# 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 forcedyn 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