Is There a More Accurate Equation for the Magnetic Moment of a Solenoid?

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Discussion Overview

The discussion centers on finding a more accurate equation for the magnetic moment of a solenoid that does not rely on the number of turns as an input. Participants explore the relationship between the magnetic field and the magnetic moment, particularly in the context of validating measurements taken from a solenoid with a high number of turns.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks an equation for the magnetic moment of a solenoid that avoids using the number of turns, suggesting the need for a second input for validation through testing.
  • Another participant notes that the magnetic field at one end of a solenoid is half of what is calculated using the standard formula for the magnetic field at the center of a long solenoid.
  • A participant emphasizes that while the standard formula for the magnetic field depends on the number of turns, their concern lies with calculating the magnetic moment using the measured magnetic field.
  • In Gaussian units, one participant proposes the equation for magnetic moment as m=BL/4pi, where B is the magnetic field and L is the length of the solenoid.
  • Another participant corrects the previous equation by including the cross-sectional area, suggesting the magnetic moment should be m=BAL/4pi.
  • A participant raises a concern about the units of the proposed equation, noting that it results in Tm^2 and questioning the absence of the magnetic constant, which could lead to confusion regarding the units of magnetic moment.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate equations for the magnetic moment and the implications of units, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

There are limitations regarding the assumptions made about units and the dependence on the magnetic constant, which have not been fully addressed in the discussion.

Kydharis
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Does anyone have an equation that describes the magnetic moment of a solenoid that does not actually use number of turns as an input?

I'm trying to validate a solenoid I have made with something like 11000 turns, but I'm not sure how accurate my number of turns in, so I need a second input that I can validate through testing (In this case, I can measure the magnetic flux at the poles of the solenoid).

I'm told that using a dipole equation for it is a decent approximation, but I'm really looking for a better approximation than that, since ideally a solenoid only becomes like a dipole at infinity.
 
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The B field on the axis at one end of a solenoid is 1/2 what is given by the standard formula for the B field at the middle of a long solenoid.
 
Yes, but unfortunately the standard formula for the B field of a long solenoid has a
dependence on N (turns).

I actually can measure B of my solenoid - its the magnetic moment I'm concerned about. I want to use the B field I measured to get a magnetic moment.
 
In Gaussian units, the magnetic moment of a solenoid of length L with a field B at its center is m=BL/4pi.
 
I left out the cross-sectional area of the solenoid.
The mag moment should be m=BAL/4pi.
 
The units on that equation are a little weird. Right now, BAL/4pi is Tm^2 (or gauss*M^2). In my experience, magnetic moment is usually given in Am^2. I think the missing link is the magnetic constant - but adding it in with the 4pi leaves us with Am^3.
 

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