Let's Take A Vote...
in [Design]
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From: John Devereux on 7 Aug 2010 10:56 "markp" <map.nospam(a)f2s.com> writes: > "John Devereux" <john(a)devereux.me.uk> wrote in message > news:87mxth70en.fsf(a)devereux.me.uk... >> Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> writes: >> >>> 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" ?? >>> >>> How many think charge IS conserved ?? >>> >>> Just curious what I'm up against here. >> >> It depends on the context and your definitions, as already pointed out >> and which you still refuse to provide. Are you using a definition which >> says capacitors store charge or not? Is the quantity Q=CV to be regarded >> as "charge" or not? Is charge "delivered" or does it "flow through"? >> >> *Without* any context, I would have said "charge is conserved". You >> don't need to spend three weeks proving this, just point to Kirchoff. >> >> But the context of the original thread was all abouit switched >> capacitors and whether the "capacitors charge" was always conserved when >> transfered to another. We routinely refer to the quantity Q=CV as the >> capacitors "charge", it is this quantity which is not conserved, I.e., >> you can sum them before and after the switching operation and it is >> different. Not sophistry, just a normal use of terms in a circuit >> description. >> >> And it is obvious that this was the intended usage, since otherwise the >> "charge of the capacitor" is always zero! >> >> Basically, our routine use of the word is ambiguous, you can easily >> "prove someone wrong" by assuming the opposite usage to that intended, >> >> -- >> >> John Devereux > > Absolutely right. The way we talk about a 'capacitor's charge', using the > Q=CV equation, relates to the absolute value of charge on each plate, one > plate has +Q charge and the other -Q charge. The net charge on a capacitor > is zero (it has to be, since the same current goes into a capacitor as comes > out while 'charging' it, there can be no net gain or loss of charge inside > the capacitor). > > Therefore the 'capacitor's charge', by the definition above, is not > conserved, but the net charge is. When talking about charge conservation we > have to be careful about what our definitions of what we mean by 'charge' > are. > > I think John actually understands this, it's just the way it's put across > leads others to come to different conclusions. In a quote from a post from > the Magic Capacitors! thread he said to me: "We say that a capacitor stores > charge, the amount being C*V in coulombs, and it works. My whole point, > which has evoked such ranting, is that when you use this convention, be > careful about designing using the concept that (this kind of) charge is > always conserved." Well Thank You and Kudos, Mark, for being one of the few people capable of changing their mind and admitting it. (About their interpretation of what someone else meant, not the physics itself!). -- John Devereux
From: John Larkin on 7 Aug 2010 11:25 On Sat, 07 Aug 2010 15:56:26 +0100, John Devereux <john(a)devereux.me.uk> wrote: >"markp" <map.nospam(a)f2s.com> writes: > >> "John Devereux" <john(a)devereux.me.uk> wrote in message >> news:87mxth70en.fsf(a)devereux.me.uk... >>> Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> writes: >>> >>>> 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" ?? >>>> >>>> How many think charge IS conserved ?? >>>> >>>> Just curious what I'm up against here. >>> >>> It depends on the context and your definitions, as already pointed out >>> and which you still refuse to provide. Are you using a definition which >>> says capacitors store charge or not? Is the quantity Q=CV to be regarded >>> as "charge" or not? Is charge "delivered" or does it "flow through"? >>> >>> *Without* any context, I would have said "charge is conserved". You >>> don't need to spend three weeks proving this, just point to Kirchoff. >>> >>> But the context of the original thread was all abouit switched >>> capacitors and whether the "capacitors charge" was always conserved when >>> transfered to another. We routinely refer to the quantity Q=CV as the >>> capacitors "charge", it is this quantity which is not conserved, I.e., >>> you can sum them before and after the switching operation and it is >>> different. Not sophistry, just a normal use of terms in a circuit >>> description. >>> >>> And it is obvious that this was the intended usage, since otherwise the >>> "charge of the capacitor" is always zero! >>> >>> Basically, our routine use of the word is ambiguous, you can easily >>> "prove someone wrong" by assuming the opposite usage to that intended, >>> >>> -- >>> >>> John Devereux >> >> Absolutely right. The way we talk about a 'capacitor's charge', using the >> Q=CV equation, relates to the absolute value of charge on each plate, one >> plate has +Q charge and the other -Q charge. The net charge on a capacitor >> is zero (it has to be, since the same current goes into a capacitor as comes >> out while 'charging' it, there can be no net gain or loss of charge inside >> the capacitor). >> >> Therefore the 'capacitor's charge', by the definition above, is not >> conserved, but the net charge is. When talking about charge conservation we >> have to be careful about what our definitions of what we mean by 'charge' >> are. >> >> I think John actually understands this, it's just the way it's put across >> leads others to come to different conclusions. In a quote from a post from >> the Magic Capacitors! thread he said to me: "We say that a capacitor stores >> charge, the amount being C*V in coulombs, and it works. My whole point, >> which has evoked such ranting, is that when you use this convention, be >> careful about designing using the concept that (this kind of) charge is >> always conserved." > >Well Thank You and Kudos, Mark, for being one of the few people capable >of changing their mind and admitting it. (About their interpretation of >what someone else meant, not the physics itself!). "Charge " is just a word, and words are subject to different definitions by different people. I don't think many people here would get the reality wrong. Engineers don't always use terms or methods that scientists would approve of. We do what works. When we do cheat the physics, we need to be careful. John
From: j on 7 Aug 2010 13:00 On Aug 7, 8:25 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Sat, 07 Aug 2010 15:56:26 +0100, John Devereux > > > > > > <j...(a)devereux.me.uk> wrote: > >"markp" <map.nos...(a)f2s.com> writes: > > >> "John Devereux" <j...(a)devereux.me.uk> wrote in message > >>news:87mxth70en.fsf(a)devereux.me.uk... > >>> Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My-Web-Site.com> writes: > > >>>> 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" ?? > > >>>> How many think charge IS conserved ?? > > >>>> Just curious what I'm up against here. > > >>> It depends on the context and your definitions, as already pointed out > >>> and which you still refuse to provide. Are you using a definition which > >>> says capacitors store charge or not? Is the quantity Q=CV to be regarded > >>> as "charge" or not? Is charge "delivered" or does it "flow through"? > > >>> *Without* any context, I would have said "charge is conserved". You > >>> don't need to spend three weeks proving this, just point to Kirchoff. > > >>> But the context of the original thread was all abouit switched > >>> capacitors and whether the "capacitors charge" was always conserved when > >>> transfered to another. We routinely refer to the quantity Q=CV as the > >>> capacitors "charge", it is this quantity which is not conserved, I.e., > >>> you can sum them before and after the switching operation and it is > >>> different. Not sophistry, just a normal use of terms in a circuit > >>> description. > > >>> And it is obvious that this was the intended usage, since otherwise the > >>> "charge of the capacitor" is always zero! > > >>> Basically, our routine use of the word is ambiguous, you can easily > >>> "prove someone wrong" by assuming the opposite usage to that intended, > > >>> -- > > >>> John Devereux > > >> Absolutely right. The way we talk about a 'capacitor's charge', using the > >> Q=CV equation, relates to the absolute value of charge on each plate, one > >> plate has +Q charge and the other -Q charge. The net charge on a capacitor > >> is zero (it has to be, since the same current goes into a capacitor as comes > >> out while 'charging' it, there can be no net gain or loss of charge inside > >> the capacitor). > > >> Therefore the 'capacitor's charge', by the definition above, is not > >> conserved, but the net charge is. When talking about charge conservation we > >> have to be careful about what our definitions of what we mean by 'charge' > >> are. > > >> I think John actually understands this, it's just the way it's put across > >> leads others to come to different conclusions. In a quote from a post from > >> the Magic Capacitors! thread he said to me: "We say that a capacitor stores > >> charge, the amount being C*V in coulombs, and it works. My whole point, > >> which has evoked such ranting, is that when you use this convention, be > >> careful about designing using the concept that (this kind of) charge is > >> always conserved." > > >Well Thank You and Kudos, Mark, for being one of the few people capable > >of changing their mind and admitting it. (About their interpretation of > >what someone else meant, not the physics itself!). > > "Charge " is just a word, and words are subject to different > definitions by different people. I don't think many people here would > get the reality wrong. > > Engineers don't always use terms or methods that scientists would > approve of. We do what works. When we do cheat the physics, we need to > be careful. > > John- Hide quoted text - > > - Show quoted text - "When we do cheat the physics" ... interesting concept.
