish|electric displacement current|magnetic displacement current}}
{{Use American English|date = March 2019}}
{{electromagnetism|cTopic=Electrodynamics}}
In [[electromagnetism]], '''displacement current density''' is the quantity {{math|&part;'''D'''/&part;''t''}} appearing in [[Maxwell's equations]] that is defined in terms of the rate of change of {{math|'''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. However it is not an electric current of moving [[Electric charge|charges]], but a time-varying [[electric field]].  In physical materials (as opposed to vacuum), there is also a contribution from the slight motion of charges bound in atoms, called [[dielectric polarization]].

The idea was conceived by [[James Clerk Maxwell]] in his 1861 paper ''[https://books.google.com/books?id=v1YEAAAAYAAJ&pg=PA14 On Physical Lines of Force, Part III]'' in connection with the displacement of electric particles in a [[dielectric]] medium. Maxwell added displacement current to the [[electric current]] term in [[Ampère's circuital law]].  In his 1865 paper [[A Dynamical Theory of the Electromagnetic Field]] Maxwell used this amended version of Ampère's circuital law to derive the [[electromagnetic wave equation]]. This derivation is now generally accepted as a historical landmark in physics by virtue of uniting electricity, magnetism and optics into one single unified theory.  The displacement current term is now seen as a crucial addition that completed Maxwell's equations and is necessary to explain many phenomena, most particularly the existence of [[electromagnetic wave]]s.