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The theoretical implications of electromagnetism led to the development of [[special relativity]] by [[Albert Einstein]] in [[1905]].
 
== The electromagnetic force ==
{{main|Electromagnetic force}}
The force that the electromagnetic field exerts on electrically charged particles, called the '''electromagnetic force''', is one of the four [[fundamental force]]s. The other fundamental forces are the [[strong interaction|strong nuclear force]] (which holds [[atomic nucleus|atomic nuclei]] together), the [[weak interaction|weak nuclear force]] (which causes certain forms of [[radioactive decay]]), and the [[gravity|gravitational force]]. All other forces are ultimately derived from these fundamental forces.
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As it turns out, the electromagnetic force is the one responsible for practically all the phenomena encountered in daily life, with the exception of gravity. Roughly speaking, all the forces involved in interactions between [[atom]]s can be traced to the electromagnetic force acting on the electrically charged [[proton]]s and [[electron]]s inside the atoms. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the [[intermolecular force]]s between the individual [[molecule]]s in our bodies and those in the objects. It also includes all forms of [[chemistry|chemical phenomena]], which arise from interactions between [[Molecular orbital|electron orbitals]].
 
== Classical electrodynamics ==
The scientist [[William Gilbert]] proposed, in his ''[[De Magnete]]'' ([[1600]]), that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects. Mariners had noticed that lightning strikes had the ability to disturb needle, but the link between lightning and electricity was not confirmed until [[Benjamin Franklin]]'s proposed experiments in [[1752]]. One of the first to discover and publish a link between man-made electric current and magnetism was [[Gian Domenico Romagnosi|Romagnosi]], who in [[1802]] noticed that connecting a wire across a [[Voltaic pile]] deflected a nearby [[compass]] needle. However, the effect did not become widely known until [[1820]], when [[Hans Christian Ørsted|Ørsted]] performed a similar experiment. Ørsted's work influenced [[André-Marie Ampère|Ampère]] to produce a theory of electromagnetism that set the subject on a mathematical foundation.
 
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In addition, relativity theory shows that in moving frames of reference a magnetic field transforms to a field with a nonzero electric component and vice versa; thus firmly showing that they are two sides of the same coin, and thus the term "electromagnetism".
 
== The photoelectric effect ==
In another paper published in that same year, Albert Einstein undermined the very foundations of classical electromagnetism. His theory of the [[photoelectric effect]] (for which he won the Nobel prize for physics) posited that light could exist in discrete particle-like quantities, which later came to be known as [[photon]]s. Einstein's theory of the photoelectric effect extended the insights that appeared in the solution of the [[ultraviolet catastrophe]] presented by [[Max Planck]] in [[1900]]. In his work, Planck showed that hot objects emit [[electromagnetic radiation]] in discrete packets, which leads to a finite total [[energy]] emitted as [[black body radiation]]. Both of these results were in direct contradiction with the classical view of light as a continuous wave. Planck's and Einstein's theories were progenitors of [[quantum mechanics]], which, when formulated in [[1925]], necessitated the invention of a quantum theory of electromagnetism. This theory, completed in the [[1940s]], is known as [[quantum electrodynamics]] (or "QED"), and is one of the most accurate theories known to physics.
 
== Definition ==
The term [[electrodynamics]] is sometimes used to refer to the combination of electromagnetism with [[mechanics]], and deals with the effects of the electromagnetic field on the dynamic behavior of electrically charged particles.
 
== Units ==
'''Electromagnetic units''' are part of a system of electrical units based primarily upon the magnetic properties of electric currents, the fundamental cgs unit being the abampere. The units are:
 
* [[ampere]] (current)
* [[coulomb]] (charge)
* [[farad]] (capacitance)
* [[henry_henry (unit)|henry]] (inductance)
* [[ohm]] (resistance)
* [[volt]] (electric potential)
* [[watt]] (power)
 
In the electromagnetic cgs system, electrical current is a fundamental quantity defined via [[Ampère's law]] and takes the [[Permeability (electromagnetism)|permeability]] as a dimensionless quantity (relative permeability) whose value in a vacuum is unity. As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.
{{SI_electromagnetism_units}}
 
== See also ==
<div class="references-small" style="-moz-column-count:4; column-count:4;">
* [[Abraham-Lorentz force]]
* [[Classical electromagnetism]]
* [[Double-slit experiment]]
* [[Electricity]]
* [[Electromagnet]]
* [[Electromagnetic modeling]]
* [[Electromagnetic wave equation]]
* [[Electromechanics]]
* [[Electrostatics]]
* [[Formulation of Maxwell's equations in special relativity]]
* [[Gamma ray]]
* [[Lorentz force]]
* [[Maglev]] <!--yes, the disambig page; both articles can be relevant to electromagneticism.-->
* [[Magnetism]]
* [[Maxwell's equations in curved spacetime]]
* [[Microwave]]
* [[Optics]]
* [[Photon polarization]]
* [[Plasma (physics)]]
* [[Polarization]]
* [[Radio wave]]
* [[Waveguide]]
* [[X-ray]]
</div>
 
== References ==
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See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for a
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