Magnetism

of these articles describes at present (by forwarding) also the terms magnetic field, magnetization. Supplementing information is in the article magnet. Electromagnetism is discussed also in the article electrodynamics.

Magnetism is a physical phenomenon, itself as Kraftwirkung between Magnets, magnetized and/or. magnetizable articles and electrical charges moved such as z. B. in stromdurchflossenen leaders expresses. The switching these Kraft is made by a magnetic field, which is produced on the one hand by these objects and on the other hand it affects. All manifestations ofMagnetism can be led back in the long run on the movement of electrical charges or the magnetic moment of elementary particles as consequence of their spin. The magnetism is a subsection of the electromagnetism, which one of the four basic forces of physics represents.

Table of contents

magnetic fields

magnetic fields belonging to the category of the fields.

Lines of flux

magnetic lines of flux in the environment of a bar magnet, visibly made with iron filings on paper

magnetic lines of flux give the direction of the magnetic field in each pointand/or. the magnetic river on. The distance between neighbouring lines of flux is a reference point for the strength of the magnetic field: the more closely the lines of flux, the more strongly the field.

Magnetic lines of flux do not have a beginning and no end, but run as closed courses. Inthe Magnetostatik there are no charges contrary to electrostatics - magnetic monopolies are mathematically conceivable, all experimental facts speak however against their existence. Thus the magnetic field is pour-free.

Magnetic lines of flux can by the adjustment of iron filings visiblyare made; for three-dimensional demonstrations one can suspend the iron filings for example in silicone oil.

Magnetic Kraftwirkung

the magnetic field exercises a Kraft on moved charges, the so-called Lorentzkraft. It works perpendicularly to the lines of flux of the magnetic field as well asperpendicularly to the direction of motion of the charge.

Furthermore the magnetic field exerts forces on magnets and magnetizable bodies. In the simplest case one can describe these sample test specimens as magnetic dipoles. The magnetic field exercises a torque on the sample test specimen and arranges it tangential to the lines of flux out. This effect is used for example with the magnetic compass, in which the compass needle, a magnetic dipole, aligns itself after the earth's magnetic field.

During the reciprocal effect between two such dipoles, the two arrange themselves for example two bar magnetsMagnets by this torque first parallel out. Since ungleichnamige poles dress and repel of the same name, the two magnets turn thereby ungleichnamige poles each other. In this arrangement the two magnets dress. A cause is that the attraction on thatturned pole a magnet is larger than the repulsion on his turned away, since the magnetic field of the other magnet with the distance decreases. In the mathematical description Kraft therefore the gradient of the magnetic field plays a role.

The forces betweentwo magnets can be explained also over the view of the energy, which represents the magnetic field. Afterwards the forces work always in such a way that the total energy of the field decreases, if the magnets would follow them.

Sizes and units

the strength of a magnetic fieldthe magnetic field strength H by two different physical dimension, ( unit can be expressed: A/m) and the magnetic flow density B (unit Tesla). While the magnetic field strength is of advantage with computations with electric currents, one uses the magnetic flow density toCompute from induced tensions or the Lorentzkraft. The two field sizes are over a material-dependent conversion factor are linked with one another, the permeability called.

At present one finds strongest

and weakest magnetic field the magnetic field of the earth weakest with 0,000000001 Tesla (1 NT) ina particularly shielded cubic building of the Federal Standards Laboratory in Berlin. Purpose of the Kubus is the measurement of the weak brain stream of humans.

At national the High Magnetic Field Laboratory ([1]) in Tallahassee (Florida) becomes with 45 the Tesla at presentstrongest (sturdy) magnetic field of the earth produces. By means of intensive laser radiation even magnetic fields of up to 34.000 Tesla can be produced - however only for the extremely short time interval of approximately 10 picoseconds.

On the surface of neutron stars, like z.B.To pulse arene, against it typically flow densities of the magnetic fields of 10 8 Tesla , with magnet arene , to a special sort of neutron stars, prevail even 10 11 Tesla.

Electromagnetism

magnetic fields are produced by the movement of electrical charges. The speed (in amount and), As well as the size of (amount and sign) of the moved charges the strength and direction of the magnetic forces determine direction. For a abstraktere representation of electromagnetism see the article electrodynamics.

Ein Strom I, der durch einen geradlinigen Leiter fließt, erzeugt ein Magnetfeld B, dessen Feldlinien kreisförmig um den Leiter herum verlaufen. Man kann sich dies mit der Rechte-Faust-Regel merken: der Daumen zeigt in Richtung von I, die übrigen Finger deuten ringförmige Magnetfeldlinien an.
A river I, which flows by a straight-line leader, producesa magnetic field B, whose lines of flux run in a circle around the leader. One can note this with the right rule of thumb: the thumb shows the remaining fingers toward of I, suggests circular Magnetfeldlinien.

A constant movement of charge carrierscauses a magnetic field, which follows the following regulating:

  • For an electric current, which flows by a wire, the direction of the magnetic field can be intended with the help of the being right lp rule: The leader is covered in such a way that the spread thumb the conventional/technical direction of current(against the electron flow) indicates, then the fingers indicate the direction of the developing magnetic field.
  • To a circle stream applies: If the fingers of the right hand are curved toward the electron flow, the thumb shows toward the magnetic north pole.
  • AnotherRule for this is the right screw rule in such a way specified.
  • Measurement of magnetic fields is among other things with Hallsonden possible.

In electrical conductors, that move by a magnetic field, a tension and a current flow are induced if necessary.

