[eli5] Why do magnetic fields exhibit lines of force, instead of a unified, fuzzy field?


I suppose it is because the things we use to visualize the magnetic field interact with it, and then each other, to clump together like iron filings on a piece of paper–but what about the aurora borealis/australis? So are the lines of force an artifact of visualization?

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The lines of force are an artefact of visualization, but are important to understand because a given section of a field will have an orientation, which is what those lines are depicting, and that orientation determines how it affects other things within that field.

The iron filings line up because they are ferromagnetic.

The filing creates a weak magnetic field when there is no external magnetic field. When you put them in a magnetic field all the part of a single iron filing line up and they create a stronger magnetic field. The filing are themself small magnets.

So they clump together in line because of the magnetic interaction between the filing and the larger magnetic file. So when the filing is there you do ger stronger magnetic field in line with where the filing is.

If the iron filing was not there and you did measure the magnetic file there will not be lined with stronger magnetic,

The way you usually draw the field lines is so it is the distance between them that show hos strong the field is. Because you can draw any number of lines you like regardless of how strong the field is you can only see the relative strength,h not the absolute strength.

Think of the lines of force as a contour map of the magnetic field. The field doesn’t actually have lines anymore than natural ground has flat layers that step up between elevations but the lines are a way of seeing what is going on.

The lines let us see the size and shape of the field, what direction it is oriented in and we can use the spacing of lines to show how quickly the field is changing intensity as you get further away from the magnet (some configurations of magnets can shape the field and make it very strong but very close vs a single magnet that has a larger field with a slower drop in intensity)