# B Plotting magnetic field lines between two adjacent NS poles

1. Nov 13, 2016

### magnetics

This question is regarding the magnetic field lines around two abutting alternating poles.
Take two axially magnetised disc magnets and place them next to each other (like tangent circles), so on each side the adjacent or neighboring magnet is of the opposite pole.

By sprinkling iron filings on the surface of these two abutting alternating pole magnets you can see the magnetic field lines closing out by leaving the north pole of one magnet and entering the south pole of the adjacent magnet. That is until you get far enough away from the adjacent magnet, that the field lines now leave the north pole of the magnet, go in the opposite direction and enter the south pole of the same magnet. That is instead of field lines being directed to the opposite pole of the adjacent magnetic body, they are directed to the opposite pole of the same magnetic body (underneath).

Does the point at which the field lines change from being directed to the adjacent magnetic body to the same magnetic body have a name and is it possible to calculate where this point exists assuming both magnets are identical in size and material?

(I hope my description is adequate, let me know if I should add a photo). Thank you.

2. Nov 14, 2016

### Staff: Mentor

I don't think it has a special name. It is possible to simulate the system to find this point, but magnets with a finite size are very tricky to simulate accurately.

3. Nov 14, 2016

### Staff: Mentor

Very interesting. Do nonlinearities in the shape make it hard to do the integrations?
Or what is the source of the difficulty?

4. Nov 14, 2016

### Staff: Mentor

The field geometry is based on the magnetization of the ferromagnetic material, but this magnetization also depends on the fields of other parts of the magnets - which then influences the field again and so on. The first part is easy, the second effect is hard to evaluate.

5. Nov 14, 2016

### magnetics

Thank you mfb.
I guess having vectors come from so many points makes it complex?

If comparing the two fields, i.e. the field lines joining the adjacent magnetic body and the field lines joining the same magnetic body.
Is there a significant difference in their properties and their effects on other particles in their vicinity? Thank you.

6. Nov 14, 2016

### Staff: Mentor

The size of the setup is no problem - a computer can easily handle that with a numerical simulation. Getting the simulation of the solid material right is the challenging part.

Field lines are not physical objects. The field strength and direction depends on the location, but apart from that there is no difference.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted