Electric charge: Difference between revisions

Fix errors: Charge is supposed to be represented with a lowercase q not a uppercase Q
m (Reverted edits by Snowdrift on the Cloud Edge (talk) to last version by CLCStudent)
(Fix errors: Charge is supposed to be represented with a lowercase q not a uppercase Q)
Tag: 2017 wikitext editor
| unit = [[coulomb]]
| otherunits = {{Unbulleted list|[[elementary charge]]|[[Faraday constant|faraday]]|[[ampere-hour]]}}
| symbols = ''Qq''
| baseunits = C = A s
| dimension = '''T''' '''I'''
An electric charge has an [[electric field]], and if the charge is moving it also generates a [[magnetic field]]. The combination of the electric and magnetic field is called the [[electromagnetic field]], and its interaction with charges is the source of the [[electromagnetic force]], which is one of the four [[fundamental interaction|fundamental forces]] in [[physics]]. The study of [[photons|photon]]-mediated interactions among charged particles is called [[quantum electrodynamics]].
The [[SI derived unit]] of electric charge is the [[coulomb]] (C) named after French physicist [[Charles-Augustin de Coulomb]]. In [[electrical engineering]], it is also common to use the [[ampere-hour]] (Ah); in [[physics]] and [[chemistry]], it is common to use the elementary charge (''e'' as a unit). Chemistry also uses the [[Faraday constant]] as the charge on a [[mole (unit)|mole]] of electrons. The lowercase symbol ''Qq'' often denotes charge.
The [[International System of Units|SI]] derived unit of [[quantity]] of electric charge is the [[coulomb]] (symbol: C). The coulomb is defined as the quantity of charge that passes through the [[cross section (geometry)|cross section]] of an [[electrical conductor]] carrying one [[ampere]] for one [[second]].<ref name=CIPM1946>{{cite web |url=https://www.bipm.org/en/CIPM/db/1946/2/ |publisher=BIPM |title=CIPM, 1946: Resolution 2}}</ref> This unit was proposed in 1946 and ratified in 1948.<ref name=CIPM1946/> In modern practice, the phrase "amount of charge" is used instead of "quantity of charge".<ref name=SIBrochure>{{SIbrochure8th}}, p. 150</ref> The amount of charge in 1 electron ([[elementary charge]]) is approximately {{val|1.6|e=-19|u=C}}, and 1 coulomb corresponds to the amount of charge for about {{val|6.24|e=18|u=electrons}}. The lowercase symbol ''Qq'' is often used to denote a quantity of electricity or charge. The quantity of electric charge can be directly measured with an [[electrometer]], or indirectly measured with a [[galvanometer|ballistic galvanometer]].
After finding the [[charge quantization|quantized]] character of charge, in 1891 [[George Johnstone Stoney|George Stoney]] proposed the unit 'electron' for this fundamental unit of electrical charge. This was before the discovery of the particle by [[J. J. Thomson]] in 1897. The unit is today treated as nameless, referred to as {{em|elementary charge}}, {{em|fundamental unit of charge}}, or simply as {{em|e}}. A measure of charge should be a multiple of the elementary charge ''e'', even if at [[macroscopic scale|large scales]] charge seems to behave as a [[real number|real quantity]]. In some contexts it is meaningful to speak of fractions of a charge; for example in the charging of a [[capacitor]], or in the [[fractional quantum Hall effect]].
Thus, the conservation of electric charge, as expressed by the continuity equation, gives the result:
:<math>I = -\frac{\mathrm{d}Qq}{\mathrm{d}t}.</math>
The charge transferred between times <math>t_\mathrm{i}</math> and <math>t_\mathrm{f}</math> is obtained by integrating both sides:
:<math>Qq = \int_{t_{\mathrm{i}}}^{t_{\mathrm{f}}} I\, \mathrm{d}t </math>
where ''I'' is the net outward current through a closed surface and ''Qq'' is the electric charge contained within the volume defined by the surface.
==Relativistic invariance==
Aside from the properties described in articles about [[electromagnetism]], charge is a [[theory of relativity|relativistic]] [[charge invariance|invariant]]. This means that any particle that has charge ''Qq'', no matter how fast it goes, always has charge ''Qq''. This property has been experimentally verified by showing that the charge of ''one'' [[helium]] [[atomic nucleus|nucleus]] (two [[proton]]s and two [[neutron]]s bound together in a nucleus and moving around at high speeds) is the same as ''two'' [[deuterium]] nuclei (one proton and one neutron bound together, but moving much more slowly than they would if they were in a helium nucleus).<ref>{{cite journal|url=https://www.degruyter.com/downloadpdf/j/zna.1999.54.issue-10-11/zna-1999-10-1113/zna-1999-10-1113.pdf|title=Relativistic invariance of electric charge|last= Jefimenko |first=O.D.|date=1999|journal=Zeitschrift für Naturforschung A |volume=54 |issue=10–11|pages= 637–644 |doi=10.1515/zna-1999-10-1113|access-date=11 April 2018|bibcode=1999ZNatA..54..637J}}</ref><ref>{{cite web|url=https://physics.stackexchange.com/questions/248688/how-can-we-prove-charge-invariance-under-lorentz-transformation|title=How can we prove charge invariance under Lorentz Transformation?|website=physics.stackexchange.com|access-date=2018-03-27}}</ref><ref>{{cite journal|date=1992|last=Singal|first=A.K.|title=On the charge invariance and relativistic electric fields from a steady conduction current|url=|journal=Physics Letters A|language=en|volume=162|issue=2|pages=91–95|doi=10.1016/0375-9601(92)90982-R|issn=0375-9601|bibcode=1992PhLA..162...91S}}</ref>
==See also==