Ohm's Law Problem
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From: Spehro Pefhany on 15 Feb 2010 17:36 On Mon, 15 Feb 2010 14:06:41 -0800, the renowned life imitates life <pasticcio(a)thebarattheendoftheuniverse.org> wrote: >On Mon, 15 Feb 2010 16:38:42 -0500, Spehro Pefhany ><speffSNIP(a)interlogDOTyou.knowwhat> wrote: > >>On Mon, 15 Feb 2010 12:24:59 -0800, the renowned life imitates life >><pasticcio(a)thebarattheendoftheuniverse.org> wrote: >> >>>On Mon, 15 Feb 2010 10:49:56 -0500, Spehro Pefhany >>><speffSNIP(a)interlogDOTyou.knowwhat> wrote: >>> >>>>On Mon, 15 Feb 2010 07:22:37 -0800, the renowned life imitates life >>>><pasticcio(a)thebarattheendoftheuniverse.org> wrote: >>>> >>>>>On Mon, 15 Feb 2010 09:46:23 -0500, Spehro Pefhany >>>>><speffSNIP(a)interlogDOTyou.knowwhat> wrote: >>>>> >>>>>>On Mon, 15 Feb 2010 06:35:19 -0500, the renowned Rich Webb >>>>>><bbew.ar(a)mapson.nozirev.ten> wrote: >>>>>> >>>>>>>On Mon, 15 Feb 2010 00:48:46 -0500, Spehro Pefhany >>>>>>><speffSNIP(a)interlogDOTyou.knowwhat> wrote: >>>>>>> >>>>>>>>On Sun, 14 Feb 2010 16:12:04 -0800 (PST), the renowned Bill Bowden >>>>>>>><wrongaddress(a)att.net> wrote: >>>>>>>> >>>>>>>>>Ohm's Law Problem: >>>>>>>>> >>>>>>>>> Find the voltage at the 2 junctions of a 3 element voltage >>>>>>>>> divider across a supply voltage of 8.4 volts. The two >>>>>>>>> junctions of the divider both supply external current of 5mA. >>>>>>>>> >>>>>>>>> V1 +8.4 >>>>>>>>> | >>>>>>>>> R1 = 240 >>>>>>>>> | >>>>>>>>> V2 .---------> 5 mA >>>>>>>>> | >>>>>>>>> R2 = 570 >>>>>>>>> | >>>>>>>>> V3 .---------> 5 mA >>>>>>>>> | >>>>>>>>> R3 = 100 >>>>>>>>> | >>>>>>>>> | >>>>>>>>> GND >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>(V1-V2)/R1 = 5mA + (V2-V3/R2 >>>>>>>>(V2-V3)/R2 = 5mA + V3/R3 >>>>>>>> >>>>>>>>V1 is known (8.40V), so this is 2 equations in two unknowns and easily >>>>>>>>solved for V2 = 5.169230769 V, V3=0.346153846 V. >>>>>>> >>>>>>>The Curse of the Calculator strikes again! >>>>>>> >>>>>>>I3 = 3.5 mA, V3 = 0.35 V, and V2 = 5.2 V. Hard to justify more than two >>>>>>>significant figures here. >>>>>> >>>>>>Hey there, we wouldn't want some question of the correct value of the >>>>>>NINETH digit on the 'ol Agilent 3458A, now would we.. ;-) >>>>>> >>>>>> >>>>>> >>>>>>Best regards, >>>>>>Spehro Pefhany >>>>> >>>>> >>>>> Nineth? >>>>> >>>>> Doth thee haveth a nineth digit? >>>> >>>>Well, eight and a half, so not directly applicable in this particular >>>>case, but it's not totally ridiculous calculating DC voltages to 10 or >>>>11 places when such tools are at hand. Certainly to 7 places. >>>> >>>> >>>>Best regards, >>>>Spehro Pefhany >>> >>> >>> The word is Ninth. And no, that meter doesn't have that many either. >> >>http://www.eefocus.com/data/myspace/3/17997//blog/2a65afe9.jpg >> > > It is an 8 and a half digit meter. Sure, that's why it takes nine digits to express the reading. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Joerg on 15 Feb 2010 17:34 Jim Thompson wrote: > On Mon, 15 Feb 2010 13:29:30 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> Joel Koltner wrote: >>> "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in >>> message news:11sin51vdubl64ouhcgn3b2omf36q111in(a)4ax.com... >>>> Everyone is making it too difficult. Just write it down in sequence, >>>> the answer falls right out... >>>> http://analog-innovations.com/SED/OhmsLaw_SED_JustWriteItDown.pdf >> Ohm's law? I thought that had been repealed ... :-) >> >> >>> That's the same as what I ended up doing (in the later part of my post), >>> except that you use "V3/100" rather than just "I" for the current in the >>> lowest resistor. :-) >>> >>>> At MIT, I was spared (*) from Guillemin's obtuseness, I had Harry B. >>>> Lee for passive circuit analysis ;-) >>> I had a guy who was a pretty talented teacher (he'd won a couple awards >>> for it, and I found him quite understandable), although he had little if >>> any real-world design experience. >>> >>> I'd read some of Guillemin's book, and while I think the guy was pretty >>> darned sharp, I disagree with his notion that you have to have an >>> incredibly thorough understanding of network analysis down pat before >>> you can get useful circuit design or analysis done. ... >> >> Sadly, that's the kind of notion that drives potential EE candidates >> away, at least from analog. And now we have a serious shortage of those. >> They think they have to be a rocket scientists to be able to thrive and >> make money in analog. Which is wrong. I learned the majority of my >> skills by "winging it". IOW I built RF stuff before I knew squat about >> any of that. And it actually worked, some still does. >> >> Note to potential candidates: If an author or professor says something >> like what must have been stipulated in this book, that you must be a top >> notch network analyst, do not listen. It's much more important to >> experiment, experiment, experiment, get a "feel" for what works, _then_ >> dive into the theory. Not the other way around. Just my 2 cents. >> >> Whew. Now I feel better ... > > I always vote for too few analog engineers ;-) > No, not good. It hurts our economy and there comes a day when you and I and the other guys are pushing daisies. And then? > Virtually everything I attack, I have no initial clue about how to > make it work. That's what makes it fun ;-) > Same here. Like an injector thingie last year. Works :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 15 Feb 2010 17:57 On Mon, 15 Feb 2010 14:34:56 -0800, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Mon, 15 Feb 2010 13:29:30 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Joel Koltner wrote: >>>> "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in >>>> message news:11sin51vdubl64ouhcgn3b2omf36q111in(a)4ax.com... >>>>> Everyone is making it too difficult. Just write it down in sequence, >>>>> the answer falls right out... >>>>> http://analog-innovations.com/SED/OhmsLaw_SED_JustWriteItDown.pdf >>> Ohm's law? I thought that had been repealed ... :-) >>> >>> >>>> That's the same as what I ended up doing (in the later part of my post), >>>> except that you use "V3/100" rather than just "I" for the current in the >>>> lowest resistor. :-) >>>> >>>>> At MIT, I was spared (*) from Guillemin's obtuseness, I had Harry B. >>>>> Lee for passive circuit analysis ;-) >>>> I had a guy who was a pretty talented teacher (he'd won a couple awards >>>> for it, and I found him quite understandable), although he had little if >>>> any real-world design experience. >>>> >>>> I'd read some of Guillemin's book, and while I think the guy was pretty >>>> darned sharp, I disagree with his notion that you have to have an >>>> incredibly thorough understanding of network analysis down pat before >>>> you can get useful circuit design or analysis done. ... >>> >>> Sadly, that's the kind of notion that drives potential EE candidates >>> away, at least from analog. And now we have a serious shortage of those. >>> They think they have to be a rocket scientists to be able to thrive and >>> make money in analog. Which is wrong. I learned the majority of my >>> skills by "winging it". IOW I built RF stuff before I knew squat about >>> any of that. And it actually worked, some still does. >>> >>> Note to potential candidates: If an author or professor says something >>> like what must have been stipulated in this book, that you must be a top >>> notch network analyst, do not listen. It's much more important to >>> experiment, experiment, experiment, get a "feel" for what works, _then_ >>> dive into the theory. Not the other way around. Just my 2 cents. >>> >>> Whew. Now I feel better ... >> >> I always vote for too few analog engineers ;-) >> > >No, not good. It hurts our economy and there comes a day when you and I >and the other guys are pushing daisies. And then? We will be a watermelon-dominated society, so who will care ?:-) > > >> Virtually everything I attack, I have no initial clue about how to >> make it work. That's what makes it fun ;-) >> > >Same here. Like an injector thingie last year. Works :-) (:-0) ...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 | I love to cook with wine. Sometimes I even put it in the food.
