Editing Electricity (section)

===Electric current===
{{Main|Electric current}}

The movement of electric charge is known as an [[electric current]], the intensity of which is usually measured in [[ampere]]s. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current. Electric current can flow through some things, [[electrical conductor]]s, but will not flow through an [[electrical insulator]].<ref>{{citation|last=Al-Khalili|first=Jim|title=Shock and Awe: The Story of Electricity|work=BBC Horizon}}</ref>

By historical convention, a positive current is defined as having the same direction of flow as any positive charge it contains, or to flow from the most positive part of a circuit to the most negative part. Current defined in this manner is called [[conventional current]]. The motion of negatively charged electrons around an [[electric circuit]], one of the most familiar forms of current, is thus deemed positive in the ''opposite'' direction to that of the electrons.<ref>
{{Citation
| first = Robert | last = Ward
| title = Introduction to Electrical Engineering
| publisher = Prentice-Hall
| page = 18
| year = 1960}}
</ref> However, depending on the conditions, an electric current can consist of a flow of [[charged particle]]s in either direction or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation.

[[File:Lichtbogen 3000 Volt.jpg|thumb|left|alt=Two metal wires form an inverted V shape. A blindingly bright orange-white electric arc flows between their tips.|An [[electric arc]] provides an energetic demonstration of electric current.]]

The process by which electric current passes through a material is termed [[electrical conduction]], and its nature varies with that of the charged particles and the material through which they are travelling. Examples of electric currents include metallic conduction, where electrons flow through a [[Electrical conductor|conductor]] such as metal, and [[electrolysis]], where [[ion]]s (charged [[atom]]s) flow through liquids, or through [[plasma (physics)|plasmas]] such as electrical sparks. While the particles themselves can move quite slowly, sometimes with an average [[drift velocity]] only fractions of a millimetre per second,<ref name=Duffin/>{{rp|17}} the [[electric field]] that drives them itself propagates at close to the [[speed of light]], enabling electrical signals to pass rapidly along wires.<ref>
{{Citation
| first = L.
| last = Solymar
| title = Lectures on electromagnetic theory
| publisher = Oxford University Press
| page = [https://archive.org/details/lecturesonelectr0000soly_w5c6/page/140 140]
| year = 1984
| isbn = 0-19-856169-5
| url = https://archive.org/details/lecturesonelectr0000soly_w5c6/page/140
}}
</ref>

Current causes several observable effects, which historically were the means of recognising its presence. That water could be decomposed by the current from a voltaic pile was discovered by [[William Nicholson (chemist)|Nicholson]] and [[Anthony Carlisle|Carlisle]] in 1800, a process now known as [[electrolysis]]. Their work was greatly expanded upon by [[Michael Faraday]] in 1833. Current through a [[electrical resistance|resistance]] causes localised heating, an effect [[James Prescott Joule]] studied mathematically in 1840.<ref name=Duffin/>{{rp|23–24}} One of the most important discoveries relating to current was made accidentally by [[Hans Christian Ørsted]] in 1820, when, while preparing a lecture, he witnessed the current in a wire disturbing the needle of a magnetic compass.<ref name=berkson>
{{Citation
| first = William
| last = Berkson
| title = Fields of Force: The Development of a World View from Faraday to Einstein
| publisher = Routledge
| year = 1974
| isbn = 0-7100-7626-6
| url = https://archive.org/details/fieldsofforcedev0000berk/page/370
}}</ref>{{rp|p=370}}{{efn|Accounts differ as to whether this was before, during, or after a lecture.}} He had discovered [[electromagnetism]], a fundamental interaction between electricity and magnetics. The level of electromagnetic emissions generated by [[electric arc]]ing is high enough to produce [[electromagnetic interference]], which can be detrimental to the workings of adjacent equipment.<ref>{{cite web | title = Lab Note #105 ''EMI Reduction – Unsuppressed vs. Suppressed'' | publisher = Arc Suppression Technologies | date = April 2011 | url = http://www.arcsuppressiontechnologies.com/arc-suppression-facts/lab-app-notes/ | access-date = March 7, 2012 | archive-date = March 5, 2016 | archive-url = https://web.archive.org/web/20160305123758/http://www.arcsuppressiontechnologies.com/arc-suppression-facts/lab-app-notes/ | url-status = live}}</ref>

In engineering or household applications, current is often described as being either [[direct current]] (DC) or [[alternating current]] (AC). These terms refer to how the current varies in time. Direct current, as produced by example from a [[Battery (electricity)|battery]] and required by most [[Electronics|electronic]] devices, is a unidirectional flow from the positive part of a circuit to the negative.<ref name=bird>
{{citation
| first = John | last = Bird
| title = Electrical and Electronic Principles and Technology, 3rd edition
| publisher = Newnes
| year = 2007
| isbn =978-1-4175-0543-2}}
</ref>{{rp|11}} If, as is most common, this flow is carried by electrons, they will be travelling in the opposite direction. Alternating current is any current that reverses direction repeatedly; almost always this takes the form of a [[sine wave]].<ref name=bird/>{{rp|206–07}} Alternating current thus pulses back and forth within a conductor without the charge moving any net distance over time. The time-averaged value of an alternating current is zero, but it delivers energy in first one direction, and then the reverse. Alternating current is affected by electrical properties that are not observed under [[steady state]] direct current, such as [[inductance]] and [[capacitance]].<ref name=bird/>{{rp|223–25}} These properties however can become important when circuitry is subjected to [[transient response|transients]], such as when first energised.