Talk:Permeability (electromagnetism)

message: * Permittivity, permeability - these should be explained more thoroughly; in particular, it's unclear what any of these mean.  --ᓛᖁ[ ᑐ] 14:36, 6 Nov 2004 (UTC)
thread_title:  From PNA/Physics 

message: You can find more information at the web-page
:History of the Ampere
The factor of 10^-7 arises mainly because of the transition from CGS to SI units.
:10^-5 going from a dyne to a newton of force.
  
:10^-2 going from an abampere to an ampere (because it flows in both conductors).
Or something like that.
The "practical units of electricity" have nothing to do with cgs (since they are older than cgs in any case).  The practical electrical units displaced older ones like 'a geographic mile of no. 6 copper wire', and various cells of particular construction.  The new system did not prevent the old constructions, but stated that the results should be expressed in terms of a particular decade-multiple of the metric-electrostatic system.  The system in use at the time was Metre-gram-second.
The size of the resistance unit (ohm) was selected to be as near that of the siemens unit (a column of mercury, 1 mm² in section, and 1 metre long), and the potential that nearest the daniels cell.  Maxwell showed that the required system to make this happen was to have a length of 10,000 km, and a mass of 10 picograms, along with the second.  The value of 10-7 comes, because the henry (in emu, a length of 10,000 metres), gives 1 henry/(10,000 km), or 10-7 henry (ie 10,000 km) / metre.   
The 'practical' bit was because they were intended to be used in practical use, like wiring up houses etc.  They were always intended to be perfect multiples of the theoretical EMU.  It's much like the practical unit of speed is km/h or mph, while the theoretical unit is m/s or f/s.  The former is practical for driving cars, the latter is the 'coherent unit'.
The 'international' bit is to deal with the constructions outside of the definition.  This has nothing to do with the intended size of the unit, but what is the 'best way' of creating measures that could be used for calibration etc.   In much the same way, one hears talk of 'conventional', which refers to the most exact way of producing units.  The errors in the CODATA tables is due to the inexactutde in reproducing the theoretical definitions from the implementations, not from the implementation themselves. 
A proposal exists to redefine the ampere as x electrons per second, and the kilogram in terms of planck's constant.  Under such a definition, the size of the permittivity constant comes to errors in the fine structure constant, since the resistance unit will become h/e², which is 137.036 times the current resistance of 29.9792458 (ie 10-7 c).  The permeability will then have an error equal to that of that of the fine structure constant.  08:36, 4 October 2011 (UTC)
thread_title:  History of the Ampere

message: I don’t know what difference it makes, but μ and µ are two different characters. The only difference I see (and only in some fonts) is that µ is slanted and μ isn’t. In the Unicode character palette, µ (0x00B5) was found under Symbols > Letterlike Symbols, and μ (0x03BC) under European Scripts > Greek. I changed all the mus in the article to the former, which is the one I can type (option-M on a Mac). If it makes any difference and I’m in the wrong, change them all to the other μ. —Frungi 06:58, 29 September 2006 (UTC)
replies: text: U+00B5 is "MICRO SIGN", so I think when you say "μ = 1.26 µN A-2", the first μ should be U+03BC because it's the Greek letter being used as a variable, but the second µ should be U+00B5 because it stands for 10−6. —Keenan Pepper 06:31, 30 September 2006 (UTC)
thread_title:  μ vs µ 

message: If one puts the ferromagnetic material into an externally applied magnetic field, the domains tend to line up, so that the sum of the fields from the ferromagnet and the resulting magnetic field is higher in magnitude than the applied magnetic field alone.
I suggest that the word "applied" would make more sense, otherwise it could be read that the ferromagnet field is included twice.
Alternatively, it could be rewritten "so that the resulting magnetic field is higher in magnitude than the externally applied magnetic field alone."
I have not made the change as this needs to be confirmed by an academic who should make the change. Just Maybe 23:27, 27 May 2007 (UTC)
thread_title:  Usage of the word "resulting" in the following 

message: Just before the explanation for why there is no error in the figures comes reasons why there should be. I see nothing in SI units and mathematic definitions that keep error out of real-world experimental results. Brewhaha@edmc.net 06:17, 17 July 2007 (UTC)
thread_title:  No Estimation of Error 

message: I am copying from the Wikipedia page on magnetic permeability:
According to the definition of the auxiliary field, H
B=μ(H+M)
 
where
μ is the material's permeability, measured in henries per meter. 
B is the magnetic field (also called the magnetic flux density or the magnetic induction) in the material, measured in teslas 
H is the auxiliary magnetic field, measured in amperes per metre 
M is the magnetic moment per unit of volume or magnetization, measured in teslas 
How can you add H and M in the parenthesis if they have different units? (H has A/m,
M has teslas).
This doesn't look right.  —Preceding unsigned comment added by 77.49.235.14 (talk) 16:47, 30 October 2007 (UTC)
thread_title:  Units problem 

message: http://www.ti.com/lit/ml/slup124/slup124.pdf suggests that while the figure we quote for manganese-zinc ferrites is about right, nickel-zinc ferrites are suitable for somewhat higher frequency use.  Could somebody who knows more about this stuff than me see if this makes sense? 212.159.69.4 (talk) 11:20, 5 February 2012 (UTC)
thread_title:  Max frequency for ferrites 

message: The values of applied field at which these permeabilities are supposedly measured seem extremely suspicious, considering that metglas datasheets (e.g. []) suggest the material has a saturation flux density just over half a Tesla.  The 1,000,000 relative perm claimed on the site doesn't specify the field, and probably refers to 0.5A/m, which is a very small fraction of a Tesla.  Someone more familiar with metglas should really verify this one, since nearly everything I know of starts going into saturation well below half a Tesla. 66.108.191.72 (talk) 10:07, 5 September 2012 (UTC)
thread_title:  Metglas and Nanoperm Claims 

message: Can someone add the characteristics of amumetal to the table?
That's amumetal, not mu-metal.
Thanks.  — Preceding unsigned comment added by 150.195.9.61 (talk) 22:01, 31 January 2013 (UTC)
thread_title:  Amumetal? 

message: relative permeability (µr) is =µ/µ0
So if i take it litterally : µ=µr*µ0
BUT, if i take Carbon steel : µ=100*4pi*10^-7= 1.2566*10^-4, and not "8.75×10−4",
So , did i missed something or just an error ?
Thanks  — Preceding unsigned comment added by 213.139.124.12 (talk) 14:55, 21 November 2013 (UTC)
thread_title:  Relative permeablity, µ/µ0 

message: Currenty citation 35 simply says "by definition". This should be in the table entry or as a note below the table to be consistent with other articles. --LonleyGhost (talk) 09:01, 22 June 2020 (UTC)
thread_title:  Use of "by definition" as a reference 

message: Has anyone even read this instead of checking for formatting errors? I gave up on making sense of the article after the fifth physics blunder, and started skimming. Twenty more. 192.180.201.102 (talk) 04:04, 7 March 2024 (UTC)
thread_title:  This is not a physics article !!