# Magnetic field around a wire near ferrous materials

1. Jul 11, 2015

### EddieP

I was wondering if I could ask a question on the magnetic field surrounding a current-carrying wire, and how this field might change with the presence of other, ferrous materials nearby.

I have been using this web page
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html#c3
to calculate the magnetic field around the wire, which the page shows moving in concentric circles.
The site gives the formula B = (μ0*I)/(2*pi*r) Where I is the current in Amperes, and r is the distance from the wire in meters.
This formula is for a wire surrounded by air, but I am wondering what might happen if some other objects were close to the wire (as close as r in the formula)

I am interested in a situation where a high permeability object and a low permeability object are positioned equal distance from the wire.
I am assuming the presence of the high permeability material would make the magnetic field around the wire stronger.
Would the field would still flow in a concentric circle, or would the field be diverted in the direction of the high permeability material?
If the goal was to exert a stronger force on the low permeability object, would the resulting magnetic field have a stronger effect on the low permeability object?

2. Jul 11, 2015

### Hesch

The magnetic field will be distorted. Think of if you have to travel some ( long ) distance by car, you will prefer to use the highway for a long distance, though the total distance ( distance on highway + distance on smaller roads ) may become some longer. You are choosing the fastest way, not the shortest.

The material with the high permeability is the highway, air is the smaller road.

3. Jul 11, 2015

### Hesch

Yes, because the path through the air has been shortened a bit, thus the field strength of the magnetic field, measured in the unit [ A/m ], has increased outside the object with high permeability, and thus at the location of the low permeability object. ( I don't know if that is understandable? ).