# Electromagnet

**an electromagnet** consists of a coil, around which with current flow a magnetic field forms. In that and around the coil is usually an iron core, which leads and strengthens the magnetic field.

The reinforcement of the magnetic field throughferrousmagnetic materials functions only up to their saturation flow density, which is with approximately 1 to 2 Tesla. Very strong electromagnets must be manufactured therefore without nuclear material.

## effect principle

a stromdurchflossener leader trains a magnetic field around itself.

The directionthe magnetic lines of flux can be determined with the being right lp rule: if the leader is thought enclosure in such a way by the hand that the spread thumb points to the direction from the plus to the negative pole (technical direction of current), then the fingers show the directionthe lines of flux of the magnetic field on.

By coil in the same direction of the leader in the coil the magnetic field distributed over the leader concentrates inside the coil and around the coil. A connected resulting magnetic river in oh direction develops for thatCoil.

## theory

for an electromagnetic coil of the length *l* and the number of turns *n*, by which a river *I* flows, computes itself the magnetic field strength *H* too

- < math>

H = I \ \ frac {n cdot} {l} </math>

- and/or. those magnetic flow density
*B*too

- <math>

B = \ mu_ {0} \ cdot \ mu_ {r} \ I cdot \ cdot \ frac {n} {l}. </math>

- In it are <math> \ mu_ {0}< /math> the magnetic field constant and <math> \ mu_ {r}< /math> the permeability of the area umschlossenen of the coil.

- <math>

\ mu_ {0} = 4 \ cdot \ pi \ 10^ cdot {- 7} \ frac {\ mathrm {H}} {\ mathrm {m}}.</math>

In vacuum and/or. in air the relative permeability is <math> \ mu_ {r} = 1 </math>, in ferrousmagnetic materials lies their value between 4 and 15,000 up to reaching the specific saturation point.

## applications

1.: Coil**with**ferrousmagneticCore (usually from iron)

- operating magnets of relays and contactors
- door opener magnet, magnets in buzzers and door gong
- magnetic clutches (z. B. for climatic compressors in KFZ) and brakes (z. B. with reset spring in Rasenmähern)
- of course magnets, thrust magnets
- of lifting magnets (magnet crane in steel plants)
- slipper brake with streetcars
- Magnets to place around switches from rail-mounted vehicles to
- alternating current magnets in diaphragm pumps (z. B. Tire pump for aquariums) and vibratory conveyors
- magnetic field generation in independently excited engines (z. B. Vacuum cleaner) and generators (autogenerator, power station)
- separators for Stofftrennung „ferrousmagnetically “/„not ferrousmagnetically “(z. B. Garbage assortment)
- of deflecting magnets inParticle accelerators and for electron beams (picture tube, electron microscope, electron-beam welding)

2.: Coil **without** ferrousmagnetic nuclear material

- field generation for Wanderfeldröhren
- actuation coil for reed contacts
- superconducting magnets in nuclear spin resonance Tomografen and for research
- uncooled solenoid coils for high field investigations (only burst mode - often the coil must aftereach experiment to be renewed)< p>

*See also:*