displacement current

displacement current [dis′plās·mənt ‚kə·rənt]

(electromagnetism)

The rate of change of the electric displacement vector, which must be added to the current density to extend Ampère's law to the case of time-varying fields (meter-kilogram-second units). Also known as Maxwell's displacement current.

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Displacement current

The name given by J. C. Maxwell to the term ∂ D /∂t which must be added to the current density i to extend to time-varying fields the magnetostatic result of A. M. Ampère that i equals the curl of the magnetic intensity H . In integral form this result is given by the equation below,

where the unit vector n is perpendicular to the surface dS. The concept of displacement current has important consequences for insulators and for free space where i vanishes. For conductors, however, the difference between the above equation and Ampère's result is negligible. See Maxwell's equations

If one defines current as a transport of charge, the term displacement current is certainly a misnomer when applied to a vacuum where no charges exist. If, however, current is defined in terms of the magnetic fields it produces, the expression is legitimate.