Editing Gauss (unit)

{{Short description|Unit of magnetic induction}}
{{Infobox unit
| name         = gauss
| image        = 
| caption      = 
| standard     = [[Gaussian units|Gaussian]] and [[Centimetre–gram–second_system_of_units#Electromagnetic_units_.28EMU.29|emu-cgs]]
| quantity     = [[magnetic flux]] density (also known as [[Magnetic_field#The_B-field|magnetic induction]], or the {{math|'''B'''}}-field, or magnetic field)
| symbol       = G ''or'' Gs
| symbol2      = 
| namedafter   = [[Carl Friedrich Gauss]]
| extralabel   = 
| extradata    = 
| units1       = [[SI derived units]]
| inunits1     = {{val|e=-4|u=tesla}}{{efn|The electromagnetic Gaussian and SI quantities ''correspond'' (symbol '≘') rather than being ''equal'' (symbol '{{=}}').}}
| units2       = Gaussian base units
| inunits2     = 1&nbsp;cm<sup>−1/2</sup>⋅<wbr/>g<sup>1/2</sup>⋅<wbr/>s<sup>−1</sup>
| units3       = [[Centimetre–gram–second system of units#Electrostatic units (ESU)|esu-cgs]]
| inunits3     = 1/{{math|''c''}}{{sub|cgs}}&nbsp;esu{{efn|{{math|''c''}}{{sub|cgs}} {{=}} {{val|2.99792458e10}} is the numeric part of the [[speed of light]] when expressed in cgs units.}}
}}
[[File:Bendixen_-_Carl_Friedrich_Gauß,_1828.jpg | thumb | right | Carl Friedrich Gauß in 1828, aged 50 years old]]
The '''gauss''' (symbol: '''{{val|u=G}}''', sometimes '''Gs''') is a unit of measurement of magnetic induction, also known as [[magnetic flux density]]. The unit is part of the [[Gaussian units|Gaussian system]] of units, which inherited it from the older [[centimetre–gram–second system of units#Electromagnetic units .28EMU.29|centimetre–gram–second electromagnetic units]] (CGS-EMU) system. It was named after the German mathematician and physicist [[Carl Friedrich Gauss]] in 1936. One gauss is defined as one [[maxwell (unit)|maxwell]] per square [[centimetre]].

As the [[centimetre–gram–second system of units]] (cgs system) has been superseded by the [[International System of Units]] (SI), the use of the gauss has been deprecated by the standards bodies, but is still regularly used in various subfields of science. The SI unit for magnetic flux density is the [[Tesla (unit)|tesla]] (symbol T),<ref>''NIST Special Publication 1038'', Section 4.3.1</ref> which corresponds to {{gaps|10,000|gauss}}.

==Name, symbol, and metric prefixes==
Although not a component of the International System of Units, the usage of the gauss generally follows the rules for SI units. Since the name is derived from a person's name, its symbol is the uppercase letter "G". When the unit is spelled out, it is written in lowercase ("gauss"), unless it begins a sentence.<ref name="SIBrochure9thEd">{{SIbrochure9th}}</ref>{{rp|147–148}}  The gauss may be combined with [[metric prefix]]es,<ref name="SIBrochure8th">{{SIbrochure8th}}</ref>{{rp|128}} such as in milligauss, mG (or mGs), or kilogauss, kG (or kGs).

==Unit conversions==
<math display="block">\begin{align}
1\,{\rm G} &= {\rm Mx}{\cdot}{\rm cm}^{-2} = \frac{\rm g}{{\rm Bi}{\cdot}{\rm s}^2}\\
           &\text{ ≘ } 10^{-4}\,{\rm T} = 10^{-4}\frac{\rm kg}{{\rm A}{\cdot}{\rm s^2}}
\end{align}</math>

The gauss is the unit of magnetic flux density '''B''' in the system of [[Gaussian units]] and is equal to [[Maxwell (unit)|Mx]]/cm<sup>2</sup> or [[gram (unit)|g]]/[[Abampere|Bi]]/s<sup>2</sup>, while the [[oersted]] is the unit of [[Magnetic_field#The_H-field|{{math|'''H'''}}-field]]. One [[tesla (unit)|tesla]] (T) corresponds to 10<sup>4</sup>&nbsp;gauss, and one [[ampere]] (A) per metre corresponds to 4π&nbsp;×&nbsp;10<sup>−3</sup> [[oersted]]. 
<!--
 A [[Abampere|biot]] (or [[abampere]]) is equal to 10 [[ampere]]s.<ref name="Hayt">Hayt, Jr., William H. (1974), ''Engineering Electromagnetics, Third Edition'', McGraw-Hill, {{ISBN|0-07-027390-1}}</ref><ref>Jackson, John (1975), ''Classical Electrodynamics, 2nd Ed.'', John Wiley, {{ISBN|0-471-43132-X}}</ref>
-->

