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From: Hatunen on 31 Mar 2010 12:44 On Wed, 31 Mar 2010 17:32:24 +1200, "PaulJK" <paul.kriha(a)paradise.net.nz> wrote: >Hatunen wrote: >> There's no gap in a semiconductor diode.... > >You can view the P-N junction as a kind of an equivalent of >a gap. "Kind of equivalent"? Now there's a precise technical term. >It also breaks catastrophically when certain voltage >is reached. Almost everything will break catastrophically when a certain voltage is reached. I should think we are dealing in operation within the stated safe parameters here. > -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Hatunen on 31 Mar 2010 12:47 On Wed, 31 Mar 2010 11:27:44 -0400, "Otto Bahn" <Ladybrrane(a)GroinToHell.com> wrote: >"Hatunen" <hatunen(a)cox.net> wrote in > >>>>>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. >> >> Water, per se, is a pretty good insulator. > >If you were that low on electrolytes, you'd already be dead. Read again. The subject at hand is the charred area. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Hatunen on 31 Mar 2010 12:49 On Wed, 31 Mar 2010 20:35:01 +1100, Peter Moylan <gro.nalyomp(a)retep> wrote: >Evan Kirshenbaum wrote: >Evan, you have grasped the essence far more quickly than those who claim >to have read Resnick and Halliday. > >(That's a very old introductory physics textbook, in case you don't >know. It's so old that I used it myself as a first-year student. When I was a demonstrator at McGill University 1965-66 that was the text in use for first year students. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Jerry Friedman on 31 Mar 2010 13:08 [I decided this one wasn't interesting to a.r.k., based partly on a comment by a kibologist.] On Mar 31, 3:35 am, Peter Moylan <gro.nalyomp(a)retep> wrote: > Evan Kirshenbaum wrote: > > Hatunen <hatu...(a)cox.net> writes: > > >> I prefer not to use dictionaries for definitions of technical and > >> scientific terms. > > >> Wikipedia is closer: > > >> "In electrical circuits, Ohm's law states that the current through a > >> conductor between two POINTS is directly proportional to the > >> potential difference or voltage across the two POINTS, and inversely > >> proportional to the resistance between them, provided that the > >> temperature remains constant."[Emphasis added] > > >>http://en.wikipedia.org/wiki/Ohm%27s_law > > >> Note that this definition does not require the points to be > >> external. > > > But it does require that the current and voltage between the points be > > "directly proportional". To me, that means that there is some > > *constant* of proportionality, and that if one doubles, the other will > > necessarily double. I realize that my grounding in physics is much > > less than many here, but I had thought that that was precisely the > > point of contention here. > > Evan, you have grasped the essence far more quickly than those who claim > to have read Resnick and Halliday. > > (That's a very old introductory physics textbook, in case you don't > know. It's so old that I used it myself as a first-year student. Like > any first-year text, it doesn't go into the details that an advanced > text will cover. It does, IIRC, point out that - by definition - only > linear devices obey Ohm's law, a detail that some people appear to have > bleeped over.) I'm about to teach a class based on the eighth edition, of 2008. (Today we're going to do multiloop circuits with more than one voltage source.) The name in biggest type on the cover is that of Jearl Walker, a colleague of Brian Scott's, whose _Scientific American_ columns many here will remember. This edition defines the resistance as V/i and says, "*Ohm's law* is an assertion that the current through a device is _always_ directly proportional to the potential difference applied to the device. (This assertion is correct only in certain situations; still, for historical reasons, the term 'law' is used.)... A conducting device obeys Ohm's law when the resistance of the device is independent of the magnitude and polarity of the applied potential difference." I rather like that, though maybe it would be useful in some situations to define R as dV/di. (The ninth edition is coming out right about now.) -- Jerry Friedman
From: ke10 on 31 Mar 2010 13:11
In article <houmt9$sj7$2(a)news.eternal-september.org>, PaulJK <paul.kriha(a)paradise.net.nz> wrote: >Brian M. Scott wrote: >> >> 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) I've been waiting for someone to say what Brian has just said. You were taught to use a particular expression to mean X; others were taught (by equally reputable authorities) to use it to mean Y. Maybe you could all live with it, rather than squabbling about each other's qualifications in physics? Now one party or the other could say "but definition X is more *useful* than definition Y, because it makes certain discussions clearer". That would be a tenable view, but asserting that either definition is fundamentally wrong is about as much use as disputing about angels on the head of a pin. Katy |