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From: Otto Bahn on 30 Mar 2010 14:36 <barbara(a)bookpro.com> 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. >>>> >> >>>> >> P'raps you should ask Doctroid what he is a doctroid of. >>>> >> >>>> >> BW >>>> > >>>> > See, the thing about high school physics is, it's taught by high >>>> > school >>>> > teachers out of high school textbooks to high school students. >>>> > >>>> > High school physics teachers usually do not have advanced training in >>>> > physics. Often neither do the authors of high school physics >>>> > textbooks. >>>> > Even when they do, they recognize the necessity of presenting a >>>> > simplified picture to high school students, who are not ready for >>>> > differential equations, surface integrals, and deep questions about >>>> > the >>>> > meaning of physical law. >>>> > >>>> > So what gets taught is "Ohm's law is V = IR". The ones who go on to >>>> > earn degrees in physics are taught there's more to it than that. >>>> > (And >>>> > some of them learn it.) The ones who major in English Lit or >>>> > Business >>>> > or Electrical Engineering? Might not. >>>> >>>> Since R=V/I is a definition, care to elaborate on when the relationship >>>> does not hold? >>>> >>>> Your Nobel awaits. >>> >>> I refuse to enter into further public discussion with people with no >>> reading comprehension skills. As before, you can write me at rsholmes >>> dot physics dot syr dot edu, if you are genuinely interested in >>> learning. >>> >> >>From Fundementals of Physics by Halliday and Resnick: >> >>"The relationship V = i/R remains as the derfinition of the resistance of >>a conductor whether or not the conductor obeys Ohm's law." > > So the conductor might not obey Ohm's law. Some of these mokes have > been claiming that everything always obeys Ohm's law. Just because there's a few misbehaving conductors doesn't mean the rest of us shouldn't obey Ohm's law. --oTTo--
From: Hatunen on 30 Mar 2010 14:39 On Tue, 30 Mar 2010 10:27:52 -0400, Doctroid <doctroid(a)mailinator.com> wrote: >In article <ebv3r55bt7v35nvejvpplqhr51dlpkklhi(a)4ax.com>, > barbara(a)bookpro.com wrote: > >> On Tue, 30 Mar 2010 09:29:17 -0400, "J. Clarke" >> <jclarke.usenet(a)cox.net> wrote: >> >> >On 3/30/2010 8:07 AM, Doctroid wrote: >> >> >> Anyone wishing to take this up with me further may write to me at >> >> rsholmes at physics dot syr dot edu. >> > >> >Would you be kind enough to provide us an example of the equation that V >> >and I follow for a material that does not obey ohm's law and tell us for >> >what material that equation is valid? >> >> Oopsie, looks like you posted this accidentally to Usenet. >> >> BW > >'sOK, I can take this one. > >Zener diode: > >http://www.reuk.co.uk/OtherImages/current-voltage-graph-zener-diode.gif Ther's nothing there to indicate that Ohm's Law doesn't apply to each point on the curve. In fact, this is a first year engineering problem. The resistance at any point on the curve is the inverse of the first derivative (e.g., the inverse of the slope). -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: Brian M. Scott on 30 Mar 2010 14:38 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. 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. Brian
From: Hatunen on 30 Mar 2010 14:40 On Tue, 30 Mar 2010 10:29:46 -0400, "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. -- ************* DAVE HATUNEN (hatunen(a)cox.net) ************* * Tucson Arizona, out where the cacti grow * * My typos & mispellings are intentional copyright traps *
From: jimp on 30 Mar 2010 14:40
In sci.physics Brian M. Scott <b.scott(a)csuohio.edu> wrote: > On Tue, 30 Mar 2010 17:05:07 -0000, > <jimp(a)specsol.spam.sux.com> wrote in > <news:3jn987-38o.ln1(a)mail.specsol.com> in > sci.lang,alt.religion.kibology,alt.usage.english,sci.physics: > >> In sci.physics Doctroid <doctroid(a)mailinator.com> wrote: > >>> In article <g2k987-ktn.ln1(a)mail.specsol.com>, jimp(a)specsol.spam.sux.com >>> wrote: > >>>> In sci.physics Doctroid <doctroid(a)mailinator.com> wrote: > > [...] > >>>> > So what gets taught is "Ohm's law is V = IR". The ones who go on to >>>> > earn degrees in physics are taught there's more to it than that. (And >>>> > some of them learn it.) The ones who major in English Lit or Business >>>> > or Electrical Engineering? Might not. > >>>> Since R=V/I is a definition, care to elaborate on when the relationship >>>> does not hold? > >>>> Your Nobel awaits. > >>> I refuse to enter into further public discussion with people with no >>> reading comprehension skills. As before, you can write me at rsholmes >>> dot physics dot syr dot edu, if you are genuinely interested in learning. > >> From Fundementals of Physics by Halliday and Resnick: > >> "The relationship V = i/R remains as the derfinition of >> the resistance of a conductor whether or not the >> conductor obeys Ohm's law." > > Which clearly implies that V = I/R is *not* Ohm's law -- > exactly as Doctroid said. My understanding, which could > well be wrong, is that a conductor obeys Ohm's law precisely > when a plot of V against I is linear, meaning that the > resistance, as defined by R = I/V, is a constant independent > of V and I. > > [...] > > Brian Yep, people, including me, sometimes get sloppy with language. Bottom line, the relationship V = I/R is always true for everything. For things where the plot of V = I/R results in a straight line, i.e. R is a constant, that thing obeys Ohm's law. -- Jim Pennino Remove .spam.sux to reply. |