Let's Take A Vote...
in [Design]
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From: George Herold on 25 Jul 2010 23:14 On Jul 25, 8:54 am, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > George Herold wrote: > >>>> John > >>>> [1] extra credit: how big would they be? > >> Objects have both self-capacitance and mutual capacitance, so it's quite > >> sensible to talk about a capacitor with only one lead. In Gaussian > >> units, the self-capacitance of an isolated sphere of radius r > >> centimetres is r. (The CGS unit of capacitance is the centimetre.) > > >> One cm ~= 1.12 pF, so 330,000 pF is about 30 km radius. That's quite a > >> big reel! > > >> - Show quoted text - > > > (Or get Phil to check my math.) > > > George H. > > He's having enough trouble with his own recently--it took two tries this > time. > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510 > 845-480-2058 > hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text - > > - Show quoted text - 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.
From: John Larkin on 25 Jul 2010 23:24 On Sun, 25 Jul 2010 20:04:07 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Sun, 25 Jul 2010 12:40:12 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Sun, 25 Jul 2010 13:26:21 -0500, John Fields >><jfields(a)austininstruments.com> wrote: >> >>>On Sun, 25 Jul 2010 07:58:37 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Sun, 25 Jul 2010 02:10:02 -0500, John Fields >>>><jfields(a)austininstruments.com> wrote: >>>> >>>>>On Sat, 24 Jul 2010 15:46:37 -0700, John Larkin >>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>>On Sat, 24 Jul 2010 16:50:09 -0500, John Fields >>>>>><jfields(a)austininstruments.com> wrote: >>>>>> >>>>>>>On Sat, 24 Jul 2010 13:48:57 -0700, John Larkin >>>>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>> >>>>>>>>On Sat, 24 Jul 2010 15:23:53 -0500, John Fields >>>>>>>><jfields(a)austininstruments.com> wrote: >>>>>>>> >>>>>>>>>On Sat, 24 Jul 2010 10:32:36 -0700, John Larkin >>>>>>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>>> >>>>>>>>>>On Sat, 24 Jul 2010 12:25:15 -0500, John Fields >>>>>>>>>><jfields(a)austininstruments.com> wrote: >>>>>>>>>> >>>>>>>>>>>On Sat, 24 Jul 2010 10:13:48 -0700, John Larkin >>>>>>>>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>>>>> >>>>>>>>>>>>On Sat, 24 Jul 2010 11:49:38 -0500, John Fields >>>>>>>>>>>><jfields(a)austininstruments.com> wrote: >>>>>>>>>>>> >>>>>>>>>>>>>On Sat, 24 Jul 2010 08:30:43 -0700, John Larkin >>>>>>>>>>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>>On Sat, 24 Jul 2010 09:04:41 -0500, John Fields >>>>>>>>>>>>>><jfields(a)austininstruments.com> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>>On Sat, 24 Jul 2010 08:15:03 -0500, John Fields >>>>>>>>>>>>>>><jfields(a)austininstruments.com> wrote: >>>>>>>>>>>>>>>On F>> >>>>>>>>>>>>>>>>On Fri, 23 Jul 2010 17:38:45 -0700, John Larkin >>>>>>>>>>>>>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>>>>>Charge is measured in coulombs. Force is measured in newtons. So how >>>>>>>>>>>>>>>>>is charge "a measure of force"? >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>--- >>>>>>>>>>>>>>>>news:2apl46hr8s01os8dv1aipdm19bcf64nec4(a)4ax.com >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>--- >>>>>>>>>>>>>>>Oh, and the first sentence of the cited Wikipedia article reads: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>"Electric charge is a physical property of matter which causes it >>>>>>>>>>>>>>>to experience a force when near other electrically charged matter." >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>JF >>>>>>>>>>>>>> >>>>>>>>>>>>>>If you experience a pig, does that make you a pig? >>>>>>>>>>>>> >>>>>>>>>>>>>--- >>>>>>>>>>>>>That's just a silly diversionary tactic; measuring a force doesn't >>>>>>>>>>>>>make you the force. >>>>>>>>>>>>>--- >>>>>>>>>>>>> >>>>>>>>>>>>>>Look at the SI units if you want to determine if things are the same. >>>>>>>>>>>>> >>>>>>>>>>>>>--- >>>>>>>>>>>>>That's just another silly diversionary tactic. >>>>>>>>>>>> >>>>>>>>>>>>Were you ever taught