Peter T. Daniels ran out of electrical outlets; states rewiring entire house to be the only feasible solution.
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From: PaulJK on 31 Mar 2010 02:05 Evan Kirshenbaum wrote: > Hatunen <hatunen(a)cox.net> writes: > >> On Tue, 30 Mar 2010 14:11:42 -0400, "Otto Bahn" >> <Ladybrrane(a)GroinToHell.com> wrote: >> >>> "Hatunen" <hatunen(a)cox.net> wrote >>> >>>>>>> Resistance is the opposition offered by a body or substance to >>>>>>> the passage through it of an electric current. >>>>>> >>>>>> Quantitative definition, please, not just a description. Here >>>>>> is a 1N4002 diode: How would you determine its resistance? >>>>> >>>>> Slowly increase the voltage across it until it goes "pop". >>>>> It's resistance is now pretty much infinite for any value >>>>> of voltage you're likely to apply. >>>> >>>> "Pretty much infinite". Is that an engineering term? >>> >>> Yes, when we don't feel like calculating at what voltage arcing >>> across the gap might occur. >> >> There's no gap in a semiconductor diode.... > > Even after it's gone "pop"? No, there's usually no gap. The semiconductor diods I used to torture to death usually exhibited near zero resistance in both directions after they've gone "pop". Of course the "pop" was usually accompanied by a more spectacular and loud "kha-boom" from the nearby fuses. If a more powerful power source was used the diods often tried to escape it by performing a quick transition of their solid bodies to a white hot liquid form and dripping all over my shoes. pjk
From: Jerry Friedman on 31 Mar 2010 01:12 On Mar 30, 4:25 pm, Hatunen <hatu...(a)cox.net> wrote: > On Tue, 30 Mar 2010 14:59:19 -0700 (PDT), Jerry Friedman > > > > <jerry_fried...(a)yahoo.com> wrote: > >On Mar 30, 3:54 pm, Hatunen <hatu...(a)cox.net> wrote: > >> On Tue, 30 Mar 2010 11:17:42 -0700 (PDT), Jerry Friedman > > >> <jerry_fried...(a)yahoo.com> wrote: > >> >On Mar 29, 12:52 pm, "Skitt" <skit...(a)comcast.net> wrote: > >... > > >> >> Ohm's Law does not provide a "quantitative definition". As I said, it > >> >> describes a relationship. When values of two of the variables are provided, > >> >> the value of the third can be obtained. > > >> >I'd have said that Ohm's Law /is/ the quantitative definition of > >> >resistance. For objects in which current is proportional to voltage > >> >(with other things, such as the temperature, held fixed), the > >> >resistance between two given points (I should have said) > >> >is V/I. For others, such as diodes, the resistance can't > >> >be defined. > > >> But it's done all the time, nevertheless. It has to be treated > >> infinitesimally, though, with calculus. > > >People define resistance as the slope of the V-versus-I curve? What > >for, situations where you're going to be changing voltage only > >slightly and you want to approximate the diode as a resistor? > > If you want to approximate the diode as a resistoyou measure the > current at full forward and revers voltage and get the on-off > resistances. That means the on resistance and the off resistance? > Very few applications rquire the maintaining of a > diode at voltages at some midpoint. Anyway, this is interesting. My experience with diodes is negligible. -- Jerry Friedman
From: PaulJK on 31 Mar 2010 02:14 Peter Moylan wrote: > PaulJK wrote: > >> A homework for Doctroid and P.Moylan >> http://www.allaboutcircuits.com/worksheets/diode1.html >> >> just trying to help you to stop embarrassing yourself with >> high school physics. > > If we're exchanging web links, here's one for you. > > http://www.pmoylan.org/pages/research/publ-circuits.html Oh humpty doo. You want me to recite to you at which university I got my degrees in el.engineering and on which universities and faculties I lectured with list of my publications to see if it's longer than yours? My link was to the point. pjk
From: PaulJK on 31 Mar 2010 02:38 Brian M. Scott wrote: > On Wed, 31 Mar 2010 17:24:00 +1200, PaulJK > <paul.kriha(a)paradise.net.nz> wrote in > <news:houigv$gc9$1(a)news.eternal-september.org> in > sci.lang,alt.religion.kibology,alt.usage.english,sci.physics: >> Brian M. Scott wrote: >>> On Wed, 31 Mar 2010 04:57:47 +1200, PaulJK >>> <paul.kriha(a)paradise.net.nz> wrote in >>> <news:hot6pr$fal$1(a)news.eternal-september.org> in >>> sci.lang,alt.religion.kibology,alt.usage.english,sci.physics: >>>> J. Clarke wrote: >>>>> On 3/30/2010 10:27 AM, Doctroid wrote: > >>> [...] > >>>>>> Zener diode: > >>>>>> http://www.reuk.co.uk/OtherImages/current-voltage-graph-zener-diode.gif > >>>> Well? The semiconductors exhibit highly nonlinear >>>> relationship between voltage and their resistance >>>> resulting in nonlinear relationship between voltage and >>>> the current. > >>> It seems to me that you (and several others) aren't paying >>> attention to what Doctroid is saying: > >> No sorry, Brian, I believe we do pay sufficient attention. >> The thing is that what he and the below quoted "authorities" >> say about applicability of Ohm's law is to us a load of crock. > >> The linearity of V-I curve has absolutely nothing to do >> with validity of Ohm's law. > > You're still not paying attention: in their framework this > linearity *is* Ohm's law, Yes, Brian, I well understand their point of view. The disagreement is indeed as you say about what meaning should be assigned to the term 'Ohm's law'. What I (and some others in this thread) were taught was that Ohm's law was V=IR. (fullstop) No linearity is implied. It is equally applicable in conductors with variable non-linear resistance/reactance and equally applies in complex high frequency environments. It is obeyed and applicable everywhere in nature even in complex non-linear environments, like brain and nerves or in lightnings. I don't know if this was the way the law was understood by Ohm in its year naught, but that was the modern version of the law I was taught and used in differential equations, Laplace and Z transforms describing the behaviour of the el.circuits. The reason for my disagreeing with "them" is not for the lack of attention, we simply disagree on that fundamental level of what is and isn't Ohm's law. pjk > so in that framework it's absurd > to say that it has nothing to do with the validity of Ohm's > law. In particular, when the term 'x satisfies Ohm's law' > means that the V-I curve for x is linear, then it is > perfectly true that not all materials are ohmic (follow > Ohm's law). > > So far as I can tell, you and these authorities -- and scare > quotes are *not* appropriate here -- do not disagree on the > physical facts; you merely mean different things by the term > 'Ohm's law'. If you're going to argue, you should at least > argue over the actual point of difference, namely, what > meaning should be assigned to the term 'Ohm's law'. > > [...] > > Brian
From: PaulJK on 31 Mar 2010 02:42
Peter Moylan wrote: > Otto Bahn wrote: >> "Hatunen" <hatunen(a)cox.net> wrote >> >>>> Out of curiosity, is the resistance of charred skin the same as >>>> the resistance of normal skin? >>> If it's charred I would imagine it's lower. >> >> I'd guess the absence of water would make it go up. > > I've never measured it, but my guess is the same as yours. >> >> More Resistance! > > Resistance is futile. HA! But I know how to use my towel... pjk |