Magic capacitors!
in [Design]
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From: tm on 21 Jul 2010 12:30 "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. 7.3452347821 millifarads. In general. --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: John Larkin on 21 Jul 2010 12:44 On Wed, 21 Jul 2010 12:30:10 -0400, "tm" <noone(a)msc.com> wrote: > >"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. > >7.3452347821 millifarads. > >In general. > 2*pi is often a good guess. So your solution is very close. John
From: tm on 21 Jul 2010 12:54 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:ut8e46h0boouv5ti5gpajvho8k9rb01on3(a)4ax.com... > On Wed, 21 Jul 2010 12:30:10 -0400, "tm" <noone(a)msc.com> wrote: > >> >>"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. >> >>7.3452347821 millifarads. >> >>In general. >> > > 2*pi is often a good guess. So your solution is very close. > At least he didn't ask to show your work. :)\ --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: George Jefferson on 21 Jul 2010 13:17 "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. 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. 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.
From: tm on 21 Jul 2010 13:42
"George Jefferson" <phreon111(a)gmail.com> wrote in message news:i27a3m$qla$1(a)news.eternal-september.org... > > > "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. > 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. > > 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. > > Your math isn't even good enough to be wrong. --- news://freenews.netfront.net/ - complaints: news(a)netfront.net --- |