Magic capacitors!
in [Design]
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From: Jim Thompson on 21 Jul 2010 20:22 On Wed, 21 Jul 2010 15:47:19 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 21 Jul 2010 16:30:20 -0500, "George Jefferson" ><phreon111(a)gmail.com> wrote: > >> >> >>"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in >>message news:rcie465itdu34iaajm1itdqslepu2i87r6(a)4ax.com... >>> On Wed, 21 Jul 2010 12:14:04 -0700, John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Wed, 21 Jul 2010 12:17:41 -0500, "George Jefferson" >>>><phreon111(a)gmail.com> wrote: >>>> >>>>> >>>>> >>>>>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>>>>message >>>>>news:dj7e465sga7fe3nq7hfl3f0uk601pvrem8(a)4ax.com... >>>>>> On Wed, 21 Jul 2010 11:19:31 -0500, "George Jefferson" >>>>>> <phreon111(a)gmail.com> wrote: >>>>>> >>>>>>> >>>>>>> >>>>>>>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>>>>>>message >>>>>>>news:s43e46la1p1vt11527eg3ptl9ulm44dfrj(a)4ax.com... >>>>>>>> On Wed, 21 Jul 2010 07:54:03 -0500, "George Jefferson" >>>>>>>> <phreon111(a)gmail.com> wrote: >>>>>>>> >>>>>>>>>Suppose you have two capacitors connected as >>>>>>>>> >>>>>>>>>--*-- >>>>>>>>>| | >>>>>>>>>C1 C2 >>>>>>>>>| | >>>>>>>>>----- >>>>>>>>> >>>>>>>>>where * is a switch. >>>>>>>>> >>>>>>>>>What is the total energy before and after the switch is closed(in >>>>>>>>>general). >>>>>>>> >>>>>>>> Energy is conserved, so it's the same, if you account for all the >>>>>>>> manifestations of energy. >>>>>>>> >>>>>>> >>>>>>>You didn't answer the question. I assume this because you don't know. >>>>>>> >>>>>> >>>>>> State the question unambiguously and I will. >>>>>> >>>>>> As I said, the puzzle is both ancient and trivial, so probably JT >>>>>> invented it. There are web sites and even academic papers devoted to >>>>>> it. Given all that, how could I not understand it? >>>>>> >>>>> >>>>>Um you don't get it. Your ignorance in basic electronics amazes me. >>>> >>>>That's funny. But people can choose to be amazed in all sorts of ways. >>>> >>>> >>>> Michael >>>>>got it(although he didn't explain where the energy went but I think gets >>>>>it). >>>>> >>>>>Assume the second cap is initially "uncharged" and has the same >>>>>capacitance >>>>>as the first. >>>>> >>>>>Then the initial energy is >>>>> >>>>>Wi = 1/2*C*V^2 >>>>>Wf = 2*1/2*C*(V/2)^2 = 1/4*C*V^2 = 1/2*Wi >>>>> >>>>>Hence the final energy of the system 1/2 what we started with. >>>> >>>>Miraculous calculation. Yours and about 300 web sites that admire this >>>>puzzle. >>>> >>>>You didn't wxplain where the energy went - see those 300 web sites - >>>>but you are assuming losses. Another solution is that no energy is >>>>lost, and it rings forever, in which case the final state that you >>>>cite never happens. The exact waveforms are actually interesting. >>>> >>>>> >>>>>I'd really like to hear your explanation but I know thats impossible(as >>>>>you'll steal someone elses). After all your the one that believes charge >>>>>isn't conserved... heres your change to *prove* it. >>>>> >>>>> >>>>> >>>> >>>>Check my previous posts. I noted the exact waveform across a resistive >>>>switch, for any values of C1 and C2, and an independent way to compute >>>>the energy lost in that switch. >>>> >>>>Given an inductor, one can move all the energy from one charged cap to >>>>another, uncharged one. If the C values are unequal, the C*V (charge) >>>>on the first cap obviously becomes a different C*V on the second one. >>>>I noted that here some weeks ago, too. >>>> >>>>This is all EE101 stuff. >>>> >>>>John >>> >>> Let the hedging begin... >>> >>> In Message-ID: <3b893612tjjndo8o4v1evro050nonjgp41(a)4ax.com> >>> >>> You said: >>> >>> "Right. If you dump all the energy from one charged cap into another, >>> discharged, cap of a different value, and do it efficiently, charge is >>> not conserved." >>> >>> Note the NOT CONSERVED. >>> >>> Now you say, "...the C*V (charge) on the first cap obviously becomes a >>> different C*V on the second one". >>> >>> Where did the charge come from/go to? >>> >>> John "The Bloviator" Larkin is totally incapable of admitting error. >>> >>> I truly suspect you're too ignorant to understand :-( >>> >> >>I'm glad my post got what it was suppose to get out. I kinda feel like >>Breitbart. >> > >Initial condition: > >C1 2F, 1 volt, 1 joule, 2 coulombs > >C2 1F, 0 volts, 0 joules, 0 coulombs > >Now remove all the energy from C1 and deliver it to C2. An inductor >will move the energy nicely. > >Now > >C1 has 0 volts, 0 joules, 0 coulombs > >C2 has 1.414 volts, 1 joule, 1.414 coulombs. > > > >John > Where did the 0.707 coulombs "go", John? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Only as good as the person behind the wheel.
From: markp on 22 Jul 2010 07:01 "George Jefferson" <phreon111(a)gmail.com> wrote in message news:i26qld$1qc$1(a)news.eternal-september.org... > Suppose you have two capacitors connected as > > --*-- > | | > C1 C2 > | | > ----- > > where * is a switch. > > What is the total energy before and after the switch is closed(in > general). > > If you want to make it easier assume C2 is initially discharged. > > Is the energy before and after the same? If not explain why and why it is > not a violation of the conservation of energy law. The simple answer is that for zero resistance and zero inductance the voltage and current would have to be in phase, so as you switch there's an instantaneous drop in voltage across a zero ohm resitor and hence infinite current for an infinitesimily small time. There is no solution in this case. Mark.
From: whit3rd on 22 Jul 2010 10:52 On Jul 21, 10:59 am, "George Jefferson" <phreon...(a)gmail.com> wrote: > "Tim Williams" <tmoran...(a)charter.net> wrote in message > > Wrong -- the inductance and resistance of the circuit is unspecified, so > > 1., there is no correct answer, and 2. it's a nonphysical circuit, so not > > only is it unspecified, it's meaningless. > WRONG. That has nothing to do with it. We can "specify" that the inductance > and resistance is 0. Just because this is physically not possible does not > mean we cannot create such a hypothetical mathematical model. A 'hypothetical mathematical model' doesn't have to conserve energy or charge or correspond to reality. That makes it ... uninteresting. Any transfer of electrical energy is accompanied by a Poynting vector which means the B fields are NOT zero, and that means negligible inductance is never physical. Negligible resistance is sometimes possible, though (superconducting resonators have Q values in the tens of thousands).
From: John Larkin on 22 Jul 2010 11:34 On Wed, 21 Jul 2010 12:59:58 -0500, "George Jefferson" <phreon111(a)gmail.com> wrote: > > >"Tim Williams" <tmoranwms(a)charter.net> wrote in message >news:azG1o.20990$lS1.2654(a)newsfe12.iad... >> "Michael F�rtsch" <michael.foertsch(a)chello.at> wrote in message >> news:57c17$4c46f981$5472c223$14009(a)news.chello.at... >>> The total electrical energy after the charge has been transfered is 50% >>> of the electrical energy that was stored in C1. The residual 50% had >>> been handed to the government as a charge transfer tax. >> >> Wrong -- the inductance and resistance of the circuit is unspecified, so >> 1., there is no correct answer, and 2. it's a nonphysical circuit, so not >> only is it unspecified, it's meaningless. > >WRONG. That has nothing to do with it. We can "specify" that the inductance >and resistance is 0. Just because this is physically not possible does not >mean we cannot create such a hypothetical mathematical model. > > Mathematicians have a sensible way to deal with singularities; they just say "that's undefined." Sure, create your model. Compute 1/0. Enjoy. John
From: Dirk Bruere at NeoPax on 23 Jul 2010 13:04
On 21/07/2010 18:59, George Jefferson wrote: > > > "Tim Williams" <tmoranwms(a)charter.net> wrote in message > news:azG1o.20990$lS1.2654(a)newsfe12.iad... >> "Michael F�rtsch" <michael.foertsch(a)chello.at> wrote in message >> news:57c17$4c46f981$5472c223$14009(a)news.chello.at... >>> The total electrical energy after the charge has been transfered is 50% >>> of the electrical energy that was stored in C1. The residual 50% had >>> been handed to the government as a charge transfer tax. >> >> Wrong -- the inductance and resistance of the circuit is unspecified, >> so 1., there is no correct answer, and 2. it's a nonphysical circuit, >> so not only is it unspecified, it's meaningless. > > WRONG. That has nothing to do with it. We can "specify" that the > inductance and resistance is 0. Just because this is physically not > possible does not mean we cannot create such a hypothetical mathematical > model. And do we also assume it does not oscillate nor radiate? -- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.blogtalkradio.com/onetribe - Occult Talk Show |