Charge Conservation - Hint of the Day
in [Design]
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From: Jim Thompson on 20 Jul 2010 16:48 On Tue, 20 Jul 2010 17:49:28 +0100, John Devereux <john(a)devereux.me.uk> wrote: >Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> writes: > >> Charge Conservation - Hint of the Day: >> >> How many Coulombs can a 1mH inductor charged to 1A deliver? > >Hi Jim, > >I think it depends on your definitions, > >I think most would say it will start out "delivering" one Coulomb per >second, I.e. that is what flows through an external circuit. The >subsequent behaviour, and hence total number of Coulombs "delivered", >depends on what it is actually connected to. The charge delivered would >be unlimited for a superconducting shorted-out inductor, and would be >infinitesimal if the inductor was open circuited. > >But in the "all charge is conserved" picture all the charge that exits >one terminal gets returned to the other. So Zero. > >So which definition do you want to use? At least you exhibit some thought on the problem. Thanks! > >And then of course there is the secret Jim Thompson Interpretation of >Electrical Circuits... :) ...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 |
From: Jim Thompson on 20 Jul 2010 17:04 On Tue, 20 Jul 2010 08:58:13 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott <tim(a)seemywebsite.com> >wrote: > >>On 07/20/2010 08:24 AM, Jim Thompson wrote: >>> Charge Conservation - Hint of the Day: >>> >>> How many Coulombs can a 1mH inductor charged to 1A deliver? >> >>That's insufficient information, and I rather expect that you know it. > >He promised us, a couple of weeks ago, a "mathematical proof" of >something or other charge related. Is this lame snarky "hint" the best >he's been able to come up with? > >John Cluck! Cluck! Cluck! Cluck! ESAD! I may be a snarky ol' git, but I'm GOOD ;-) I'm a graphical/pictorial sort of guy... Normally I'd do this sort of thing on a white board, before an audience at one of my seminars, only an outline in front of me, then "play" the audience. So I've been struggling to create the pictorial on a series of sheets of paper to properly describe (and solve the issue). It's funny, the only time I've had time to think this through has been while sitting in doctors' waiting rooms. This morning, at Barnet-Dulaney (wife's eyes, YAG lasers, cataracts), I fitted the pictorial together in my head. Within the next 48 hours you, John "The Bloviator" Larkin (and ALL your supplicants) are going to be BURNED AT THE STAKE... One-by-one every one of your STUPID STUPID STUPID statements will be refuted (message ID's supplied to prove you made the STUPID STUPID STUPID statements). I'm working now on how to distribute the material so that it can't be disseminated, so that everyone can have a good laugh... BEHIND YOUR WORTHLESS BACK ;-) RECANT! RECANT! THE END IS NEAR :-) ...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 |
From: Richard Henry on 20 Jul 2010 19:25 On Jul 20, 2:04 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- Web-Site.com> wrote: > On Tue, 20 Jul 2010 08:58:13 -0700, John Larkin > > > > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott <t...(a)seemywebsite.com> > >wrote: > > >>On 07/20/2010 08:24 AM, Jim Thompson wrote: > >>> Charge Conservation - Hint of the Day: > > >>> How many Coulombs can a 1mH inductor charged to 1A deliver? > > >>That's insufficient information, and I rather expect that you know it. > > >He promised us, a couple of weeks ago, a "mathematical proof" of > >something or other charge related. Is this lame snarky "hint" the best > >he's been able to come up with? > > >John > > Cluck! Cluck! Cluck! Cluck! ESAD! > > I may be a snarky ol' git, but I'm GOOD ;-) > > I'm a graphical/pictorial sort of guy... > > Normally I'd do this sort of thing on a white board, before an > audience at one of my seminars, only an outline in front of me, then > "play" the audience. > > So I've been struggling to create the pictorial on a series of sheets > of paper to properly describe (and solve the issue). > > It's funny, the only time I've had time to think this through has been > while sitting in doctors' waiting rooms. This morning, at > Barnet-Dulaney (wife's eyes, YAG lasers, cataracts), I fitted the > pictorial together in my head. > > Within the next 48 hours you, John "The Bloviator" Larkin (and ALL > your supplicants) are going to be BURNED AT THE STAKE... > > One-by-one every one of your STUPID STUPID STUPID statements will be > refuted (message ID's supplied to prove you made the STUPID STUPID > STUPID statements). > > I'm working now on how to distribute the material so that it can't be > disseminated, so that everyone can have a good laugh... BEHIND YOUR > WORTHLESS BACK ;-) > > RECANT! RECANT! THE END IS NEAR :-) > Is this the way your seminars end?
From: Tim Wescott on 20 Jul 2010 20:32 On 07/20/2010 09:32 AM, Jim Thompson wrote: > On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott<tim(a)seemywebsite.com> > wrote: > >> On 07/20/2010 08:24 AM, Jim Thompson wrote: >>> Charge Conservation - Hint of the Day: >>> >>> How many Coulombs can a 1mH inductor charged to 1A deliver? >> >> That's insufficient information, and I rather expect that you know it. > > No. It's provided to cause young bucks to do some thinking. Looks > like it didn't work with you :-( > > (Except that it did annoy Larkin, yet again... so a partial success > :-) Since you didn't answer I have to assume that you couldn't. Either this is a trick question, and the answer is "however many excess electrons it has sitting on it when I hand it to you", or the answer is "that depends on the coil resistance". A 1mH superconducting inductor with 1A will deliver (or flow, if you want to quibble about the common EE definition of "deliver") an infinite charge to a dead short, assuming all conductors are also zero resistance. Otherwise a 1mH inductor that sees R ohms of total circuit resistance in the inductor and the load (charge target?) will see it's current decay as (1A)*e^-(R/L)*t; this will integrate to (1A) * (L/R). So for 1 ohm total resistance that'd be 1mC, for a 10 ohm total resistance that'd be 100uC, for a 0.1 ohm total resistance it'd be 10mC, etc. Answers involving loads that aren't purely resistive are more complicated, but still obvious if you can understand the above. But to answer how much charge that 1mH inductor _can possibly_ deliver when it has 1A flowing through it depends on the particular inductor's winding resistance and possibly also on whether it's really a 1mH inductor when it has 1A flowing through it. You may want to pop over to the closest ASU campus that presents EEE 202 and see if you can audit the course. This problem is no great mystery for someone who's gotten through sophomore electronics engineering. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: John Fields on 20 Jul 2010 20:36
On Tue, 20 Jul 2010 08:24:26 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >Charge Conservation - Hint of the Day: > >How many Coulombs can a 1mH inductor charged to 1A deliver? --- Well, let's see... Since the collapsing magnetic field around an ideal one henry inductor with one ampere of current in it will deliver about 6.24e18 electrons into any load when its current source is abruptly terminated, a one millihenry coil, under the same conditions, should deliver about about three orders of magnitude less, about one millicoulomb. JF |