The units for [[magnetic flux]]&nbsp;Φ, which is the [[integral]] of [[Magnetic_field#The_B-field|magnetic {{math|'''B'''}}-field]] over an [[area]], are the [[weber (unit)|weber]] (Wb) in the [[SI]] and the [[Maxwell (unit)|maxwell]] (Mx) in the CGS-Gaussian system. The conversion factor is {{val|e=8|u=maxwell per weber}}, since [[flux]] is the integral of field over an area, area having the units of the square of distance, thus {{val|e=4|u=G/T}} (magnetic field conversion factor) times the square of {{val|e=2|u=cm/m}} (linear distance conversion factor). 10<sup>8</sup>&nbsp;Mx/Wb = 10<sup>4</sup>&nbsp;G/T × (10<sup>2</sup>&nbsp;cm/m)<sup>2</sup>.

==Typical values==
{{main|Orders of magnitude (magnetic field)}}
* 10<sup>−9</sup>–10<sup>−8</sup> G – the magnetic field of the human brain
* 10<sup>−6</sup>–10<sup>−3</sup> G – the magnetic field of Galactic [[molecular clouds]]. Typical magnetic field strengths within the interstellar medium of the [[Milky Way]] are ~5 μG.
* 0.25–0.60 G – the [[Earth's magnetic field]] at its surface
* 4 G – near [[Jupiter]]'s equator
* 25 G – the Earth's magnetic field in its [[Earth's outer core|core]]<ref name="buff2010">Buffett, Bruce A. (2010), "Tidal dissipation and the strength of the Earth's internal magnetic field", ''Nature'', volume 468, pages 952–954, {{doi|10.1038/nature09643}}</ref>
* 50 G – a typical [[refrigerator magnet]]
* 100 G – an [[iron]] [[magnet]]
* 1500 G – within a [[sun spot]]<ref>{{Cite web |url=http://www.coolmagnetman.com/magflux.htm |title=How strong are magnets?|last=Hoadley |first=Rick |website=www.coolmagnetman.com |access-date=2017-01-26 }}</ref>
* 10000 to 13000 G – [[remanence]] of a [[neodymium magnet|neodymium-iron-boron (NIB) magnet]]<ref>{{cite book |url=https://books.google.com/books?id=_y3LSh1XTJYC&pg=PT232 |page=232 |title=Design of Rotating Electrical Machines |first1=Juha |last1=Pyrhönen |first2=Tapani |last2=Jokinen |first3=Valéria |last3=Hrabovcová |publisher=John Wiley and Sons |year=2009 |isbn=978-0-470-69516-6 }}</ref>
* 16000 to 22000 G – [[saturation (magnetic)|saturation]] of high permeability iron alloys used in transformers<ref>{{cite book |editor1-last=Laughton |editor1-first=Michael A. |editor2-last=Warne |editor2-first=Douglas F. |title=Electrical Engineer's Reference Book |edition=Sixteenth |publisher=Newnes |year=2003 |isbn=0-7506-4637-3 |chapter=8 }}</ref>
* 3000–70000 G – a medical [[magnetic resonance imaging|magnetic resonance imaging machine]] 
* 10<sup>12</sup>–10<sup>13</sup> G – the surface of a [[neutron star]]<ref>{{cite web |title=How strong are magnets? |work=Experiments with magnets and our surroundings |publisher=Magcraft |url=http://www.coolmagnetman.com/magflux.htm |access-date=2007-12-14 }}</ref>
* 4 × 10<sup>13</sup> G – the [[Schwinger limit]]
* 10<sup>14</sup> G – the magnetic field of [[SGR J1745-2900]], orbiting the supermassive black hole [[Sagittarius A*|Sgr A*]] in the center of the Milky Way.
* 10<sup>15</sup> G – the magnetic field of some newly created [[magnetar]]s<ref name="sciam_article">{{cite web 
 |date        = March 2003
 |first       = Robert C. 
 |last        = Duncan
 |url         = http://solomon.as.utexas.edu/~duncan/magnetar.html#Epilog
 |title       = Magnetars, Soft Gamma Repeaters and Very Strong Magnetic Fields
 |publisher   = University of Texas at Austin
 |access-date  = 2007-05-23
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20070611144512/http://solomon.as.utexas.edu/~duncan/magnetar.html#Epilog
 |archive-date = 2007-06-11
}}</ref>
* 10<sup>17</sup> G – the upper limit to neutron star magnetism<ref name="sciam_article" />

==See also==
*[[Tesla (unit)]]
*[[Centimetre–gram–second system of units]]
*[[Gaussian units]]

== Notes ==
{{notelist}}

==References==
{{reflist}}

{{CGS units}}

[[Category:Centimetre–gram–second system of units]]
[[Category:Units of magnetic flux density]]
[[Category:Carl Friedrich Gauss|Unit]]