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Simple question I don't have the means to test at the moment.

Imagine a flat block magnet about 5cm in length, 1mm thick, 1cm wide. The top face (5 by 1) is North, the lower South.

I then cover this top North face with a long piece of iron, the same width, also say a 1mm thick, but about 20cm long, aligned with the magnet to extend its length to 20cm. The actual magnet position could be, say, the centre of the iron plate.

Does the entire top of the iron plate become North magnetic?

If not, is there some other material or configuration that would allow me to 'spread' the magnetism across the top surface to some significant extent (eg: by a few cm more)?

Thanks in advance to any responders.

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  • $\begingroup$ I'm not qualified to answer, but I think you can learn more about this by Googling for the phrase "magnetic circuit." $\endgroup$
    – Solomon Slow
    Commented Mar 17, 2020 at 15:20
  • $\begingroup$ are you describing refrigirator magnets? physicscentral.com/experiment/physicsathome/zipmagnets.cfm . Thinking with magnetic field lines the answer would be yes for simple poles, the strength diluted, but flat pieces as you describe are not simple poles usually. $\endgroup$
    – anna v
    Commented Mar 18, 2020 at 5:21
  • $\begingroup$ @annav no I was thinking block magnets like this supermagnete.de/eng/block-magnets-neodymium/… $\endgroup$
    – Frank
    Commented Mar 18, 2020 at 5:40

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Does the entire top of the iron plate become North magnetic?

Yes, but the field strength will be diluted because the small area field lines will go to the larger area, but their "number" will be the same. You have a bar magnet with very small length and the lines will be squeezed accordingly.

bar magnet

If you extend the active area by a ferromagnetic plate, the same lines will be distributed, with a weaker density. (All lines are closed, the plot is economic on dimensions.

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