How do I contain a magnet's magnetic field?

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Discussion Overview

The discussion revolves around methods to contain the magnetic field of a Neodymium Iron Boron magnet, particularly focusing on safety measures to prevent unintended attraction of metal objects. Participants explore various approaches, including physical distance and materials that can shield or contain the magnetic field.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that keeping the magnet at a distance, such as in a medium-sized box, can mitigate the risk of attracting nearby metal objects.
  • Another participant argues that soft iron is effective at "blocking" magnetism, as the magnetic field tends to follow the iron rather than passing through it.
  • There is a contention regarding the nature of magnetic field strength decay, with one participant asserting it follows an inverse square law, while another claims it decreases with the cube of the distance.
  • A later reply acknowledges a mistake regarding the scaling of magnetic fields, indicating that the decay of magnetic field strength has an inverse cube proportionality.
  • One participant shares an experience of receiving magnets packaged with soft iron shields, suggesting practical applications of shielding in shipping and storage.

Areas of Agreement / Disagreement

Participants express differing views on the nature of magnetic field strength decay, with no consensus reached on whether it follows an inverse square or cube law. The discussion includes both agreement on the use of distance and soft iron for containment, but remains unresolved on the specifics of magnetic field behavior.

Contextual Notes

Some statements rely on assumptions about the nature of magnetic fields and their interactions with materials, which may not be universally accepted or fully explored in the discussion.

Magnetism
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I want to buy a Neodymium Iron Boron magnet (N45 or higher), the ones with a very strong pull force. I want to keep it somewhere safe when I'm not doing experiments with it. Is there a way to contain the force so my metals don't fly half way across the room smacking my face along the way? Maybe a box I can put it in? Thanks.
 
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OK, they're not exactly that strong. :rolleyes: The strength of a magnet drops off as the cube of the distance. You don't need to block the magnet so much as you just need some distance. If the magnet has several inches separating it from anything coming close (say, by putting it in a medium-sized box) nothing will be unduly attracted to it.

But that being said, the one thing that best "blocks" magnetism is soft iron. The magnetic field will tend to follow the iron rather than passing through it. However, your implementation is a bit usual - usually you're trying to keep magnetism from affecting something inside a box. i.e. the magnetic field will go around the outside of the box rather than thorugh it.
 
Last edited:
Just reading through. Just noticed one thing that bothered me. Magnetism is an inverse square law, so it wouldn't be the "cube" of the distance. moving two meters away would mean 1/4 of the original field strength.
 
theantivirus said:
Just reading through. Just noticed one thing that bothered me. Magnetism is an inverse square law, so it wouldn't be the "cube" of the distance. moving two meters away would mean 1/4 of the original field strength.
Can you please supply a citation for this? I think it's the cube but I'm willing to be corrected.
 
A monopole field will scale as inverse square. So how will the long range field of two monopoles (= 1 dipole) scale?
 
I am sorry. It appears as though I was thinking about the magnetic monopole, wherever that may exist. The magnetic field strength decay has an inverse cube proportionality. Excuse me for the mistake.
 
I don't remember the web-site where I purchased 8 large NIB magnets, but I do remember how they shipped them.

When I opened the cardboard box, there were 2 U-shaped/square soft iron "shields' that I had to remove(easily), and the NIB's were inside embedded in some type of styrofoam mold.
I'm sure part of this was due to some postal regulation, but I was impressed.
 

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