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DCCurrentLinearCircuits
1.1.Definitions&Terminology
Anelectricchargeisaphysicalpropertyofelectronsandprotonsofmattergives
risetoforcesbetweenatoms.ThechargeQunitisCoulomb[C].Protonshave
apositivechargesign(definition),electrons-negative.Respectively:+1.601i10-19C
and-1.601i10-19C.
Theelectriccurrenti(t)is“theflow”ofcharge-meansintheshapeofthe
waveastimefunction→()
it
±
dq
.Thebasicvalueofcurrentismeasuredin
dt
amps.Consequently,thechargeisdefinedas:
Q
±∫
t
t
2
1
itdt
()
[C]
(1.1)
Thechargepotentialdifferencebetweenthepoints(Fig.1.1)isdefinedasthe
voltage.
Fig.1.1.Illustrationsofavoltagedefinition
TheenergynecessarytomoveaunitpositivechargefrompointAtopointBis
proportionaltoΔV
AB=Uandcalledthevoltage.Certainlythenegativechargehas
oppositedirectiondefinedasacurrentflow.
If1J(joule)ofworkisrequiredtoreplace1Cofcharge,thevoltagebetween
twopointsisequalto1V(volt).
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