What is the Relative Permeability of Iron in a Solenoid?

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Discussion Overview

The discussion revolves around calculating the relative permeability (μr) of iron in a solenoid using a specific equation. Participants explore the implications of their calculations and the expected values based on experimental data.

Discussion Character

  • Mathematical reasoning
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents an equation for calculating μr and expresses confusion over the discrepancy between their calculated value and the expected value of approximately 200.
  • Another participant claims to obtain a value close to 200 when using the same equation, suggesting a possible error in the first participant's calculations.
  • A third participant points out a potential mistake in the first participant's use of parentheses in the equation, which could affect the calculation.
  • Several participants question the expectation of μr being 200 for the piece of iron, prompting further exploration of the basis for this expectation.
  • One participant mentions that the iron used in a lab experiment is supposed to have a relative permeability of 200, indicating a desire to confirm this value through calculation.
  • Another participant notes that a close match between the calculated and expected values might be coincidental and highlights the distinction between permeability and apparent permeability.

Areas of Agreement / Disagreement

Participants express differing views on the accuracy of the calculations and the expectation of μr being 200, indicating that the discussion remains unresolved regarding the implications of these values.

Contextual Notes

There are potential limitations in the calculations due to missing parentheses, and the discussion touches on the distinction between permeability and apparent permeability without resolving these nuances.

Mason98
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TL;DR
Hello, I was wondering how to tranpose this equation? I am sure that i'm doing it correctly but I am getting a wrong answer. Any help will be much appreciated
So the equation is
L=μoμrN^2A/l

I am wanting to make μr the subject and I think this is how i do it?

μr = L*l/μoN^2A

However when I type in this equation i am expecting to get about 200 for the relative permeability of iron. However, i am getting like 9x10-3 which is nowhere near 200.
For example here are my figures
μo = 4 * pi * 10-7
N^2 = 105^2
A = 0.00196
L= 57 mHenrys
l= 0.095

I assume to get 200 for relative permeability as when i use the first equation using 200 I get that L is 57 mH but when i try tranpose and find μr I don't get 200.

If anyone could help i'd really appreciate it thank you :)
 
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When I plug the values into your equation I get essentially 200 for μr (well, 199.4). I suggest that you check your finger work on your calculator keypad :smile:
 
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gneill said:
I suggest that you check your finger work on your calculator keypad
Specifically, you forgot to put parenthesis "()" around the denominator.

Cheers,
Tom
 
Just out of curiosity: why are you expecting to get μr=200 for your piece of iron?
 
zoki85 said:
Just out of curiosity: why are you expecting to get μr=200 for your piece of iron?
gneill said:
When I plug the values into your equation I get essentially 200 for μr (well, 199.4). I suggest that you check your finger work on your calculator keypad :smile:
Sorted now thanks, was typing it in wrong. lol
 
zoki85 said:
Just out of curiosity: why are you expecting to get μr=200 for your piece of iron?
The Iron I've used in a lab experiment is supposed to be 200 so that's why i wanted to calculate it to confirm
 
Mason98 said:
The Iron I've used in a lab experiment is supposed to be 200 so that's why i wanted to calculate it to confirm
Then such a close match between measured/calculated and expected value I would consider a luck (even in a carefully arranged experiment). Also have on mind the difference between permeability and apparent permeability:
https://en.wikipedia.org/wiki/Solenoid#Quantitative_description
 

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