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Oersted
The Danish physicist Hans Christian Oersted recognized in 1820 the magnetic effect of electric current. According to him, therefore, a special unit has been named: The unit Oersted is used for the measurement of magnetic fields (unit H). The abbreviation of Oersted is Oe.
Historical background
The discovery of the Copenhagen scientist clarified the effect of an electric current on a magnetic field. He thus made a major contribution to the study of magnetism - but he was not the first physicist who made a connection between electricity and magnetism. However, the earlier discoveries of other physicists had been forgotten.
Even today, magnetic and electrical forces are confused. Hans Christian Oersted first recognized the significance of the connection between these two forces for modern and electro technical applications. However, the relationship between magnetism and electricity was not fully described until 1864 by Maxwell with the well-known Maxwell equations. These equations still form the cornerstone of electrodynamics today.
Oersted's attempt
Until Oersted's groundbreaking discovery, magnetism and electricity were barely associated. If you look at the very simple attempt by Oersted, it becomes clear why he is also called the father of electrical engineering.
A compass needle is mounted parallel to a conductor wire. In a natural state, it aligns itself in the usual way according to the earth's magnetic field, i.e. to the magnetic north pole. When the power source is turned on and the power is successively increased, the compass needle moves and is finally level with the conductor, which means, no longer in north-south, but in east-west direction. If the current is taken away again, the compass needle expires in its original starting position.
From this, Oersted was able to deduce that the electric current exerts a magnetic effect on the compass needle, i.e. the conductor is surrounded by a kind of field: the magnetic field. The stronger the current flow, the stronger this magnetic field. The direction of the current flow also plays a role. When reversing the experiment, the compass needle moves in the opposite direction. Thus, the magnetic field can take another direction.
The unit Oersted and their derivation in physics
The actually better known unit Tesla does not serve - as often erroneously assumed - the measurement of a magnetic field, but the magnetic flux density (unit B). In a vacuum, a magnetic flux density of one Tesla corresponds to a magnetic field of 10,000 Oersteds. Thus, a magnetic field from an oersted would be pretty weak.
As a measure or unit for the magnetic field strength Oersted is defined in the cgs system. This system consists of the physical base unit’s gram (g), centimeter (cm), second (s), candela, mol, and kelvin (K) and ampere (A). This system is rarely used today:
The reason is the generally accepted SI system. In this, the base unit is not grams and centimeters but kilograms (kg) and meters (m). The magnetic field strength is measured in the SI system not with Oersted, but in A / m. Unfortunately; an oersted in the SI system cannot be converted smoothly. By definition, a magnetic flux density of 0.1 mT corresponds to a magnetic field of one oersted (in vacuum).
The unit Tesla, however, is a SI unit. It is used to give the magnetic field H, which is calculated from the magnetic flux density B and the magnetic permeability in vacuum:
measure A / m comes about through this permeability constant:
An oersted is therefore 79.577 A / m or
In literature, sometimes the unit Tesla is the measure of the strength of a magnetic field. However, this is not true, since Tesla or Gauss describe the magnetic flux density. The magnetic field is given by the unit Oersted, or amperes per meter.