Peter T. Daniels ran out of electrical outlets; states rewiring entire house to be the only feasible solution.
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From: Otto Bahn on 31 Mar 2010 11:42 "PaulJK" <paul.kriha(a)paradise.net.nz> 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. >> >> Water, per se, is a pretty good insulator. > > Well, the flesh and blood will supply some salts and other > chemicals which should make the moisture more conductive. > > What is most unfortunate is that the nerves are extra > good conductors. Of course it's their purpose in life to > conduct el-chem signals. Anybody here study bio-electricity? I did. Nerves don't obey ohm's law. The propagation of a signal down a nerve is very complicated -- a partial differential equation over both time and distance. One of the many variables is the migration of ions through the cell membrane. --oTTo--
From: Otto Bahn on 31 Mar 2010 11:43 "PaulJK" <paul.kriha(a)paradise.net.nz> 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. The red one's I popped most definitely had a visible gap inside the plastic and did not conduct electricity. --oTTo--
From: Evan Kirshenbaum on 31 Mar 2010 11:46 Peter Moylan <gro.nalyomp(a)retep> writes: > Evan Kirshenbaum wrote: >> Hatunen <hatunen(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. I know. It's the one I used as a high school senior in 1981[1] (although it was "Halliday and Resnick" back then). It's also the source of one of the longest strings of prepositional phrases that's evern brought itselft to my attention. From memory (after all these years): The force exerted by the rope on one side of a point in the rope on the rope on the other side of the point is called the _tension_ at that point. > 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.) [1] I'm pretty sure. Either that or it was the other one I used when studying for the AP exam. -- Evan Kirshenbaum +------------------------------------ HP Laboratories |Usenet is like Tetris for people 1501 Page Mill Road, 1U, MS 1141 |who still remember how to read. Palo Alto, CA 94304 kirshenbaum(a)hpl.hp.com (650)857-7572 http://www.kirshenbaum.net/
From: Otto Bahn on 31 Mar 2010 11:47 "Adam Funk" <a24061(a)ducksburg.com> wrote >>>>> It's true that a great many resistors are nearly linear, i.e. they can >>>>> be said to obey Ohm's law to a reasonable degree of accuracy, provided >>>>> that you don't go beyond their design limits. >>> >>>Well, another way to look at it is that the resistance changes in >>>various situations, such as, erm, higher voltages. >> >> The most familiar example is the common incandescent lamp, which >> has a low resistance when first turned on. See >> http://www.sylvaniaautocatalog.com/sylvania/imgs/resistance_vs_temp.gif > > AIUI, this is part of the reason (the low initial resistance > aggravates the thermal shock) that lamps generally blow when switched > on from cold --- right? Yup. If you always warm up you light bulbs before turning them on, they last longer, but it's cheaper just to buy a new bulb now and then. --oTTo--
From: Hatunen on 31 Mar 2010 12:42
On Tue, 30 Mar 2010 21:22:50 -0500, Al in St. Lou <alfargnoli(a)yahoo.com> wrote: >On Tue, 30 Mar 2010 14:52:26 -0700, Hatunen <hatunen(a)cox.net> wrote: > >>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.... > >You're forgetting his earlier post where he burnt it out: "...increase >the voltage until it goes 'Pop.'" No. But I took that to be metaphorical for the point at which the diode becomes conductive and the current abruptly rises. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps * |