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Re: [Phys-l] transformer question

On 2009, Aug 14, , at 15:35, John Denker wrote:

On 08/13/2009 09:04 PM, Bernard Cleyet wrote:

I was brought up by Mr Harnwell who devotes ~ 13 densely written
pages to the subject, ........

That's good to know. There is an amazing dearth of
references on the subject.

I refer to Harnwell, Eisberg ** and http://www.av8n very often in replying to posts (tap-l, PTSOS, physhare, etc.) [occasionally to Feynman, et al. ]

** Principles of Electricity and Magnetism, Physics, Foundations and Applications

bc thinks J. D. was brought up by Harnwell or similar author.

Me? Absolutely not.


Then in engineering class somebody probably said we have
several inputs and several outputs and a linear system.
It can be described by a __ __ __ __ __ __. Fill in the
blank. It's a six letter word that starts with "M" and
ends with "ATRIX".

Then they said this is called the capacitance matrix. The
off-diagonal elements are the "mutual" capacitances while
the diagonal elements are the "self" capacitances.

This begins on p. 20 (Harnwell) and includes Green's reciprocation theorem.

I had (have) much difficulty with this.

I think they forgot to tell us that because of gauge
invariance there's really no such thing as a self
capacitance. Or (more likely) I slept through that bit.
In any case, I had to figure that bit out on my own,
many years later.


I don't recall hearing or reading anything about non-ideal
transformers or mutual inductances ... but they *did* tell
us "the same equations have the same solutions" and if we
live to be 2000 we will never forget that. And the equations
for inductors are almost the same as the equations for
capacitors, given a trivial change of variables.

On my commenting on the homology of partially frustrated total reflection and alpha decay Bob Eisberg replied, "A wave is a wave is a wave."

I got into finite element modeling so long ago I forget
the first application. I got into FEM applied to non-ideal
magnetic materials when helping my father design a solenoid
valve for some NASA or Air Force rocket.


The details of my story are not important.

The point I'm trying to make is this: I am continually
amazed when people ask me who taught me this-or-that
subject or where I read about it. The answer, 90% of
the time, is that nobody taught me anything about that
subject. They just taught me how to figure stuff out.

You know the proverb about giving somebody a fish versus
teaching them how to catch their own fish.

If you want to see some of the capacitance-related fish
I have caught, see

... but to repeat the main point, I don't recommend you
memorize what it says there; just understand it well
enough so that if/when a similar problem crops up you
will be able to derive whatever you need.

I remember thinking in high school, physics and maths were easier subjects (for me), because I didn't have to memorize so much.

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