From: life imitates life on 15 Feb 2010 18:02 On Mon, 15 Feb 2010 17:36:09 -0500, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Mon, 15 Feb 2010 14:06:41 -0800, the renowned life imitates life ><pasticcio(a)thebarattheendoftheuniverse.org> wrote: > >>On Mon, 15 Feb 2010 16:38:42 -0500, Spehro Pefhany >><speffSNIP(a)interlogDOTyou.knowwhat> wrote: >> >>>On Mon, 15 Feb 2010 12:24:59 -0800, the renowned life imitates life >>><pasticcio(a)thebarattheendoftheuniverse.org> wrote: >>> >>>>On Mon, 15 Feb 2010 10:49:56 -0500, Spehro Pefhany >>>><speffSNIP(a)interlogDOTyou.knowwhat> wrote: >>>> >>>>>On Mon, 15 Feb 2010 07:22:37 -0800, the renowned life imitates life >>>>><pasticcio(a)thebarattheendoftheuniverse.org> wrote: >>>>> >>>>>>On Mon, 15 Feb 2010 09:46:23 -0500, Spehro Pefhany >>>>>><speffSNIP(a)interlogDOTyou.knowwhat> wrote: >>>>>> >>>>>>>On Mon, 15 Feb 2010 06:35:19 -0500, the renowned Rich Webb >>>>>>><bbew.ar(a)mapson.nozirev.ten> wrote: >>>>>>> >>>>>>>>On Mon, 15 Feb 2010 00:48:46 -0500, Spehro Pefhany >>>>>>>><speffSNIP(a)interlogDOTyou.knowwhat> wrote: >>>>>>>> >>>>>>>>>On Sun, 14 Feb 2010 16:12:04 -0800 (PST), the renowned Bill Bowden >>>>>>>>><wrongaddress(a)att.net> wrote: >>>>>>>>> >>>>>>>>>>Ohm's Law Problem: >>>>>>>>>> >>>>>>>>>> Find the voltage at the 2 junctions of a 3 element voltage >>>>>>>>>> divider across a supply voltage of 8.4 volts. The two >>>>>>>>>> junctions of the divider both supply external current of 5mA. >>>>>>>>>> >>>>>>>>>> V1 +8.4 >>>>>>>>>> | >>>>>>>>>> R1 = 240 >>>>>>>>>> | >>>>>>>>>> V2 .---------> 5 mA >>>>>>>>>> | >>>>>>>>>> R2 = 570 >>>>>>>>>> | >>>>>>>>>> V3 .---------> 5 mA >>>>>>>>>> | >>>>>>>>>> R3 = 100 >>>>>>>>>> | >>>>>>>>>> | >>>>>>>>>> GND >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>(V1-V2)/R1 = 5mA + (V2-V3/R2 >>>>>>>>>(V2-V3)/R2 = 5mA + V3/R3 >>>>>>>>> >>>>>>>>>V1 is known (8.40V), so this is 2 equations in two unknowns and easily >>>>>>>>>solved for V2 = 5.169230769 V, V3=0.346153846 V. >>>>>>>> >>>>>>>>The Curse of the Calculator strikes again! >>>>>>>> >>>>>>>>I3 = 3.5 mA, V3 = 0.35 V, and V2 = 5.2 V. Hard to justify more than two >>>>>>>>significant figures here. >>>>>>> >>>>>>>Hey there, we wouldn't want some question of the correct value of the >>>>>>>NINETH digit on the 'ol Agilent 3458A, now would we.. ;-) >>>>>>> >>>>>>> >>>>>>> >>>>>>>Best regards, >>>>>>>Spehro Pefhany >>>>>> >>>>>> >>>>>> Nineth? >>>>>> >>>>>> Doth thee haveth a nineth digit? >>>>> >>>>>Well, eight and a half, so not directly applicable in this particular >>>>>case, but it's not totally ridiculous calculating DC voltages to 10 or >>>>>11 places when such tools are at hand. Certainly to 7 places. >>>>> >>>>> >>>>>Best regards, >>>>>Spehro Pefhany >>>> >>>> >>>> The word is Ninth. And no, that meter doesn't have that many either. >>> >>>http://www.eefocus.com/data/myspace/3/17997//blog/2a65afe9.jpg >>> >> >> It is an 8 and a half digit meter. > >Sure, that's why it takes nine digits to express the reading. > > >Best regards, >Spehro Pefhany The only two values the first digit can have with the others filled up is zero or one. That is only half a digit in meter speak. I'll leave it to you, this time around, to figure out the simple reason why.
