# Magnetic permeability

1. Aug 26, 2007

### thick0122

I was wondering if someone could please explain to me, in layman's terms, what magnetic permeability and relative permeability entails. thankyou

2. Aug 26, 2007

### Idjot

I copied these from the following location. I'm not sure if this qualifies as layman's terms but I've found it helpful in my own recent project where I've been making electromagnets and working with permanent magnets. http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm

1. Retentivity - A measure of the residual flux density corresponding to the saturation induction of a magnetic material. In other words, it is a material's ability to retain a certain amount of residual magnetic field when the magnetizing force is removed after achieving saturation. (The value of B at point b on the hysteresis curve.)
2. Residual Magnetism or Residual Flux - the magnetic flux density that remains in a material when the magnetizing force is zero. Note that residual magnetism and retentivity are the same when the material has been magnetized to the saturation point. However, the level of residual magnetism may be lower than the retentivity value when the magnetizing force did not reach the saturation level.
3. Coercive Force - The amount of reverse magnetic field which must be applied to a magnetic material to make the magnetic flux return to zero. (The value of H at point c on the hysteresis curve.)
4. Permeability, m - A property of a material that describes the ease with which a magnetic flux is established in the component.
5. Reluctance - Is the opposition that a ferromagnetic material shows to the establishment of a magnetic field. Reluctance is analogous to the resistance in an electrical circuit.

The relative permeability is arrived at by taking the ratio of the material's permeability to the permeability in free space (air).

The link above points to one page of a very informative set of pages. Just in case you or anyone else would like to check out the whole thing, here you go. Makes a good bookmark:

http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/cc_mpi_index.htm

Last edited: Aug 26, 2007
3. Aug 26, 2007

### Michael G

length of retension a material will have

Can this be calculated and used as a basis for when the material could be polarized in the opposing field, i.e. from pos to neg

4. Aug 26, 2007

### Idjot

Can what be calculated ?

5. Aug 26, 2007

### Claude Bile

Magnetic permeability is the internal magnetic field induced in a medium divided by the applied magnetic field (technically defined as B/H).

Relative permeability is the magnetic permeability divided by the permeability of free space, mu_0.

Claude.