From: John Larkin on 7 Aug 2010 13:18 On Sat, 7 Aug 2010 10:00:38 -0700 (PDT), j <jdc1789(a)gmail.com> wrote: >On Aug 7, 8:25�am, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Sat, 07 Aug 2010 15:56:26 +0100, John Devereux >> >> >> >> >> >> <j...(a)devereux.me.uk> wrote: >> >"markp" <map.nos...(a)f2s.com> writes: >> >> >> "John Devereux" <j...(a)devereux.me.uk> wrote in message >> >>news:87mxth70en.fsf(a)devereux.me.uk... >> >>> Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My-Web-Site.com> writes: >> >> >>>> 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" ?? >> >> >>>> How many think charge IS conserved ?? >> >> >>>> Just curious what I'm up against here. >> >> >>> It depends on the context and your definitions, as already pointed out >> >>> and which you still refuse to provide. Are you using a definition which >> >>> says capacitors store charge or not? Is the quantity Q=CV to be regarded >> >>> as "charge" or not? Is charge "delivered" or does it "flow through"? >> >> >>> *Without* any context, I would have said "charge is conserved". You >> >>> don't need to spend three weeks proving this, just point to Kirchoff. >> >> >>> But the context of the original thread was all abouit switched >> >>> capacitors and whether the "capacitors charge" was always conserved when >> >>> transfered to another. We routinely refer to the quantity Q=CV as the >> >>> capacitors "charge", it is this quantity which is not conserved, I.e., >> >>> you can sum them before and after the switching operation and it is >> >>> different. Not sophistry, just a normal use of terms in a circuit >> >>> description. >> >> >>> And it is obvious that this was the intended usage, since otherwise the >> >>> "charge of the capacitor" is always zero! >> >> >>> Basically, our routine use of the word is ambiguous, you can easily >> >>> "prove someone wrong" by assuming the opposite usage to that intended, >> >> >>> -- >> >> >>> John Devereux >> >> >> Absolutely right. The way we talk about a 'capacitor's charge', using the >> >> Q=CV equation, relates to the absolute value of charge on each plate, one >> >> plate has +Q charge and the other -Q charge. The net charge on a capacitor >> >> is zero (it has to be, since the same current goes into a capacitor as comes >> >> out while 'charging' it, there can be no net gain or loss of charge inside >> >> the capacitor). >> >> >> Therefore the 'capacitor's charge', by the definition above, is not >> >> conserved, but the net charge is. When talking about charge conservation we >> >> have to be careful about what our definitions of what we mean by 'charge' >> >> are. >> >> >> I think John actually understands this, it's just the way it's put across >> >> leads others to come to different conclusions. In a quote from a post from >> >> the Magic Capacitors! thread he said to me: "We say that a capacitor stores >> >> charge, the amount being C*V in coulombs, and it works. My whole point, >> >> which has evoked such ranting, is that when you use this convention, be >> >> careful about designing using the concept that (this kind of) charge is >> >> always conserved." >> >> >Well Thank You and Kudos, Mark, for being one of the few people capable >> >of changing their mind and admitting it. (About their interpretation of >> >what someone else meant, not the physics itself!). >> >> "Charge " is just a word, and words are subject to different >> definitions by different people. I don't think many people here would >> get the reality wrong. >> >> Engineers don't always use terms or methods that scientists would >> approve of. We do what works. When we do cheat the physics, we need to >> be careful. >> >> John- Hide quoted text - >> >> - Show quoted text - > > > >"When we do cheat the physics" ... interesting concept. > Yup. We use math that doesn't actually work, but gets close enough to do the job. We use terminology, like "charge", in our own way. We use empirical properties of things for which we have no theory or explanation. We do simulation and firmware where any concept of proper dimensional analysis is totally lost... just sling the numbers around until it works. We use proper physics when it helps, ignore it when it doesn't. What's interesting is that most physicists are terrible electronic circuit designers, as their journals often show in hilarious ways. One example is their devoted love of jfet differential pairs when the second fet isn't necessary and just multiplies the noise by sqrt(2). And their abiding affection for trimpots, as opposed to proper biasing design. John
From: markp on 7 Aug 2010 13:49