From: Fred Bartoli on 15 Feb 2010 18:16
Joerg a �crit : > Jim Thompson wrote: >> On Mon, 15 Feb 2010 13:29:30 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Joel Koltner wrote: >>>> "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> >>>> wrote in message news:11sin51vdubl64ouhcgn3b2omf36q111in(a)4ax.com... >>>>> Everyone is making it too difficult. Just write it down in sequence, >>>>> the answer falls right out... >>>>> http://analog-innovations.com/SED/OhmsLaw_SED_JustWriteItDown.pdf >>> Ohm's law? I thought that had been repealed ... :-) >>> >>> >>>> That's the same as what I ended up doing (in the later part of my >>>> post), except that you use "V3/100" rather than just "I" for the >>>> current in the lowest resistor. :-) >>>> >>>>> At MIT, I was spared (*) from Guillemin's obtuseness, I had Harry B. >>>>> Lee for passive circuit analysis ;-) >>>> I had a guy who was a pretty talented teacher (he'd won a couple >>>> awards for it, and I found him quite understandable), although he >>>> had little if any real-world design experience. >>>> >>>> I'd read some of Guillemin's book, and while I think the guy was >>>> pretty darned sharp, I disagree with his notion that you have to >>>> have an incredibly thorough understanding of network analysis down >>>> pat before you can get useful circuit design or analysis done. ... >>> >>> Sadly, that's the kind of notion that drives potential EE candidates >>> away, at least from analog. And now we have a serious shortage of >>> those. They think they have to be a rocket scientists to be able to >>> thrive and make money in analog. Which is wrong. I learned the >>> majority of my skills by "winging it". IOW I built RF stuff before I >>> knew squat about any of that. And it actually worked, some still does. >>> >>> Note to potential candidates: If an author or professor says >>> something like what must have been stipulated in this book, that you >>> must be a top notch network analyst, do not listen. It's much more >>> important to experiment, experiment, experiment, get a "feel" for >>> what works, _then_ dive into the theory. Not the other way around. >>> Just my 2 cents. >>> >>> Whew. Now I feel better ... >> >> I always vote for too few analog engineers ;-) >> > > No, not good. It hurts our economy and there comes a day when you and I > and the other guys are pushing daisies. And then? > > >> Virtually everything I attack, I have no initial clue about how to >> make it work. That's what makes it fun ;-) >> > > Same here. Like an injector thingie last year. Works :-) > Same. I always tell my prospects/customers that, not knowing it's impossible, I've way more chances than the previous half baked attempts... -- Thanks, Fred. |