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In many situations of interest to [[electrical engineering]], it is not necessary to apply quantum theory to get correct results. [[Classical physics]] is still an accurate approximation in most situations involving [[macroscopic]] objects. With few exceptions, quantum theory is only necessary at the [[atomic scale]] and a simpler classical treatment can be applied. Further simplifications of treatment are possible in limited situations. [[Electrostatics]] deals only with stationary [[electric charge]]s so magnetic fields do not arise and are not considered. [[Permanent magnet]]s can be described without reference to electricity or electromagnetism. [[Circuit theory]] deals with [[electrical network]]s where the fields are largely confined around current carrying [[Electrical conductor|conductors]]. In such circuits, even Maxwell's equations can be dispensed with and simpler formulations used. On the other hand, a quantum treatment of electromagnetism is important in [[chemistry]]. [[Chemical reaction]]s and [[chemical bond]]ing are the result of [[quantum mechanical]] interactions of [[electron]]s around [[atom]]s. Quantum considerations are also necessary to explain the behaviour of many electronic devices, for instance the [[tunnel diode]].
== Electric
[[File:CoulombsLaw-2.png|thumb|282x282px|Coulomb's law tells us that like charges repel and opposite charges attract.]]
Electromagnetism is one of the [[Fundamental interaction|fundamental forces of nature]] alongside [[gravity]], the [[Strong interaction|strong force]] and the [[Weak interaction|weak force]]. Whereas gravity acts on all things that have [[mass]], electromagnetism acts on all things that have [[electric charge]]. Furthermore, as there is the [[conservation of mass]] according to which mass cannot be created or destroyed, there is also the [[conservation of charge]] which means that the charge in a closed system (where no charges are leaving or entering) must remain constant.<ref name=":0">{{Cite book|last=Purcell, Edward M.|url=https://www.worldcat.org/oclc/805015622|title=Electricity and magnetism|date=21 January 2013|isbn=978-1-107-01402-2|edition=Third|___location=Cambridge|pages=3–4|oclc=805015622}}</ref> The fundamental law that describes the gravitational force on a massive object in [[classical physics]] is [[Newton's law of gravity]]. Analogously, [[Coulomb's law]] is the fundamental law that describes the force that charged objects exert on one another. It is given by the formula
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