Magnetic dipole moment of a ferromagnetic cylinder

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Discussion Overview

The discussion revolves around calculating the magnetic dipole moment of a ferromagnetic cylinder, specifically a Nickel cylinder with given dimensions and an external magnetic field. Participants explore the appropriate formulas for this scenario, considering the differences between spherical and cylindrical geometries.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks a formula for the magnetic dipole moment of a cylinder, noting they only have a formula for spheres and are attempting to model the cylinder as a dimer of two spheres.
  • Another participant questions the definition of magnetic dipole moment, suggesting an integral form related to current.
  • A participant clarifies that the integral form is a method to calculate the induced magnetic dipole moment when current is known, but emphasizes the need for a formula specific to ferromagnetic cylinders in an external magnetic field.
  • Concerns are raised about unit discrepancies between the provided formulas, particularly regarding the presence of a \(\mu_0\) factor.
  • One participant suggests that the magnetic domains in the ferromagnetic material will align in the external field, potentially affecting the calculation of the magnetic moment, and questions whether multiplying by the volume of the cylinder would be appropriate.
  • Reference to Griffiths' electrodynamics is made, indicating difficulty in finding relevant information on this topic.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate approach to calculating the magnetic dipole moment for a ferromagnetic cylinder, with no consensus reached on a specific formula or method.

Contextual Notes

Participants note limitations in existing formulas and the need for clarification on how to adapt spherical models to cylindrical geometries, as well as the implications of ferromagnetic properties on the magnetic moment.

amicus_tobias
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I have a Nickel cylinder, 5 micron in diameter and 10 micron in length. I know the external field \vec{B}is 80 gauss, what is the formula for the magnetic dipole moment of this cylinder in the field?

Now I only have the formula for magnetic dipole of spheres, which is \mu = \frac{4}{3}\pi a^3 \chi B, so I sort of make estimates by modeling the cylinder as a dimer of two spheres. But I would like to get a formula particular to cylinders.

Please help. Thank you!
 
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Can someone help here? thanks!
 
when you say magnetic dipole moment
do you mean M= \int I da
 
cragar said:
when you say magnetic dipole moment
do you mean M= \int I da

I think that is just another way to calculate the induced magnetic dipole moment if you know the current flowing. But now I have a magnetic field, I know exactly what it is, and I want to know what is the magnetic moment in a cylinder which happens to be ferromagnetic.
 
The formula i gave and the one you gave have different units.
there off by a \mu_0
So because you have a ferromagnetic material when we place this in an external B field it will cause the magnetic domains to line up and cause the cylinder to have its on B field.
could you just multiply it by the volume of a cylinder or will that not work.
I flipped through Griffiths electrodynamics and couldn't really find anything on it.
 

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