Definition and Concept of Displacement Current
– Displacement current is defined as the rate of change of the electric displacement field.
– It has the same units as electric current density and is a source of the magnetic field.
– Displacement current is not an electric current of moving charges, but a time-varying electric field.
– In physical materials, there is also a contribution from the slight motion of charges bound in atoms, called dielectric polarization.
– James Clerk Maxwell conceived the idea of displacement current in his 1861 paper.
Derivation and Importance of Displacement Current
– Maxwell added displacement current to Ampère’s Circuital Law to derive the electromagnetic wave equation.
– This derivation is considered a historical landmark in physics, as it unified electricity, magnetism, and optics into one theory.
– The displacement current term completed Maxwell’s equations and explained the existence of electromagnetic waves.
– Displacement current is crucial for explaining many phenomena in electromagnetism.
– It is necessary to account for the behavior of electric and magnetic fields.
Explanation of Electric Displacement Field
– The electric displacement field (D) is defined as the sum of the permittivity of free space (ε0) times the electric field intensity (E) and the polarization of the medium (P).
– The displacement current density (Jd) has two components: the rate of change of the electric field (dE/dt) and the rate of change of polarization (dP/dt).
– The first term on the right-hand side is present in material media and in free space, contributing to the magnetic field.
– The second term, called polarization current density, comes from the change in polarization of the dielectric material.
– The displacement current can be expressed as the time derivative of the electric flux.
Necessity and Applications of Displacement Current
– The displacement current is necessary to explain various phenomena observed in electromagnetism.
– It agrees with experimental observations and ensures logical consistency in the theory of electromagnetism.
– The displacement current is crucial for understanding the behavior of capacitors without a medium between the plates.
– It explains the existence of a magnetic field between the plates of a charging capacitor.
– The displacement current extends the notion of current beyond the transport of charge.
Relationship with Ampère’s Law, Wave Propagation, Historical Significance, and Applications
– Displacement current is included in Ampère’s law to ensure its consistency with the conservation of charge.
– The inclusion of displacement current allows Ampère’s law to correctly predict the magnetic field in situations where only changing electric fields are present.
– Displacement current plays a crucial role in the propagation of electromagnetic waves.
– James Clerk Maxwell introduced the concept of displacement current in his 1861 paper on electromagnetism.
– The understanding of displacement current is crucial in the design and analysis of circuits involving capacitors and the propagation of electromagnetic waves.
– Displacement current is a key concept in the field of optics and has applications in telecommunications, wireless technologies, and the development of electromagnetic devices and systems. Source: https://en.wikipedia.org/wiki/Displacement_current
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. However it is not an electric current of moving 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 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 waves.