Temporally variable movement ofResults to charge carriers in a differenzialen change in the electrostatic and magnetic field of its environment. One speaks the frequency of the change of electromagnetic waves if in given media spreads. Light (all the same whether visibly or invisibly) and broadcast are the most well-known formsthis Prinzipes. In addition, in metalworking (induction furnaces) and to heating up even non conductive substances this form of electromagnetism is used (microwave oven).

Magnetism of the subject

magnetic moment many elementary particles

loaded by elementary particle possess a characteristic magnetic moment <math> \ vec {\ mu}< /math>. It is linked with their spin, which one can interpret in the context of a conceivable picture as rotation of the particles around itself.


Magnetic moment <math> \ mu< /math> some elementary particles
elementary particle designation < math> \ mu/(\ rm {JT^ {- 1}})< /math>
Electron <math> \ mu_ {\ rm e}< /math> <math> -9 {,} 284.764.12 (80) \ cdot10^ {- 24}< /math>
Myon <math> \ mu_ {\ rm \ mu}< /math> <math> -4 {,} 490.447.99 (40) \ 10^ cdot {- 26}< /math>
Proton <math> \ mu_ {\ rm p}< /math> <math> 1 {,} 410.606.71 (12) \ cdot 10^ {- 26}< /math>
Neutron <math> \ mu_ {\ rm N}< /math> <math> -0 {,} 966.236.45 (24) \ 10^ cdot {- 26}< /math>

Magnetic moment of atoms

the magnetic moment of an atom sits down together from the contribution of the electron sheath (covering moment), and to thatgenerally much weaker core contribution (core moment).

To the covering moment, carries that orbital moment, which is linked with the angular momentum of the electrons, and which determined spin moment by the electron spin. The sum of the magnetic moments of the electrons of a fully filled (Sub) bowl results in in each casezero, so that atoms, which do not possess part-filled bowls, do not exhibit a permanent covering moment. In the outside magnetic field however a magnetic moment is induced, which works against its emergence (repulsive Kraft in the inhomogenous magnetic field). One calls atoms with this characteristic dia.-magnetically. Atoms alsopart-filled bowls exhibit however a permanent covering moment. Such atoms are called paramagnetic. Even if the core moment is very small, it does not only let prove (NMR, “Nuclear Magnetic Resonance” = core-magnetic resonance), but also practically uses itself (e.g. Kernspintomografie).

Magnetism of solids

the magnetism of solids has generally its origin in the magnetism of the atoms/ions and electrons (spin), of which the solid body is composed. Strictly speaking one speaks only then of onemagnetic material, if the elementary (microscopic) magnetic moments are so aligned that they do not compensate themselves at least completely mutually, the material thus a macroscopic magnetization exhibit. Well-known examples are the ferrousmagnetic metals nickel and cobalt or also the mineral magnetite. In addition, if a material does not exhibit macroscopic magnetization, it can be affected by magnetic fields; such effects are usually however much too weak, in order to be able to observe it in the everyday life. The Magnetochemie, a subrange that Physical chemistry examines the magnetic characteristics of substances.

With the magnetism of solids it concerns a cooperative phenomenon. Even if the components (atoms, ions, quasi-free electrons), from which the solid body is developed, nonvanishing magneticMoments carry, exhibit only few materials a macroscopic magnetization . Usually the elementary magnetic moments are in such a way aligned that they compensate themselves mutually. The reason for it is that the bonding electrons, which determine the magnetic characteristics of the atoms,contribute now to the chemical connection. With the distribution of the electrons on the new connection conditions the mutual orientation of the electrons is determined by the exchange reciprocal effect. This is usually unfavorable for a parallel adjustment of the magnetic moments energetically. An exceptionof it e.g. place. the transition metals iron, nickel and cobalt . One calls such materials ferrousmagnetically (of lat. ferrum, iron). Starting from a certain temperature, the so-called. Curie temperature (after Pierre curie and Marie curie, Nobelpreis physics 1903), outweighsthe thermal energy the energy of the exchange reciprocal effect, and the ferrousmagnetic order is broken open. The solid body changes then into the paramagnetic phase. Whether an element and/or. a solid body is ferrousmagnetic by the Stoner criterion is determined: Is the product outExchange constant and density of states at the Fermikante more largely than one, then are present ferromagnetism . To domains in the ferrous magnet see also ferromagnetism.

The ferrousmagnetic order is a special case of the magnetic order. Apart from the unordered condition there are still different formsthe magnetic order, among them antiferromagnetism and spin density waves.

A diagram of the exchange integral is given by the Bethe Slater curve. In this diagram one can recognize, which materials ferrousmagnetically, antiferromagnetically or paramagnetic are.

Magnetism in biology

magnetic alternating fields know over Induction electric currents in the fabric release and can so (weak) an influence on the nervous system have. For example so-called Magnetophosphene is, meant is optical sensory perceptions to observe with appropriate fields. Also the motor Cortex (grosshirn) can so alsoAssistance of the Transkraniellen Magnetstimulation (TMS) to be stimulated that it comes to automatic muscle contractions. The moreover it is for a long time well-known that magnetic alternating fields can affect the secretion of hormones (example Melatonin).

Birds can orient themselves by means of the earth's magnetic field.

The physician Franz Anton Mesmer developed a theory, which was examined and rejected 1784 by the French Academy of Sciences, after the one fluid, which called Mesmer magnetism animalis, from humans to humans is transferable and with the Hypnose andcertain welfare procedures (Mesmer cancellations) a role to play should.

Magnetism as metaphor

colloquial is used the term magnetism also for human behaviors. One speaks of the fact that someone by an attractive person or thing is magnetically tightened. A “spectator magnet” is a thing, with which the people remain standing and them to regard.

See also

Web on the left of

Wiktionary: Magnetism - word origin, synonyms and translations
 

  > German to English > de.wikipedia.org (Machine translated into English)