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CGS versus SI

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~~{{Warning|If hard core~~ The [https://en.wikipedia.org/wiki/International_System_of_Units SI or International System of Units] versus the [https://en.wikipedia.org/wiki/Centimetre%E2%80%93gram%E2%80%93second_system_of_units CGS or Centimetre–gram–second] system of units is a constant source of confusion in the field of NMR ~~or physics theory~~ . Both are based on the metric system, however the differences can result in quite different forms of the fundamental NMR equations. An example of this is Tesla versus Gauss units for the magnetic field strength. == CGS flavours == Note that in the CGS system, that there are different sets of units for electromagnetism. The major systems are [https://en.wikipedia.org/wiki/Centimetre_gram_second_system_of_units#Electrostatic_units_.28ESU.29 ESU], [https://en.wikipedia.org/wiki/Centimetre_gram_second_system_of_units#Electromagnetic_units_.28EMU.29 EMU], [https://en.wikipedia.org/wiki/Gaussian_units Gaussian units], and [https://en.wikipedia.org/wiki/Lorentz%E2%80%93Heaviside_units Lorentz-Heaviside units]. In NMR papers not ~~to your taste~~using SI units, ~~please do not read any further!}}~~the EMU system is most commonly used.

The [https://en.wikipedia.org/wiki/International_System_of_Units SI or International System of Units] versus the [https://en.wikipedia.org/wiki/Centimetre%E2%80%93gram%E2%80%93second_system_of_units CGS or Centimetre–gram–second] system of units is a constant source of confusion in the field of NMR. Both are based on the metric system, however the differences can result in quite different forms of the fundamental NMR equations. An example of this is Tesla versus Gauss units for the magnetic field strength.

== Units of measurement ==

! Symbol

! colspan="3" | SI unit

! colspan="3" | CGS unit(EMU)

! SI to CGS conversion factor

|-

! Name

! Symbol

! [https://en.wikipedia.org/wiki/SI_base_unit Base ~~unit~~units]

! Name

! Symbol

! Base ~~unit~~units

!

|-

|| ''L''

|style="text-align:left;"| metre

|| m

|style="text-align:left;"| centimetre

|| cm

|| 10−2

|| ''m''

|style="text-align:left;"| kilogram

|| kg

|style="text-align:left;"| gram

|| g

|| 10−3

|| ''t''

|style="text-align:left;"| second

|| s

|style="text-align:left;"| second

|| s

|| 1

! acceleration

|| ''a''

|style="text-align:left;"| [https://en.wikipedia.org/wiki/Metre_per_second_squared ~~Metre~~ metre per second squared]

||

|| m⋅s−2

|style="text-align:left;"| [https://en.wikipedia.org/wiki/Gal_%28unit%29 ~~Gal~~galileo]|| ~~gal~~Gal

|| cm⋅s−2

|| 10−2

|| kg⋅m2·s−3

|style="text-align:left;"| erg per second

|| ~~erg⋅s−1~~

|| g·cm2·s−3

|| 10−7

|-

! magnetic dipole moment|| ''μ''|style="text-align:left;"| Newton-meters per Tesla|||| A·m2|style="text-align:left;"| electromagnetic unit|| emu|| abA·cm2|| 10−3|-! magnetic flux density(B-field)

|| ''B''

|style="text-align:left;"| [https://en.wikipedia.org/wiki/Tesla_%28unit%29 Tesla]

|| kg·s−2·A−1

|style="text-align:left;"| [https://en.wikipedia.org/wiki/Gauss_%28unit%29 Gauss]

|| GGs|| ~~esu·cm~~Mx·cm−2

|| 10−4

|-

! magnetic flux density (H-field)

|| ''H''

|style="text-align:left;"| Amperes per metre

||

|| A·m−1

|style="text-align:left;"| [https://en.wikipedia.org/wiki/Oersted Oersted]

|| Oe

|| g·cm·s−2

|| 4π·10−3

|-

! magnetic flux

|| ''HΦB''

|style="text-align:left;"| [https://en.wikipedia.org/wiki/Weber_%28unit%29 Weber]

|| Wb

|| kg·m2·s−2·A−1

|style="text-align:left;"| [https://en.wikipedia.org/wiki/~~Oersted Oersted~~Maxwell_%28unit%29 Maxwell]|| OeMx|| ~~g·cm·s~~Mx|| 10−2−8|-! magnetic susceptibility|| ~~1000~~''χm''|style="text-align:left;"||| || -|style="text-align:left;"||| || -|| (4π)−1|-! electric current|| ''I''|style="text-align:left;"| [https://en.wikipedia.org/wiki/Ampere ampere]|| A|| A|style="text-align:left;"| [https://en.wikipedia.org/wiki/Abampere abampere] (or biot)|| abA (or Bi)|| abA (or Bi)|| 10−1|-! electric charge|| ''Q''|style="text-align:left;"| [https://en.wikipedia.org/wiki/Coulomb coulomb]|| C|| A·s|style="text-align:left;"| [https://en.wikipedia.org/wiki/Abcoulomb abcoulomb]|| abC|| abA·s|| 10−1|} == Constants == {|class="wikitable" style="text-align:center;"|-! Constant ! Symbol! colspan="3" | SI unit! colspan="3" | CGS unit (EMU)! SI to CGS conversion factor|-!!! Definition! Value! [https://en.wikipedia.org/wiki/SI_base_unit Base units]! Definition! Value! Base units!

|-

! magnetic force constant

|| ''k''A

|~~style="text-align:left;"~~| ~~Defined as~~ ''µ0''·(4π)−1|| || 10−7 || kg⋅m·s−2·A−3−2||Unity|| 1

||

~~|| 1~~

|| 4π·''µ0''−1

|-

! magnetic constant

|| ''µ0''

||||''µ0''|| 4π·10−7 || kg·m·s−2·A−3−2||||Unity

|| 1

||

|| ''µ0''−1

|}

== See also ==

[[Category:Theory]]

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