Editing Electric current (section)

== Conventions <span class="anchor" id="Current"></span> <!-- This section is linked from [[Hall effect]] and [[conventional current]] --> ==
[[Image:Current notation.svg|thumb|left|230px|The [[electron]]s, the [[charge carrier]]s in an electrical circuit, flow in the direction opposite that of the conventional electric current.]]
[[File:Battery symbol2.svg|thumb|right|100px|The [[electronic symbol|symbol]] for a battery in a [[circuit diagram]]]]

The conventional direction of current, also known as ''conventional current'',<ref name="Avison">{{cite book
 | last1  = Avison
 | first1 = John  
 | title  = The World of Physics
 | publisher = Thomas Nelson and Sons
 | date   = 2014
 | pages  = 221
 | url    = https://books.google.com/books?id=DojwZzKAvN8C&dq=%22conventional+current%22+positive+charge&pg=PA221
 | doi    = 
 | id     = 
 | isbn   = 9780174387336
 }}</ref><ref name="McComb">{{cite book
 | last1  = McComb
 | first1 = Gordon  
 | last2  = Boysen
 | first2 = Earl
 | title  = Electronics For Dummies
 | publisher = Wiley
 | date   = 2005
 | pages  = 12
 | url    = https://books.google.com/books?id=CvLkgK8PBJkC&dq=%22conventional+current%22&pg=PA12
 | doi    = 
 | id     = 
 | isbn   = 9780764597190
 }}</ref>  is arbitrarily defined as the direction in which {{em|positive}} charges flow. In a [[electrical conductor|conductive material]], the moving charged particles that constitute the electric current are called [[charge carrier]]s. In metals, which make up the wires and other conductors in most [[electrical circuit]]s, the positively charged [[atomic nucleus|atomic nuclei]] of the atoms are held in a fixed position, and the negatively charged [[electron]]s are the charge carriers, free to move about in the metal. In other materials, notably the [[semiconductor]]s, the charge carriers can be positive ''or'' negative, depending on the [[dopant]] used. Positive and negative charge carriers may even be present at the same time, as happens in an [[electrolyte]] in an [[electrochemical cell]].

A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention is needed for the direction of current that is independent of the type of [[charge carrier]]s. Negatively charged carriers, such as the electrons (the charge carriers in metal wires and many other electronic circuit components), therefore flow in the opposite direction of conventional current flow in an electrical circuit.<ref name="Avison" /><ref name="McComb" />

===Reference direction===
A current in a wire or [[circuit element]] can flow in either of two directions.  When defining a [[variable (mathematics)|variable]] <math>I</math> to represent the current, the direction representing positive current must be specified, usually by an arrow on the [[Circuit diagram|circuit]] [[schematic diagram]].<ref name="Kumar">{{cite book  
  | last = Kumar
  | first = K. S. Suresh
  | title = Electric Circuits & Networks
  | publisher = Pearson Education India
  | year = 2008
  | location =
  | pages = 26–28
  | url = https://books.google.com/books?id=ZzeXM-IQnIUC&pg=PA278
  | doi =
  | id =
  | isbn = 978-8131713907}}</ref><ref name="Hayt5">{{Cite book |last=Hayt |first= William |year= 1989 |title= Engineering Electromagnetics |edition= 5th |publisher= McGraw-Hill |isbn= 0070274061}}</ref>{{rp|13}}  This is called the ''reference direction'' of the current <math>I</math>.  When [[Circuit Analysis|analyzing electrical circuits]], the actual direction of current through a specific circuit element is usually unknown until the analysis is completed. Consequently, the reference directions of currents are often assigned arbitrarily. When the circuit is solved, a negative value for the current implies the actual direction of current through that circuit element is opposite that of the chosen reference direction.{{efn| Our first step in the analysis is the assumption of reference directions for the unknown currents.<ref name="Hayt5"></ref>}}{{rp|29}}