Peter T. Daniels ran out of electrical outlets; states rewiring entire house to be the only feasible solution.
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From: Hatunen on 30 Mar 2010 17:51 I make no assumptions about where the people reading this are, but I don't subscribe to sci.physics so I'm restoring the original list of newsgroups. Elsewise even I wouldn't be able to read my message without subscribing and I really don't want to subscribe to sci.physics. On Tue, 30 Mar 2010 17:53:51 -0000, jimp(a)specsol.spam.sux.com wrote: >In sci.physics Hatunen <hatunen(a)cox.net> wrote: >> On Sun, 28 Mar 2010 20:18:39 -0400, dbd(a)gatekeeper.vic.com (David >> DeLaney) wrote: >> >>>PaulJK <paul.kriha(a)paradise.net.nz> wrote: >>>>Doctroid wrote: >>>>> "PaulJK" <paul.kriha(a)paradise.net.nz> wrote: >>>>>> Voltage and current are proportional to each other. >>>>>> It is therefore sufficient to say that damage is proportional >>>>>> to one of them. >>>>> >>>>> Only in materials and voltage/current ranges where Ohm's "law" is >>>>> obeyed. And if damage is occurring, it probably isn't. >>>> >>>>Ohm's law is always obeyed in all aparatus made by humans. >>> >>>... ... Okay, so you're not an engineer AND are not an experimentalist. >>>Meaning you're a theorist. This explains some things. >>> >>>(Tell the court, please, how long ago it was that humans made the first >>>material that had exactly the same resistance at every interior point, and >>>how to get current to go through an object in such a way as to have the same >>>current density everywhere inside the object...) >> >> As taught in high school science classes, Ohm's Law is the >> familiar V = IR. but in the real world Ohm's Law is valid for all >> kinds of cases of non-constant factors, writte in lower case, v = >> ir to indicate the values are non-constant. In gneral, Ohm's law >> is expressed e = iz, where, as I note in another post, z is >> impedance, which can be resistive or reactive and therefore >> contain an imaginary component, and e is the term usually used >> for "voltage". In fact, in the generic case the for Ohm's Law is >> a differential equation with time dependency. >> >> Obviously, some cases will be intractable to solution, but the >> fact that we can't solve it doesn't mean Ohm's Law doesn't remain >> true; there are approximation methods that can yield useful >> results. And, yes, Ohm's law is applicable to bulk materials as >> well as the idealized linear forms. >> >> This is all quite practical and not theoretical out in the real >> world. There are qutie a few eingineers that cope with this sort >> of stuff on a daily basis. >> >> In other word, Ohm's Law is always true and you should avoid >> making such statements unless you know what you're talking about. > >Ohm's law is not V = IR, but rather deals with the special case of V = IR >where the R is constant as in a metallic conductor. Gee. Why didn't I think of that? Oh, that's right; I did and said so way back there in the subthreads. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Hatunen on 30 Mar 2010 17:52 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.... -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Hatunen on 30 Mar 2010 17:57 On Tue, 30 Mar 2010 14:38:32 -0400, "Brian M. Scott" <b.scott(a)csuohio.edu> 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: this clearly means >that they don't obey Ohm's law as Doctroid (and, I might >add, Halliday & Resnick) use the term. I quote H&R (1967): > > A conductor obeys Ohm's law only if its V-I curve is > linear, that is, if R is independent of V and I. The > relationship R = V/I remains as the general definition of > the resistance of a conductor whether or not the > conductor obeys Ohm's law. > >Even my old text, Kingsbury (1965), which isn't nearly so >good as H&R, says the same thing: > > Thus one may say that [V = IR] is a defining equation > for resistance, R, and that Ohm's law is a statement > that resistance is independent of the magnitude of the > current. Ohm's law is thus similar to Hooke's law in > that it is valid for certain materials under certain > limited conditions. Hooke's law is the basis of all elasticity effects, and like Ohm's Law can be applied to bulk materials. The fact that you have to use the calculus to describe it doesn't alter that fact. I'm beginning to think that engineers know things that physics professors and authors don't. >From a more recent text, Paul A. Tipler, _Physics for >Scientists and Engineers_: > > Ohm's law is not a fundamental law of nature, like > Newton's laws or the laws of thermodynamics, but > rather an empirical description of a property shared > by many materials. Quite. And I doubt it would be called a "law" if Ohm had come up with it today. Even Newton's Laws are no longer considered laws. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Hatunen on 30 Mar 2010 17:59 On Tue, 30 Mar 2010 10:12:26 -0400, dbd(a)gatekeeper.vic.com (David DeLaney) wrote: >Hatunen <hatunen(a)cox.net> wrote: >>"Otto Bahn" <Ladybrrane(a)GroinToHell.com> 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. > >Clearly, more research is required. I have here a quantity of chicken legs, >frankfurters, and scuba divers... If I'm the one grilling those chicken legs on the barby I reckon you'll have lots of specimens.. You can have the skin and I'll take the legs. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Hatunen on 30 Mar 2010 18:00
On Tue, 30 Mar 2010 15:46:32 -0400, "Otto Bahn" <Ladybrrane(a)GroinToHell.com> 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. Water, per se, is a pretty good insulator. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps * |