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{{Short description|Fundamental physical law – electric charge is continuously conserved in space and time}}
{{about|the conservation of electric charge|a general theoretical concept|charge (physics)}}
In [[physics]], '''charge conservation''' is the principle that the total [[electric charge]] in an [[isolated system]] never changes.<ref name=PurcellMorin>{{Cite book
| last = Purcell
| first = Edward M.
| author2 = Morin, David J.
| year = 2013
| title = Electricity and magnetism
| edition = 3rd
| publisher = Cambridge University Press
| isbn = 9781107014022
| pages = 4
}}</ref> The net quantity of electric charge, the amount of [[positive charge]] minus the amount of [[negative charge]] in the universe, is always ''[[Conserved quantity|conserved]]''. Charge conservation, considered as a [[conservation law (physics)|physical conservation law]], implies that the change in the amount of electric charge in any volume of space is exactly equal to the amount of charge flowing into the volume minus the amount of charge flowing out of the volume. In essence, charge conservation is an accounting relationship between the amount of charge in a region and the flow of charge into and out of that region, given by a [[continuity equation]] between [[charge density]] <math>\rho(\mathbf{x})</math> and [[current density]] <math>\mathbf{J}(\mathbf{x})</math>.
This does not mean that individual positive and negative charges cannot be created or destroyed. Electric charge is carried by [[subatomic particle]]s such as [[electron]]s and [[proton]]s. [[Charged particle|Charged particles]] can be created and destroyed in elementary particle reactions. In [[particle physics]], charge conservation means that in reactions that create charged particles, equal numbers of positive and negative particles are always created, keeping the net amount of charge unchanged. Similarly, when particles are destroyed, equal numbers of positive and negative charges are destroyed. This property is supported without exception by all empirical observations so far.<ref name="PurcellMorin" />
Although conservation of charge requires that the total quantity of charge in the universe is constant, it leaves open the question of what that quantity is. Most evidence indicates that the net charge in the universe is zero;<ref>
{{cite journal
|author1=S. Orito
|author2=M. Yoshimura
|journal=Physical Review Letters
|volume=54
|issue=22
|year=1985
|pages=2457–2460
|title=Can the Universe be Charged?
|doi=10.1103/PhysRevLett.54.2457
|pmid=10031347
|bibcode=1985PhRvL..54.2457O
}}</ref><ref>
{{cite journal
|author1=E. Masso |author2=F. Rota |journal=Physics Letters B
|volume=545
|issue=3–4
|year=2002
|pages=221–225
|title=Primordial helium production in a charged universe
|arxiv=astro-ph/0201248
|doi=10.1016/S0370-2693(02)02636-9|bibcode = 2002PhLB..545..221M |s2cid=119062159 }}</ref> that is, there are equal quantities of positive and negative charge.
==History==
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