"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:rk4r56l12tj9c75l3osc5heaq7eh417ek8(a)4ax.com... > On Sat, 7 Aug 2010 10:00:38 -0700 (PDT), j <jdc1789(a)gmail.com> wrote: > >>On Aug 7, 8:25 am, John Larkin >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Sat, 07 Aug 2010 15:56:26 +0100, John Devereux >>> >>> >>> >>> >>> >>> <j...(a)devereux.me.uk> wrote: >>> >"markp" <map.nos...(a)f2s.com> writes: >>> >>> >> "John Devereux" <j...(a)devereux.me.uk> wrote in message >>> >>news:87mxth70en.fsf(a)devereux.me.uk... >>> >>> Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My-Web-Site.com> >>> >>> writes: >>> >>> >>>> 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" ?? >>> >>> >>>> How many think charge IS conserved ?? >>> >>> >>>> Just curious what I'm up against here. >>> >>> >>> It depends on the context and your definitions, as already pointed >>> >>> out >>> >>> and which you still refuse to provide. Are you using a definition >>> >>> which >>> >>> says capacitors store charge or not? Is the quantity Q=CV to be >>> >>> regarded >>> >>> as "charge" or not? Is charge "delivered" or does it "flow through"? >>> >>> >>> *Without* any context, I would have said "charge is conserved". You >>> >>> don't need to spend three weeks proving this, just point to >>> >>> Kirchoff. >>> >>> >>> But the context of the original thread was all abouit switched >>> >>> capacitors and whether the "capacitors charge" was always conserved >>> >>> when >>> >>> transfered to another. We routinely refer to the quantity Q=CV as >>> >>> the >>> >>> capacitors "charge", it is this quantity which is not conserved, >>> >>> I.e., >>> >>> you can sum them before and after the switching operation and it is >>> >>> different. Not sophistry, just a normal use of terms in a circuit >>> >>> description. >>> >>> >>> And it is obvious that this was the intended usage, since otherwise >>> >>> the >>> >>> "charge of the capacitor" is always zero! >>> >>> >>> Basically, our routine use of the word is ambiguous, you can easily >>> >>> "prove someone wrong" by assuming the opposite usage to that >>> >>> intended, >>> >>> >>> -- >>> >>> >>> John Devereux >>> >>> >> Absolutely right. The way we talk about a 'capacitor's charge', using >>> >> the >>> >> Q=CV equation, relates to the absolute value of charge on each plate, >>> >> one >>> >> plate has +Q charge and the other -Q charge. The net charge on a >>> >> capacitor >>> >> is zero (it has to be, since the same current goes into a capacitor >>> >> as comes >>> >> out while 'charging' it, there can be no net gain or loss of charge >>> >> inside >>> >> the capacitor). >>> >>> >> Therefore the 'capacitor's charge', by the definition above, is not >>> >> conserved, but the net charge is. When talking about charge >>> >> conservation we >>> >> have to be careful about what our definitions of what we mean by >>> >> 'charge' >>> >> are. >>> >>> >> I think John actually understands this, it's just the way it's put >>> >> across >>> >> leads others to come to different conclusions. In a quote from a post >>> >> from >>> >> the Magic Capacitors! thread he said to me: "We say that a capacitor >>> >> stores >>> >> charge, the amount being C*V in coulombs, and it works. My whole >>> >> point, >>> >> which has evoked such ranting, is that when you use this convention, >>> >> be >>> >> careful about designing using the concept that (this kind of) charge >>> >> is >>> >> always conserved." >>> >>> >Well Thank You and Kudos, Mark, for being one of the few people capable >>> >of changing their mind and admitting it. (About their interpretation of >>> >what someone else meant, not the physics itself!). >>> >>> "Charge " is just a word, and words are subject to different >>> definitions by different people. I don't think many people here would >>> get the reality wrong. >>> >>> Engineers don't always use terms or methods that scientists would >>> approve of. We do what works. When we do cheat the physics, we need to >>> be careful. >>> >>> John- Hide quoted text - >>> >>> - Show quoted text - >> >> >> >>"When we do cheat the physics" ... interesting concept. >> > > Yup. We use math that doesn't actually work, but gets close enough to > do the job. We use terminology, like "charge", in our own way. We use > empirical properties of things for which we have no theory or > explanation. We do simulation and firmware where any concept of proper > dimensional analysis is totally lost... just sling the numbers around > until it works. We use proper physics when it helps, ignore it when it > doesn't. 'Fraid to say this is not true, what we use are approximations to what we *think* is the proper physics. The reality is all our physical laws cannot be proven to be correct, they only give consistent results with experiments. However, some of these laws seem to hold so universally that to challenge them would require significant experimental results to show inconsistency. We don't cheat physics, we approximate, sometimes as you say empirically when we have no model to use. > > What's interesting is that most physicists are terrible electronic > circuit designers, as their journals often show in hilarious ways. > > One example is their devoted love of jfet differential pairs when the > second fet isn't necessary and just multiplies the noise by sqrt(2). > And their abiding affection for trimpots, as opposed to proper biasing > design. > > John > > |