Let's Take A Vote...

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Careful there John Fields, Phil Hobbs will plonk you... like you could care :-)

I think I still have the whole thread in "Trash", since I haven't emptied it for awhile. I'll track down the "force" discussion. ...Jim Thompson

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Definitly some of my favorite physics reading. Most of it 'old hat' to you. But even when you know the answer it's fun to see how he gets to it. Feynman always makes it look so easy.

George H.

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My 4*pi was a guess. What's more interesting is the C of an isolated trace with no ground plane near by. (say some high impedance circuit) Do you know how the C scales with the width? Assuming the length is much greater than the width.

George H.

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If you can find where I stated that charges can't cause forces, I'd be interested in seeing the citation. Of course charges attract and repel each other; that's high school physics and plain common sense. What I said is that charge IS NOT force, and that coulombs aren't a measure of force.

Sure. Go for it.

AlwaysWrong has another new friend!

No. It's what college EE and physics courses teach freshmen first semister, because it's so important.

John

Do you mean, like, a microstrip trace on an FR4 board with no ground plane anywhere? Like all such problems, it's messy. If the trace is narrow compared to the dielectric thickness, Er is midway between FR4's (around 4.6 maybe) and air. If the trace is much wider, Er approaches 1.

I have tools to compute L and C per unit length for the common cases, microstrip with ground plane, stripline, CPW, things like that. Your case isn't among them. Easier to measure... if you can decide what to measure *to*

I think Wadell's book covers that case, but his book is pretty much unusable. He has equations that cover a full page, and they include terms that themselves occupy other pages.

John

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Oh, I was thinking about my question, ... Well first it should scale with the length of the trace. (that's pretty obvious) And then I thought there should be some logaritham(sp) of the width vs some other distance... But I couldn't think what distance. It must be the distance from the trace to where ever the nearest ground is... perhaps the walls of the metal box enclosing it.

I wasn't thinking about the dielectric. That should be a secondary effect... as long as the distance to the walls is a lot more than the dielectric thickness.

George H.

It will also depend on whether you treat the dry dusty moon surface as a conductor or a dielectric of mostly basaltic material.

The solar wind is a roughly neutral plasma on average - otherwise the sun would end up charged. Plasmas tend to be on average neutral and fairly good conductors - electrons are far too mobile to allow the heavy nuclei to escape.

Although net charge is even conserved in the production of a black hole a spinning Kerr metric black hole would quickly neutralise any residual bulk internal charge by pair production in its ergosphere and snatching the anti-particles inside and repelling the like charge. This mechanism and a related one involving magnetic fields are thought to power the jets in radio galaxies like Cygnus A and M87. See for example:

Regards, Martin Brown

John F, I've just E-mailed you the portions of the thread that contain the word "force", with headers. So you can peruse it and find what you need. ...Jim Thompson

I checked: Wadell does a lot of weird cases, but not a conductor on dielectric and nothing else. His "covered microstrip" equation is 4 pages long!

Look up ATLC, the free transmission-line calculator. It will solve cases like this.

I think that a big grounded box will be the same as free space, as close as any of the tools can usefully resolve.

John

C goes linearly with radius, and it's conveniently close to 1 pf per cm.

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Thanks John, I'll see what I find. I really should just do the problem for myself from a fundamental physics level. Assume an infinite wire of radius R and calculate the capacitance per unit length.

The 'real' question I have is, does it make sense to make really skinny traces for a high impedance circuit with no ground plane? Sense in that on want to keep the capacitance low.

OK I got down the "Radio Engineers Handbook" by Terman, from my bosses book shelf. (He's an old fart.) Terman does the case of a wire diameter d a height h above a ground plane. For h>>d the capacitance per foot (in units of micro micro Farads) is, C =3D 7.354/log(4h/d)

George H.

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Absolutely. Use the shortest and skinniest traces you can, no planed nearby, no or tiny vias.

Appcad (free from Agilent) does that case, but only gives you Zo and effective Er. I have a little PowerBasic program that converts those values to c and l per inch. You're welcome to it.

Almost any simple equation, like the one above, gets inaccurate at certain geometries. The classic microstrip equation, like in the Moto ECL book, reports negative impedance for wide traces. Appcad is pretty good and will warn you when it isn't. As far as I can tell, many such equations are basically accidental curve fits, not based on much actual physics.

Another nice program is Txline 2003, which does some cases that Appcad doesn't.

I have a bunch of Terman's books, but I am *not* an old fart! Terman apparently was... read "The Inventor and the Pilot" for some dirt.

John

You mean you missed this...

You won't catch this trout with that wilted bit of bait.

Not the whitelist, the kill file. A small select group--even Mr. Many Nyms isn't in it.

Sayonara.

Phil Hobbs

=A0 =A0 =A0...Jim Thompson

=A0 =A0...Jim Thompson

See below for something almost as good as the song links...

I wonder how much charge is being transferred between these various, separated 'bodies'.

Is anything lost between these elements when they transfer "charge" (besides JL)?

Version 16 is a damn sight more complicated than the original plan was. Nobody can complain anymore about cost when they keep piling on complexity. It is getting there, however... It turns out to be the only way to get there after all. It is kind of like Von Braun's decision to use an LOR paradigm for the Moon missions. Turns out the way proposed was the ONLY way, yet it was not *his* way, so he was against it, right up to the last design choice review, and surprised his own team went he agreed to it.

--- I'd sit down and have a beer or shoot a game of pool with him anytime, so it's not a new friendship, and an ampere _can_ be used as a measure of length in a similar way that charge can be used as a measure of force.

I outlined the procedure for current in an earlier post, to which you replied, but couldn't refute, so your gratuitous attempt at casting me in an unfavorable light by associating me with one whom you've labeled "untouchable" was, obviously, just more smoke and mirrors behind which you always try to hide.

Are you ever real or are you, somehow, forced to perpetually play the game of "My dick's bigger than yours?"

I did no such thing. I merely ststed that they are doing the program still and that it has higher efficacy than the last band of nay sayers gave it. That was all and nothing more. Sprinkling in a joke about charge seems to get everyone charged up. Not me. Take a look. Did you even visit the site?

Jeez. When I am mean at folks you are silent, but when I try to say something nice, you too jump on the "He's a UPO" (Unidentified Posting Object) Bandwagon. Jeez. Let it go already. I never said a damned thing about my humongous dick. :-)

Amperes are not meters. Coulombs measure charge, newtons measure force. What's controversial about that?

This has nothing to do with reproductive organs. It has to do with getting SI units right. Did you ever read the wiki piece on dimensional analysis? Do you think it is smoke and mirrors?

So, where did I say that charges can't generate forces? If you can't find such a statement, YOU are the one with emotions clouding your reason.

John

I don't think JF was referring to your impressive masculinity; he was probably referring to mine.

John