Displacement current density

Displacement current density is the vector contribution of a changing electric field to magnetic-field generation, expressed as current per unit area. It is defined by the time rate of change of electric displacement.

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Maxwell–Ampère law: A Maxwell equation relating magnetic fields to conduction current and changing electric displacement. It places displacement current density alongside conduction current as a source of magnetic circulation.
Electric current density: A vector quantity measuring electric current crossing a unit area. Displacement current density shares its units and current-per-area interpretation.
Capacitor: An electrical component that stores energy in an electric field between conductors. Between its plates, changing electric displacement accounts for magnetic effects despite the insulating gap.
James Clerk Maxwell: A Scottish physicist who unified electricity, magnetism, and light in classical field theory. Maxwell introduced the displacement-current term to complete the magnetic-field equation.
Electric displacement field: A vector field describing electric flux density, including polarization effects in matter. Displacement current density is the time derivative of this field.
Electric permittivity: A property relating an electric field to electric displacement in a medium. In a linear isotropic medium, permittivity relates the field change to displacement current density.
Charging capacitor: A capacitor receiving charge from an external circuit, causing its electric field to change over time. Its gap illustrates how displacement current density keeps the magnetic-field law consistent across a circuit.
Maxwell's Treatise on Electricity and Magnetism: James Clerk Maxwell’s 1873 two-volume work presenting his theory of electromagnetism. The treatise developed the theoretical framework that includes displacement current.
Maxwell's equations: Four equations that describe classical electromagnetism and its relation to charge and current. They establish the broader field equations in which displacement current density appears.
Vacuum permittivity: The electric permittivity of empty space, a constant in electromagnetic equations. It sets the proportionality between changing electric field and displacement current density in vacuum.