Peter T. Daniels ran out of electrical outlets; states rewiring entire house to be the only feasible solution.
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From: jimp on 29 Mar 2010 20:59 Peter Moylan <gro.nalyomp(a)retep> wrote: > jimp(a)specsol.spam.sux.com wrote: >> In sci.physics Doctroid <doctroid(a)mailinator.com> wrote: >>> In article <nq6787-qkc.ln1(a)mail.specsol.com>, jimp(a)specsol.spam.sux.com >>> wrote: >>> >>>> All things obey Ohm's law exactly because R=V/I is the definition of >>>> resistance. >>> In that case I hereby announce Doctroid's Law which states that >>> >>> V = D * C >>> >>> where V is the electrical potential across a device, and C is the total >>> mass of chocolate consumed in the past year by the person who measures >>> V. D is the device's Doctroidance, which is in fact defined by D = V / >>> C, and of course is not constant. Therefore Doctroid's law always holds >>> for all circumstances. >>> >>> It is also perfectly useless. As is Ohm's Law, if you consider it to be >>> solely a definition of resistance: it has no predictive power. >> >> Sorry, the universe, empirical data, and better than a century of electrical >> engineering and physics disagree with your conclusion. >> >> And obviously the phrase "characteristic curve" is meaningless to you. >> > On the contrary, Doctroid has captured the essential point. Ohm's law is > useful for linear resistors. For nonlinear resistors, you can if you > wish *define* resistance as the ratio of voltage to current, but doing > so leads you into a fairly pointless side track. > > People who work with nonlinear electrical circuits do find it useful, > often, to define a thing called incremental resistance, but that concept > is useful only if the conditions are such that it makes sense to > linearise the circuit equations around an operating point. People that work with electrical circuits, linear or otherwise, find it useful to understand what the phrases characteristic curve, load line, and operating point mean, all of which are nothing more than a graphical representation of Ohms law. > Let me restate Ohm's law. "Ohm's law says that Ohm's Law may be applied > to all devices that obey Ohm's Law, but not otherwise." R=V/I is the definition of resistance at any point in time or under any operating condition for anything with an applied voltage and a current flow. > Skitt did bring up a valid point with respect to tissue damage. In that > case you can consider the affected tissue to have a resistance that has > (irreversibly) changed as a function of the amount of damage done. Muddled right out of the starting gate. In dealing with a bulk material, such as skin, resistivity is the characteristic of interest. Skin resistivity will change reversibly for a number of reasons, and even if damaged, there is a process called "healing". > That's not quite the same thing as a resistance that is a function of > applied voltage. In this case you have a phenomenon that can be broken > down into three time intervals. > 1. Initially, you have a constant resistance, and Ohm's law applies. Ohm's law always applies, even for things with strange characteristic curves like Esaki diodes. > 2. Then there's a complicated nonlinear process where energy is causing > tissue damage, and the current varies with time even if the applied > voltage remains constant. In this phase, Ohm's law is useless. Nope, you just plot a characteristic curve over time, and the energy causing damage isn't electrical, it is thermal. > 3. Eventually you will probably get a steady state in which the > resistance as again constant, although not the same constant as in phase 1. Nope, keep going and the tissue will go through dehydration, carbonization, and eventually combustion until all you have is ash. -- Jim Pennino Remove .spam.sux to reply.
From: PaulJK on 30 Mar 2010 01:40 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. Oh, dear, dear, you couldn't be more wrong if you tried real hard. :-) > 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...) M'lord, how is this meaningless babbling relevant to our case at hand? pjk > Dave
From: David DeLaney on 29 Mar 2010 19:40 Otto Bahn <Ladybrrane(a)GroinToHell.com> wrote: >"Adam Funk" <a24061(a)ducksburg.com> wrote >>> If that is so, then please tell me how you define "resistance". >> >> It's futile, Doctroid. > >What's impeding it? Mental megaohms. ("How many? What does the meter say?") IT'S OVAR NIEN THOUSAAAAAND! Dave -- \/David DeLaney posting from dbd(a)vic.com "It's not the pot that grows the flower It's not the clock that slows the hour The definition's plain for anyone to see Love is all it takes to make a family" - R&P. VISUALIZE HAPPYNET VRbeable<BLINK> http://www.vic.com/~dbd/ - net.legends FAQ & Magic / I WUV you in all CAPS! --K.
From: PaulJK on 30 Mar 2010 01:57 Peter Moylan wrote: > PaulJK wrote: >> Doctroid wrote: >>> In article <homphq$91l$1(a)news.eternal-september.org>, >>> "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. >> > Except when it isn't - which is most of the time. > > 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. > > It's equally true that some resistive devices are *deliberately* made to > be nonlinear. A semiconductor diode, for example, would be totally > useless if it obeyed Ohm's law. I see you didn't have Ohm's law in your high school? What has nonlinearity to do with it? Absolutely nothing. At every point in time and at every point inside the body of a resistive conductor the Ohm's law applies with 100% accuracy. It is applicable even when the conductors are never completely homogeneous and never absolutely linear. (Excepting conditions in the super conductive environment.) pjk
From: PaulJK on 30 Mar 2010 01:59
Mike Barnes wrote: > jimp(a)specsol.spam.sux.com: >> In sci.physics Mike Barnes <mikebarnes(a)bluebottle.com> wrote: >>> Hatunen <hatunen(a)cox.net>: >>>> On Sat, 27 Mar 2010 09:29:58 +0000, Mike Barnes >>>> <mikebarnes(a)bluebottle.com> wrote: >>>> >>>>> Hatunen <hatunen(a)cox.net>: >>>>>> On Fri, 26 Mar 2010 08:06:21 +0000, Jonathan de Boyne Pollard >>>>>> <J.deBoynePollard-newsgroups(a)NTLWorld.COM> wrote: >>>>>>> [...] >>>>>>> energy being delivered, the amount of which is >>>>>>> determined by the wattage, >>>>>> >>>>>> I suppose one might casually say that, but in fact the power >>>>>> (wattage) is a function of the current and resistance, not >>>>>> vise-versa. >>>>> >>>>> How so? >>>> >>>> Power is a result of passing a current through a resistance; >>>> current and rsistance aren't a result of power. >>> >>> But it seems to me equally valid to say that current is the result of >>> generating power in a resistance. You can't pass current without >>> generating power, and you can't generate power without passing current. >>> They are two sides of the same of coin. It seems wrong to me to insist >>> (as you seemed to be doing) that one is the cause of the other. >>> >>> [X-posting to sci.physics with some trepidation] >>> >> >> A resistance can not generate power, it can only dissipate it. What about a bunch of black shirt anarchists? :-) > You won't find me disagreeing with that (but I don't see the relevance). > >> The power dissipated in a resistance is a function of the resistance and >> the externally generated voltage applied to the resistance. > > Ditto. |