Oersted (unit)

Physical unit
Unit name	Oersted
Unit symbol	${\displaystyle \mathrm {Oe} }$
Physical quantity (s)	Magnetic field strength
dimension	${\displaystyle {\mathsf {M^{1/2}L^{-1/2}T^{-1}}}}$
system	Electromagnetic CGS unit system , Gaussian CGS unit system
In SI units	${\displaystyle \mathrm {1\,Oe\;{\mathrel {\hat {=}}}\;79{,}5775\;{\frac {A}{m}}} }$
In CGS units	${\displaystyle \mathrm {1\,Oe=1\;{\frac {\sqrt {g}}{{\sqrt {cm}}\cdot {s}}}} }$
Named after	Hans Christian Ørsted

Oersted (unit symbol  Oe ; after the Danish physicist Hans Christian Ørsted ) is the unit of magnetic field strength in the Gaussian and electromagnetic CGS system of units . It has not been an official unit since 1970 .

An oersted was defined as the magnetic field strength at which the force 1  dyn acts on a unit pole .

Full definition

In magnetostatics, a unit pole is the analogue of the electric charge in electrostatics. In a magnetostatic quantity system, "Coulomb's law for magnetic poles" applies

${\displaystyle F={\frac {p\,p}{r^{2}}}}$.

Two uniform poles of the same kind have a pole strength if they repel each other with a force at a distance in a vacuum . At one point of a magnetic field has the field strength ${\displaystyle p=1\,\mathrm {cm} {\sqrt {\mathrm {dyn} }}}$ ${\displaystyle r=1\,\mathrm {cm} }$ ${\displaystyle F=1\,\mathrm {dyn} }$

${\displaystyle {\vec {H}}=\lim _{p\to 0}{\frac {\vec {F}}{p}}}$

the value of one oersted when a unit pole experiences a force from one dyn.

conversion

The unit Oersted has no equivalent in the SI system of units , because the magnetic field strength in the associated international size system has a different dimension . A field strength in Oersted corresponds to a field strength in amperes per meter of:

${\displaystyle 1\,\mathrm {Oe} \ {\mathrel {\hat {=}}}\ {\frac {1000}{4\pi }}\,{\frac {\mathrm {A} }{\mathrm {m} }}\approx 79{,}5775\,{\frac {\mathrm {A} }{\mathrm {m} }}}$

By multiplying by the magnetic field constant , a magnetic flux density of 1  Gs in the Gaussian CGS system of units or of 100  µ T in the SI system of units is obtained in a vacuum (where, since the new definition of the SI units in 2019, the relationship μ ₀  = 4π · 10 ^{- 7}  Vs / Am only approximately applies): ${\displaystyle \mu _{0}}$

${\displaystyle \mu _{0}\cdot 1\,\mathrm {Oe} =1\,\mathrm {Gs} \ {\mathrel {\hat {=}}}\ 4\pi \cdot 10^{-7}{\frac {\mathrm {Vs} }{\mathrm {Am} }}\cdot {\frac {1000}{4\pi }}\,{\frac {\mathrm {A} }{\mathrm {m} }}=10^{-4}\,\mathrm {T} =100\,\mu \mathrm {T} }$

The energy product of permanent magnets is often given in M G · Oe.

literature

• L. Ruppert: History of the International Electrotechnical Commission . Buereau Central de la Commission Electrotechnique Internationale, Geneva 1956 ( Online (PDF; 977 kB)).

Individual evidence

1. ↑ Ludwig Bergmann, Clemens Schaefer: Electricity . Walter de Gruyter, 1966, ISBN 978-3-11-144188-7 , p. 175.
2. ^ Wilhelm H. Westphal: Physics: A textbook . Springer-Verlag, 2013, ISBN 3-662-30391-4 , pp. 364 ( limited preview in Google Book search).
3. ↑ Ludwig Bergmann, Clemens Schaefer: Electricity . Walter de Gruyter, 2013, ISBN 3111441873 , p. 95.
4. ^ Müller / Krauss, Handbuch für die Schiffsführung, 8th edition from 1983, ISBN 3-540-12100-5 , p. 67