B Field of Large Ring Magnet Calculation

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Discussion Overview

The discussion centers on the calculation of the magnetic field produced by a large Neodymium N35 ring magnet, specifically addressing the unexpected negative result obtained by one participant. The inquiry involves theoretical and mathematical reasoning related to magnetism.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant reports a negative magnetic field result when calculating the field at a distance from the pole face of a large ring magnet, questioning the validity of this outcome.
  • Another participant suggests verifying calculations by breaking down the formula into individual terms to identify potential errors.
  • A third participant acknowledges the negative result but proposes that it may be due to the low field flux at the center of the ring, indicating that the distance from the magnet affects the field strength.
  • This participant also mentions the idea of using a block magnet formula to approximate the behavior of the ring magnet, expressing a need for a specific function for surface ring magnet strength.
  • A new participant seeks clarification on how to determine the value for the distance variable (z) in a similar problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the calculations or the implications of the negative result. Multiple viewpoints regarding the interpretation of the magnetic field behavior and calculation methods are presented.

Contextual Notes

Participants reference specific parameters and calculations without resolving the underlying assumptions or definitions related to the magnetic field strength of ring magnets.

Who May Find This Useful

This discussion may be useful for individuals interested in magnetism, particularly those exploring the calculations related to magnetic fields of ring magnets and their properties.

jok
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Hi Everyone ,

Can anyone explain why I am getting negative result with a large Neodymium N35 ring Magnet ?

Br: Remanence field, independent of the magnet's geometry
z: Distance from a pole face on the symmetry axis
D: Thickness (or height) of the ring
Ra: Outside radius of the ring
Ri: Inside radius of the ring

Br: 12,300
z: 5mm
D: 10mm
Ra: 360mm
Ri: 330mm

(12000÷2)×((10+5)÷(SQRT((POWER(360,2)+POWER((10+5),2))))−(5)÷(SQRT((POWER(360,2)+POWER((5),2))))−((10+5)÷(SQRT((POWER(330,2)+POWER((10+5),2))))−(5)÷(SQRT((POWER(330,2)+POWER((5),2))))))

I am getting a result of : -15.0893364057539 Gauss .

Does it make sense for such a large magnet ?

Thank you

Screen_Shot_2015_08_17_at_10_15_33_AM.png
 
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Welcome to the PF.

I'd suggest doing it with a calculator and writing down the value of each term individually. Then see if you can spot the error in your (Excel?) formula calculation above.
 
berkeman said:
Welcome to the PF.

I'd suggest doing it with a calculator and writing down the value of each term individually. Then see if you can spot the error in your (Excel?) formula calculation above.

I did.

The results are correct .

Some said it is due to the fact that in the center of the ring there is very little field flux, which make sense . The center Z axis is very much away from the actual magnet.

So far what I came up with is using a block magnet formula to calculate a ring magnet by converting it to liner from circular .

But if there is a function for surface ring magnet strength. it would be very helpful.

Thank you
 
Hi, how did you get your value for z? I'm new to this and trying to work a similar problem, any help would be much appreciated
 

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