Can a Compass Needle be Magnetized to Any Horizontal Direction?

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    Compass Needle
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Discussion Overview

The discussion revolves around the possibility of magnetizing a compass needle to point in any horizontal direction, rather than just north. Participants explore the implications of magnetization techniques, the behavior of magnetic fields, and the physical properties of materials involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that a compass needle can be magnetized to point in any horizontal direction, contingent on the alignment with a stronger magnetic field.
  • One participant proposes that it is possible to magnetize a piece of iron in a direction not parallel to its long axis, although this idea is met with skepticism.
  • Another participant argues that while magnetization can occur along the length or width of a bar magnet, it may not be feasible to magnetize it in other directions due to the nature of the magnetizing force.
  • It is noted that iron's cubic crystal structure leads to magnetic anisotropy, making it easier to magnetize along certain preferred directions, although magnetization at arbitrary angles is still possible with an energy cost.
  • A participant questions whether oblique magnetization would result in a loss of retained magnetism and suggests using multiple pieces of iron to manipulate the magnetic field during the magnetization process.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of magnetizing a compass needle in various directions, with some asserting it is possible under certain conditions while others argue against it based on physical principles. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants highlight the dependence on the magnetizing force's direction and the inherent properties of the materials involved, which may affect the outcomes of magnetization attempts.

Hornbein
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A compass needle can be magnetized to point to the north. Am I correct in thinking that the needle could have been magnetized to point to any other horizontal direction?
 
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I don't see why you couldn't magnetize a piece of iron so that its field was not parallel to the long axis.
 
Ibix said:
I don't see why you couldn't magnetize a piece of iron so that its field was not parallel to the long axis.
Right, this is what I had in mind.
 
But if you did that, the torque due to an external field would be much less.
I would be inclined to have a plastic disc with an arrow E-W or NE-SW or whatever you want, but keep the long magnet beneath aligned N-S.
 
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Whilst I would agree that a bar magnet can be magnetised along its length or across its width, I don't think it is possible to magnetise it in other directions. This is because the magnetising force, if oblique, can be resolved into vectors along and across the magnet. The vector along the magnet will create more flux than that across it, so the direction of magnetisation will be slewed towards the major axis. On the other hand, magnetising the bar across its width is possible because the magnetising force will be at right angles to the long dimension and not have a longitudinal vector. In summary, the applied magnetising force will always be resolved along the axes of symmetry and this will favour the major axis.
 
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Iron has a cubic crystal structure so exhibits cubic magnetic anisotropy, i.e. it takes less energy to magnetise a sample along the directions parallel to the lattice edges ("easy axes"). You can still magnetise the sample at arbitrary angles to these favoured directions, at an energy cost which goes as sin2.
 
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I'm not sure whether you're saying, you can't magnetise a needle obliquely, or if you can, that it won't retain its magnetism?
If the former, could you not use five carefully shaped pieces of iron to 'fool' the magnetic field into going where you want it whilst magnetising the needle? (3 is the needle.)
And to mitigate the latter problem, use these pieces as 'keepers' ? (That might prejudice its utility as a compass! Though a compass that points on a bearing of 71.5 degrees magnetic, may not be the most useful compass in the world?)
compass.png
 

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