Why are the magnetic poles of a magnet are located somewhere within the magnet?

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Discussion Overview

The discussion revolves around the location of the magnetic poles within a bar magnet, specifically why they are considered to be located just inside the ends rather than at the very ends themselves. Participants explore definitions, physical properties, and implications of magnetic pole positioning.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that the poles of a magnet are located at the ends, questioning why others suggest they are positioned within the magnet.
  • There is a suggestion that the definition of magnetic poles may be a point of confusion among participants.
  • One participant notes that the ratio of magnetic length to geometrical length of a bar magnet is typically around 0.85, raising questions about why this ratio is consistent across different magnets.
  • Another participant discusses the concept of "end effects," indicating that magnetic field lines begin to spread out before reaching the physical ends of the magnet.
  • There is a proposal that the positioning of poles can vary based on manufacturing choices and specific applications, such as in sheet magnets with alternating pole arrangements.
  • Concerns are raised about the possibility of determining an objective "magnetic length" for permanent magnets, suggesting that the criteria for such measurements may be subjective.

Areas of Agreement / Disagreement

Participants express differing views on the location of magnetic poles, with no consensus reached on the definitions or implications of magnetic pole positioning. The discussion remains unresolved regarding the nature of magnetic length and its consistency across different magnets.

Contextual Notes

Participants highlight potential limitations in definitions and the subjective nature of measuring magnetic properties, indicating that assumptions about magnetic length may vary based on context.

BIT1749
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Bar magnet...

why are the magnetic poles of a magnet are located somewhere within the magnet,not at the ends?
 
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I'm sorry, but that doesn't make much sense: the entire magnet is a magnet.
 
The poles of all my magnets are at the ends. Why are your magnets different?
 
SteamKing said:
The poles of all my magnets are at the ends. Why are your magnets different?

at the ends but a little inside...why the ratio of magnetic length to geometrical length of a bar magnet is always near 0.85?
 
BIT1749 said:
why are the magnetic poles of a magnet are located somewhere within the magnet,not at the ends?

i asked about poles which are present only at two points,just inside the ends...not all over the magnet...
 
You could make the poles wherever you want. Putting them at the ends is just what manufacturers usually do. If a particular application required them to be at the corners or perhaps some arrangement of multiple poles then that's how they would be made. Take sheet magnets for example, they are usually made with alternating stripes of NSNSNS for the width of the sheet. I'm guessing they do this to create a field that is relatively strong at the surface but diminishes very quickly with distance.
 
A BAR MAGNET has only two poles,north & south,just inside the ends .The ratio of magnetic length to geometrical length is always 0.85...why is not different for different BAR MAGNETS?
 
If you look at the field lines for a bar magnet you can see they start to spread out before leaving the end of the magnet rather than at the very end. It's just an "end effect". If the ends were a different shape it probably wouldn't be 0.85.

If the air was replaced by more iron that would also effect the equivalent length.
 
  • #10
BIT1749 said:
A BAR MAGNET has only two poles,north & south,just inside the ends .The ratio of magnetic length to geometrical length is always 0.85...why is not different for different BAR MAGNETS?
I think what you're talking about is the fact the field lines begin to fan out and curl back in space before the end of the physical magnet, like this:

http://www.bbc.co.uk/bitesize/ks3/science/energy_electricity_forces/magnets_electric_effects/revision/3/

I question whether it's possible to determine an objective "magnetic length" for any permanent magnet, and I suspect whoever came up with that ratio had some specific purpose in mind for which they could stipulate criteria. Regardless, with any magnet, the full intensity does not reach all the way to the ends: some of the lines obviously start to curl back before the ends.
 

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