Magnetic Field outside a solenoid

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Discussion Overview

The discussion revolves around determining the magnetic field at a distance from a solenoid, specifically in the context of a ferrite rod wound with wire and oscillating at a frequency of 73 kHz. Participants seek equations and methods to calculate the magnetic field strength at various points in space, highlighting the challenges of finding consistent information on this topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in finding reliable information on calculating the magnetic field from a solenoid and requests assistance.
  • Another participant suggests that understanding the properties of ferrite and the magnetic fields it produces is necessary for the calculations.
  • A participant provides a formula for magnetization and discusses the relationship between the magnetic field and the geometry of the ferrite rod, mentioning the use of Legendre polynomials for off-axis calculations.
  • Concerns are raised regarding the need for a magnetically soft ferrite to ensure accurate results, particularly in relation to hysteresis relaxation time.
  • A later participant seeks updates from the original poster on whether they found a solution to their problem, indicating ongoing challenges in finding information on the topic.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on a specific method or equation for calculating the magnetic field, indicating that multiple competing views and uncertainties remain in the discussion.

Contextual Notes

Participants mention various assumptions, such as the uniformity of the magnetic fields and the importance of the ferrite's properties, but these aspects remain unresolved and depend on specific conditions.

Who May Find This Useful

Individuals interested in the calculation of magnetic fields from solenoids, particularly in experimental physics or materials science, may find this discussion relevant.

woje04
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I am a physicist, a young physicist. I can't find information that agrees on how to determine the magnetic field at a distance from a solenoid.

We use a ferrite rod of 7.5" long wound with wire over 6.5" of it. The frequency it oscillates at is 73 kHz. If I know the current how can I determine the magnetic field at any point in space. I have looked everywhere and I get different information everywhere. I need some help.
 
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I suspect that you need some info on the properties/material physics of ferrite and the magnetic fields that it produces first.
 
the ferrite we are using has a permeability of approximately 8000 and the fields we are measuring are very colse to uniform, (possible human error). What I need is an equation that will give me an accurate magnetic field strength at any point away from the solenoid.
 
You can treat the 7.5" ferrite rod as a uniformly magnetized magnet of magnetization
M=\mu nI/c, where n =turns/length, all in Gaussian units.
If the ends of the rod are circular, the B field outside will be the same as the E field due to two uniformly charged disks with surface charge \sigma =+ M and -M.
This field can be found using Legendre polynomials for off axis.
Reasonable approximations can be made if you are close to or far from the rod.
This all depends on the hysteresis relaxation time being small compared with the period of the oscillation. You need a magnetically very soft ferrite.
 
hey woje
did you ever find a way to calculate the field? I'm having the same problems you were with finding information on how to calculate the fields, so if you found anything I would really appreciate your help. Thanks.
 

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