# Getting the magnetic field as a function of current

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1. Apr 19, 2017

### vogtster

Howdy,

So, I'm curious, is there a general relationship between current input into an electromagnetic and the magnetic field that it generates in space? The trivial example is wrapping a wire around a rod, then sending a current through it which causes a magnetic field.

My set up is a simple circuit, where we have a power supply, resistor, and electromagnet. I want to solve maxwell equations, and I want to find the relationship between B and I, that is B(x,y,z,t,I).

I have Jackson, so if someone could refer me to an area in his book which may explain this, or any other sources I would appreciate it.

2. Apr 20, 2017

### BvU

Jackson isn't very introductory. Hyperphysics is a lot friendlier...

3. Apr 29, 2017

### EnEE

It's may be difficult...
according to general equations it's linear relationship(like here: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html or here: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html)

notice that usually all the computes are in specific area of the space, usually where the integral is easy to solve...
If you want to simulate your magnetic circuit(everywhere in space) you can use this software: http://www.femm.info/wiki/HomePage

but always remember: "In theory there is no difference between theory and practice. In practice there is." and as I saw, especially in elctromagnets there is big difference

4. Apr 29, 2017

### jim hardy

If there's ferromagnetic material involved you have some complications
its memory google hysteresis , retentivity
its own reaction to magnetic field google eddy current, retardation of magetization , magnetorestriction

Bozorth kinda 'wrote the book' on Ferromagnetism

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my two cents, and probably it's overpriced at that.

Last edited: May 1, 2017
5. May 1, 2017