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'''Classical electromagnetism''' or '''classical electrodynamics''' is a branch of [[theoretical physics]] that studies the interactions between [[electric charge]]s and [[electrical current|currents]] using an extension of the [[classical Newtonian model]]. It is, therefore, a [[classical field theory]]. The theory provides a description of electromagnetic phenomena whenever the relevant [[length scale]]s and field strengths are large enough that [[quantum mechanical]] effects are negligible. For small distances and low field strengths, such interactions are better described by [[quantum electrodynamics]] which is a [[quantum field theory]].
Fundamental physical aspects of classical electrodynamics are presented in many textbooks. For the undergraduate level, textbooks like ''[[The Feynman Lectures on Physics]]'', [[Electricity and Magnetism (book)|''Electricity and Magnetism'']], and ''[[Introduction to Electrodynamics]]'' are considered as classic references
== History ==
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where
Unfortunately, this definition has a caveat. From [[Maxwell's equations]], it is clear that {{nowrap|∇ × '''E'''}} is not always zero, and hence the scalar potential alone is insufficient to define the electric field exactly. As a result, one must add a correction factor, which is generally done by subtracting the time derivative of the '''A''' vector potential described below. Whenever the charges are quasistatic, however, this condition will be essentially met.
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Branches of classical electromagnetism such as optics, electrical and electronic engineering consist of a collection of relevant [[mathematical model]]s of different degrees of simplification and idealization to enhance the understanding of specific electrodynamics phenomena.<ref>[[Rudolf Peierls|Peierls]], Rudolf. Model-making in physics, Contemporary Physics, Volume 21 (1), January 1980, 3-17.</ref> An electrodynamics phenomenon is determined by the particular fields, specific densities of electric charges and currents, and the particular transmission medium. Since there are infinitely many of them, in modeling there is a need for some typical, representative
:(a) electrical charges and currents, e.g. moving pointlike charges and electric and magnetic dipoles, electric currents in a conductor etc.;
:(b) electromagnetic fields, e.g. voltages, the Liénard–Wiechert potentials, the monochromatic plane waves, optical rays
:(c) transmission media, e.g. electronic components, antennas, electromagnetic waveguides, flat mirrors, mirrors with curved surfaces convex lenses, concave lenses; resistors, inductors, capacitors, switches; wires, electric and optical cables, transmission lines, integrated circuits etc.; all of which have only few variable characteristics.
== See also ==
* [[Mathematical descriptions of the electromagnetic field]]
* [[Weber electrodynamics]]
* [[Wheeler–Feynman absorber theory]]
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