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From: John Woodgate
Subject: Re: Problem with magnetic boundary conditions
Date: Fri, 13 Dec 2002 09:35:44 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Fri, 13 Dec 2002 10:06:50 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Chris Carlen
wrote (in ) about 'Problem with magnetic boundary
conditions', on Fri, 13 Dec 2002:
>What is happening with the H? Yes I know that u1 H1n = u2 H2n, but
>that's just the equation. I want to understand if or how the H can be
>affected by the core piece. There is nothing in what I have learned
>from the Biot-Savart Law that indicates that the H could have changed by
>the addition of the core piece. So either the boundary condition is
>right and the Biot Savort Law isn't , or vice/versa.
>Can someone please explain what is going on here?
Consider the magnetic arrangement as analogous to a current source
feeding two resistors in series, one low value (core piece) and one high
value (air path). The voltages across the resistors divide the total
voltage in such a way as to achieve the current match at the junction
between the resistors.
Note that this is a 'gyrated' analogy, in which current maps induction
(B) and voltage maps magnetic field (H). In the magnetic case, the total
available H divides across the core and the air path so as to keep B
constant at the interface. This concept is usually studied in the
configuration of an air-gapped core, in which it's a bit easier to
conceive of the division of H between core and gap.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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