dimensional analysis? >>>>>>>>>>>> >>>>>>>>>>>>Obviously not. Give it a try: >>>>>>>>>>>> >>>>>>>>>>>>http://en.wikipedia.org/wiki/Dimensional_analysis >>>>>>>>>>>> >>>>>>>>>>>>The basic concept is that you can test all sorts of relationships for >>>>>>>>>>>>plausibility by reducing their SI units. If the units don't agree, the >>>>>>>>>>>>things can't be equal. Newtons aren't coulombs, so charge can't be >>>>>>>>>>>>force. >>>>>>>>>>> >>>>>>>>>>>--- >>>>>>>>>>>No one said it was. >>>>>>>>>> >>>>>>>>>> >>>>>>>>>>You did: >>>>>>>>>> >>>>>>>>>>>>On the other hand, if Larkin's right and energy is conserved but >>>>>>>>>>>>charge isn't, then since charge is a measure of force, unbalanced lost >>>>>>>>>>>>charge might be able to be used for propulsion. >>>>>>>>> >>>>>>>>>--- >>>>>>>>>Ah, now I see. >>>>>>>>> >>>>>>>>>You can't tell the difference between: "charge is force" and: "charge >>>>>>>>>is a measure of force." >>>>>>>>> >>>>>>>>>JF >>>>>>>> >>>>>>>> >>>>>>>>You might read this >>>>>>>> >>>>>>>>http://en.wikipedia.org/wiki/Dimensional_analysis#Commensurability >>>>>>>> >>>>>>>>since it's the easiest part of the article to understand. >>>>>>>> >>>>>>>>Engineers do sometimes break the rules and add non-commensurable >>>>>>>>units, like designing a foldback power supply that limits the sum of a >>>>>>>>voltage and a current. Addition is a poor substitute for >>>>>>>>multiplication, but it's a lot easier to do with cheap parts. >>>>>>> >>>>>>>--- >>>>>>>Yawnnnnnn... >>>>>>> >>>>>>>And, has nothing to with the _fact_ that charges attract or repel each >>>>>>>other and that those attractions and repulsions are _mechanical_ in >>>>>>>nature and can be measured using any convenient system and converted >>>>>>>into any other convenient system as required. >>>>>>> >>>>>>>You do agree that one newton is equal to about 0.1020 kg wt or 0.2248 >>>>>>>pounds avoirdupois, yes? >>>>>>> >>>>>> >>>>>>"kg wt" is not an SI unit, so no. The units don't conform, so the >>>>>>quantities can't be equal. SI units were inventented to clarify things >>>>>>like this. >>>>>> >>>>>>If by "pounds avoirdupois" you mean lbf, pounds force, yes. The >>>>>>relation there is a dimensionless scaler, so is OK. >>>>> >>>>>--- >>>>>As usual, you try to dodge the point, which is that electric charges >>>>>generate mechanical forces, by trying to steer the discussion into >>>>>blind alleys. >>>> >>>>Charges CAN generate force, under certain conditions, but charges ARE >>>>NOT forces. The qualification "certain conditions" means that knowing >>>>charge alone is insufficient to determine any force. Two like charges >>>>in space repel, but you can't know how much unless you know the >>>>distance between them. You need to know the coulombs AND the meters >>>>distance between them to calculate force. So coulombs aren't force, >>>>and you can't measure force in coulombs. The dimensional units just >>>>don't work. >>> >>>--- >>>What a disgustingly patronizing, intellectually dishonest excuse for a >>>scientist you are. >> >>I'm an engineer. Engineer<>Scientist. Incommensurable units again. > >--- >Not at all, since just as in: "All squares are rectangles, but all >rectangles aren't squares.", all engineers are scientists but not all >scientists are engineers. > >In either case, they can be compared. >--- > >>>You were the one one who started this whole thing by claiming that >>>charges don't exert force, and then when I come up with proof that >>>they do you immediately start prosyletizing, pretending that _I'm_ the >>>one who needs to be converted and you're the one who's always known >>>the truth. >> >>I didn't say that charges don't cause forces. > >--- >Yes, you did, and someone else also remarked on it by stating that >you'd be surprised if you knew the force a couple of one coulomb like >charges exerted on each other at a close distance. > >I've lost track of where lies in the thread or if it's even in this >thread, buit if you'll agree to take responsibility for it and own up >to the error, I'll be happy to go look for it. 