From: John Woodgate
Subject: Re: Deriving H for magnetic cores
Date: Wed, 18 Dec 2002 18:53:57 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Wed, 18 Dec 2002 19:24:13 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Roy McCammon wrote (in <3E008AB8.141E41D5@mmm.com.DELETETHIS>) about
'Deriving H for magnetic cores', on Wed, 18 Dec 2002:
>Anyway the truth depends on exactly what is meant by
>"contour of constant H"
>I'm not even sure what a "contour of constant H"
>means in a general context. In the specific
>context we were speaking of, H points different
>directions at different points along the contour,
>but we say it is constant in the sense that
>Hz = constant = 0
>Hr = constant = 0
>Hphi = constant = non zero
I'm in favour of using sophisticated math if it's necessary to solve a
problem, even if I don't understand the math. But I don't understand why
you choose a model with 3 dimensional geometry and then get tied in a
knot about interpretation.
I like to use the simplest models that are adequate. In this case,
consider a very long, thin, straight conductor. Ampere, B-S and Laplace
all show you that the H contours are circles centred on the conductor,
and in SI units H = I/2[pi]r.
Now bend, twist, roll up, whatever, your conductor. Can you 'break' the
H-contours by any such process? No.
You can go from the straight conductor to a single-turn loop, and, with
a bit of juggling, you can do rectangular and even triangular loops
(although that made my brane 'urt!). The you can go to long solenoids
and thin multi-turn loops. NONE of this needs vector calculus. With
sufficient confidence gained, THEN you can tackle toroids and things.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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