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== Electricity and the natural world ==
=== Physiological effects ===
{{main|Electric shock}}
A voltage applied to a human body causes an electric current through the tissues, and although the relationship is non-linear, the greater the voltage, the greater the current.<ref name=tleis>
{{Citation
| first = Nasser | last = Tleis
| title = Power System Modelling and Fault Analysis
| publisher = Elsevier
| year = 2008
| pages = 552–554
| isbn = 978-0-7506-8074-5}}
</ref> The threshold for perception varies with the supply frequency and with the path of the current, but is about 1&nbsp;mA for mains-frequency electricity.<ref>
{{Citation
| first = Sverre | last = Grimnes
| title = Bioimpedance and Bioelectricity Basic
| publisher = Academic Press
| year = 2000
| pages = 301–309
| isbn = 0-1230-3260-1}}
</ref> If the current is sufficiently high, it will cause muscle contraction, [[fibrillation]] of the heart, and [[burn|tissue burns]].<ref name=tleis/> The lack of any visible sign that a conductor is electrified makes electricity a particular hazard. The pain caused by an electric shock can be intense, leading electricity at times to be employed as a method of [[torture]]. Death caused by an electric shock is referred to as [[electrocution]]. Electrocution is still the means of [[capital punishment|judicial execution]] in some jurisdictions, though its use has become rarer in recent times.<ref>
{{Citation
| first = J.H. | last = Lipschultz
| first2 = M.L.J.H. | last2 = Hilt
| title = Crime and Local Television News
| publisher = Lawrence Erlbaum Associates
| year = 2002
| page = 95
| isbn = 0805836209}}
</ref>
 
=== Electrical phenomena in nature ===
[[किपा:Electric-eel2.jpg|thumb|right|The electric eel, ''Electrophorus electricus'']]
Electricity is by no means a purely human invention, and may be observed in several forms in nature, a prominent manifestation of which is [[lightning]]. The [[Earth's magnetic field]] is thought to arise from a [[dynamo theory|natural dynamo]] of circulating currents in the planet's core.<ref>
{{citation
|first=Thérèse |last=Encrenaz
|title=The Solar System
|page=217
|publisher=Springer
|isbn=3540002413}}
</ref> Certain crystals, such as [[quartz]], or even [[sugarcane]], generate a potential difference across their faces when subjected to external pressure.<ref name=crystallography>
{{citation
|first=José |last=Lima-de-Faria
|first2=Martin J. last2= Buerger
|title=Historical Atlas of Crystallography
|page=67
|publisher=Springer
|isbn=079230649X}}
</ref> This phenomenon is known as [[piezoelectricity]], from the [[Greek language|Greek]] ''piezein'' (πιέζειν), meaning to press, and was discovered in 1880 by [[Pierre Curie|Pierre]] and [[Jacques Curie]]. The effect is reciprocal, and when a piezoelectric material is subjected to an electric field, a small change in physical dimensions take place.<ref name=crystallography/>
 
Some organisms, such as [[shark]]s, are able to detect and respond to changes in electric fields, an ability known as [[electroreception]],<ref name=Biodynamics>
{{citation
| first = Vladimir & Tijana | last = Ivancevic
| title = Natural Biodynamics
| page = 602
| publisher = World Scientific
| year = 2005
| isbn = 9812565345}}
</ref> while others, termed [[electrogenic]], are able to generate voltages themselves to serve as a predatory or defensive weapon.<ref name=Electroreception/> The order [[Gymnotiformes]], of which the best known example is the [[electric eel]], detect or stun their prey via high voltages generated from modified muscle cells called [[electrocytes]].<ref name=morris/><ref name=Electroreception/> All animals transmit information along their cell membranes with voltage pulses called [[action potential]]s, whose functions include communication by the nervous system between neurons and muscles.<ref name="neural science">
{{citation
| first = E. | last = Kandel
| first2 = J. last2 = Schwartz
| first3 = T. | last3 = Jessell
| title = Principles of Neural Science
| pages = 27–28
| year = 2000
| publisher = McGraw-Hill Professional
| isbn = 0838577016}}
</ref> (Because of this principle, an electric shock can induce temporary or permanent [[paralysis]] by "overloading" the nervous system.) They are also responsible for coordinating activities in certain plants.<ref name="neural science"/>
 
== See also ==
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