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. > >Deal? Sure. Go for it. >--- > >>I said that charges can >>generate force, many times now, including just above. > >--- >Sure, _now_ you say it because you realized you were wrong at first >and now you're trying to spin it as though you never said otherwise >and the error never existed. >--- > >I said that chargs IS NOT force, and that a coulomb is not a measure >of force. > >--- >The former is true, but not the latter, in the same sense that an >ampere _can_ be used as a measure of length. AlwaysWrong has another new friend! >--- > >>What's wrong about that? > >--- >The fact that you're pretending your current stance is the same as >your original. >--- > >>One beauty of dimensional analysis is this: if force is measured in >>newtons, and you have coumombs, the requirement that equated things >>have commensurable units means you have to go out and scrounge more >>measurements before you have enough to compute force, and dimensional >>analysis suggests what other things you need to measure. If you >>haven't measured enough other things to make the units align, you KNOW >>that any calculated result is bogus. >> >>Of course, you can still maks a dimensionless scalar error; DA doesn't >>protect against that. > >--- >As you're so fond of saying: "Word salad." No. It's what college EE and physics courses teach freshmen first semister, because it's so important. John
From: John Larkin on 25 Jul 2010 23:40 On Sun, 25 Jul 2010 20:14:06 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jul 25, 8:54�am, Phil Hobbs ><pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> George Herold wrote: >> >>>> John >> >>>> [1] extra credit: how big would they be? >> >> Objects have both self-capacitance and mutual capacitance, so it's quite >> >> sensible to talk about a capacitor with only one lead. �In Gaussian >> >> units, the self-capacitance of an isolated sphere of radius r >> >> centimetres is r. �(The CGS unit of capacitance is the centimetre.) >> >> >> One cm ~= 1.12 pF, so 330,000 pF is about 30 km radius. �That's quite a >> >> big reel! >> >> >> - Show quoted text - >> >> > (Or get Phil to check my math.) >> >> > George H. >> >> He's having enough trouble with his own recently--it took two tries this >> time. >> >> Cheers >> >> Phil Hobbs >> >> -- >> Dr Philip C D Hobbs >> Principal >> ElectroOptical Innovations >> 55 Orchard Rd >> Briarcliff Manor NY 10510 >> 845-480-2058 >> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text - >> >> - Show quoted text - > >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. > 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
From: George Herold on 25 Jul 2010 23:51 On Jul 25, 11:40 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Sun, 25 Jul 2010 20:14:06 -0700 (PDT), George Herold > > > > > > <gher...(a)teachspin.com> wrote: > >On Jul 25, 8:54 am, Phil Hobbs > ><pcdhSpamMeSensel...(a)electrooptical.net> wrote: > >> George Herold wrote: > >> >>>> John > >> >>>> [1] extra credit: how big would they be? > >> >> Objects have both self-capacitance and mutual capacitance, so it's quite > >> >> sensible to talk about a capacitor with only one lead. In Gaussian > >> >> units, the self-capacitance of an isolated sphere of radius r > >> >> centimetres is r. (The CGS unit of capacitance is the centimetre..) > > >> >> One cm ~= 1.12 pF, so 330,000 pF is about 30 km radius. That's quite a > >> >> big reel! > > >> >> - Show quoted text - > > >> > (Or get Phil to check my math.) > > >> > George H. > > >> He's having enough trouble with his own recently--it took two tries this > >> time. > > >> Cheers > > >> Phil Hobbs > > >> -- > >> Dr Philip C D Hobbs > >> Principal > >> ElectroOptical Innovations > >> 55 Orchard Rd > >> Briarcliff Manor NY 10510 > >> 845-480-2058 > >> hobbs at electrooptical dot nethttp://electrooptical.net-Hide quoted text - > > >> - Show quoted text - > > >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. > > 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- Hide quoted text - > > - Show quoted text - 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.
