Difference between revisions of "Emu system"
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| − | The '''emu system''' was a system of units for measuring electrical and magnetic quantities based on the [[CGS system|centimetre–gram–second (CGS) system]]. They were developed by the [[British Association for the Advancement of Science]] (B.A.) from 1862 to 1873, based on an original idea by [[Wilhelm Weber|Weber]], and rendered obsolete by the introduction of electrical and magnetic units into the [[International System of Units]] (SI) in 1948. | + | The '''emu system''' was a system of units for measuring electrical and magnetic quantities based on the [[CGS system|centimetre–gram–second (CGS) system]]. They were developed by the [[British Association for the Advancement of Science]] (B.A.) from 1862 to 1873,<ref>{{citation | first = Fleeming | last = Jenkin | authorlink = Fleeming Jenkin | title = Reports of the Committee on Electrical Standards | location = London | year = 1873}}.</ref><ref name="EB11">{{citation | contribution = Units, Physical | title = Encyclopædia Britannica | volume = 27 | year = 1911 | edition = 11th | pages = 738–45}}.</ref> based on an original idea by [[Wilhelm Weber|Weber]],<ref group="Note">Weber's original proposal was based on a millimetre–milligram–second system of units.</ref> and rendered obsolete by the introduction of electrical and magnetic units into the [[International System of Units]] (SI) in 1948.<ref>{{SIbrochure8th|page=144}}.</ref> |
| − | The emu system was usually treated as a non-rationalized three-quantity system in which [[electric current]], for example, had the [[dimension]] | + | The emu system was usually treated as a non-rationalized three-quantity system in which [[electric current]], for example, had the [[dimension]] [[force]]<sup>½</sup>. The [[magnetic constant]] (known at the time as the "permeability of free space") was literally ignored: in modern terms, it was set as dimensionless and with a value of 1. For these reasons, the form of [[quantity equation]]s intended for use with the emu system is often different from that of the corresponding equations in the four-quantity rationalized [[International System of Quantities]].<ref>{{GreenBook2nd|pages=117–23}}.</ref> |
==Units== | ==Units== | ||
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|- | |- | ||
| emu of [[electric current]] | | emu of [[electric current]] | ||
| − | | abampere<br/>biot | + | | [[abampere]]<br/>[[biot]] |
| 10 [[Ampere|A]] | | 10 [[Ampere|A]] | ||
| + | |- | ||
| + | | emu of [[electric charge]] | ||
| + | | [[abcoulomb]] | ||
| + | | 10 [[Coulomb|C]] | ||
| + | |- | ||
| + | | emu of [[capacitance]] | ||
| + | | [[abfarad]] | ||
| + | | 10<sup>9</sup> [[Farad|F]] | ||
| + | |- | ||
| + | | emu of [[inductance]] | ||
| + | | [[abhenry]] | ||
| + | | 10<sup>−9</sup> [[Henry|H]] | ||
| + | |- | ||
| + | | emu of [[electric conductance]] | ||
| + | | [[abmho]] | ||
| + | | 10<sup>9</sup> [[Siemens|S]] | ||
| + | |- | ||
| + | | emu of [[electric resistance]] | ||
| + | | [[abohm]] | ||
| + | | 10<sup>−9</sup> [[Ohm|Ω]] | ||
| + | |- | ||
| + | | emu of [[electromotive force]] | ||
| + | | [[abvolt]] | ||
| + | | 10<sup>−8</sup> [[Volt|V]] | ||
|- | |- | ||
|} | |} | ||
Revision as of 04:57, 12 August 2010
The emu system was a system of units for measuring electrical and magnetic quantities based on the centimetre–gram–second (CGS) system. They were developed by the British Association for the Advancement of Science (B.A.) from 1862 to 1873,[1][2] based on an original idea by Weber,[Note 1] and rendered obsolete by the introduction of electrical and magnetic units into the International System of Units (SI) in 1948.[3]
The emu system was usually treated as a non-rationalized three-quantity system in which electric current, for example, had the dimension force½. The magnetic constant (known at the time as the "permeability of free space") was literally ignored: in modern terms, it was set as dimensionless and with a value of 1. For these reasons, the form of quantity equations intended for use with the emu system is often different from that of the corresponding equations in the four-quantity rationalized International System of Quantities.[4]
Units
| Name | SI equivalent | |
|---|---|---|
| emu of electric current | abampere biot |
10 A |
| emu of electric charge | abcoulomb | 10 C |
| emu of capacitance | abfarad | 109 F |
| emu of inductance | abhenry | 10−9 H |
| emu of electric conductance | abmho | 109 S |
| emu of electric resistance | abohm | 10−9 Ω |
| emu of electromotive force | abvolt | 10−8 V |
Notes and references
Notes
- ↑ Weber's original proposal was based on a millimetre–milligram–second system of units.
References
- ↑ Jenkin, Fleeming Reports of the Committee on Electrical Standards; London, 1873.
- ↑ Units, Physical. In Encyclopædia Britannica, 11th ed., 1911; Vol. 27, pp 738–45.
- ↑ The International System of Units (SI), 8th ed.; International Bureau of Weights and Measures: Sèvres, France, 2006; p 144. ISBN 92-822-2213-6, <http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf>.
- ↑ Quantities, Units and Symbols in Physical Chemistry, 2nd ed.; Blackwell Science: Oxford, 1993; pp 117–23. ISBN 0-63203-5838, <http://old.iupac.org/publications/books/gbook/green_book_2ed.pdf>.
External links
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