From: Martin Brown on 26 Jul 2010 03:40
On 24/07/2010 21:38, John Larkin wrote: > On Sat, 24 Jul 2010 15:14:41 -0400, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >> Grant wrote: >>> On Sat, 24 Jul 2010 08:51:58 -0700, John Larkin<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>> On Sat, 24 Jul 2010 09:45:53 +0100, Martin Brown >>>> <|||newspam|||@nezumi.demon.co.uk> wrote: >>>> >>>>> On 23/07/2010 23:52, Jim Thompson wrote: >>>>>> Let's Take A Vote... >>>>>> >>>>>> While I write this up, hopefully sometime this weekend, let me ask for >>>>>> votes... >>>>>> >>>>>> How many think, as Larkin opines, "charge is not conserved" ?? >>>>> Hopefully not too many. But it is difficult to predict the behaviour of >>>>> electronics engineers - about half of them think Einstein was wrong :( >>>>>> How many think charge IS conserved ?? >>>>> Just about every physicist on the planet since Ben Franklin. >>>>> >>>>> It was the inconsistency of Ampere's Law with conservation of charge >>>>> that led Maxwell to formulate his famous equations and show that >>>>> oscillating fields of electromagnetic radiation travel at a constant >>>>> speed c in a vacuum. >>>>>> Just curious what I'm up against here. >>>>>> >>>>>> ...Jim Thompson >>>>> A idealised physics version of your original capacitor problem but >>>>> without the switch can be stated as the following problem: >>>>> >>>>> Two identical metal spheres with capacitance C are used. >>>>> Initially one is uncharged and the other with a charge Q >>>>> >>>>> They are brought together from infinity until they touch. >>>>> >>>>> Describe what happens and how the charge is distributed after they are >>>>> in electrical contact. You can add an infinite ground plane under the >>>>> experiment if it makes you feel better about the circuit analogue. >>>>> >>>> Where can I buy 0.33 uF surface-mount metal spheres? Are they >>>> expensive? I'd need ROHS, of course, on reels. [1] >>> >>> Second terminal optional?! >>> >>> But then, we sorta cater to 'monopole' charge when using human >>> body model's charge for anti-static measures. >>> >>> Grant. >>>> John >>>> >>>> [1] extra credit: how big would they be? >>>> >> >> Objects have both self-capacitance and mutual capacitance, so it's quite >> sensible to talk about a capacitor with only one lead. In Gaussian >> units, the self-capacitance of an isolated sphere of radius r >> centimetres is r. (The CGS unit of capacitance is the centimetre.) >> >> One cm ~= 1.12 pF, so 330,000 pF is about 30 km radius. That's quite a >> big reel! >> >> Cheers >> >> Phil Hobbs > > The entire planet is only about a 700 uF cap, but the voltage rating > is pretty good. Bob Pease presided over a debate a few years ago about > the capacitance between the earth and the moon; there were two > distinct values cited, and he came down on the side of the smaller one > and ridiculed the other. I think it depends on whether you do a > 2-terminal or a 3-terminal measurement. One equation approaches zero C > with distance, the other levels off. It will also depend on whether you treat the dry dusty moon surface as a conductor or a dielectric of mostly basaltic material. > > I wonder what the net voltage of "ground" is. Since we keep getting > whacked with solar wind (net protons?) we might actually be heavily > charged. There's a considerable gradient at the surface. 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: http://hera.ph1.uni-koeln.de/~heintzma/k1/CygnusA.htm Regards, Martin Brown |