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From: Mike Barnes on 31 Mar 2010 03:17 Hatunen <hatunen(a)cox.net>: >Current and voltage are not arbitrary but are well defined in >terms other than V = IR. This makes resistance the derived >quantity with no circularity involved save for the kid in the >back of the classroom who won't accept the teacher's explanation >and keeps picking arguments. If that was aimed at me (and it might have been, or it might not have been), I'll remark that when I was questioning whether one quantity was derived from another, neither of them was resistance. I remember being the kid at the *front* of the class, and I was very quiet. -- Mike Barnes Cheshire, England
From: Mike Barnes on 31 Mar 2010 03:36 Peter Moylan <gro.nalyomp(a)retep.?.invalid>: >jimp(a)specsol.spam.sux.com wrote: >> In sci.physics "Peter Duncanson (BrE)" <mail(a)peterduncanson.net> wrote: > >>> If a closed circuit, a resistive ring for instance, is put in a varying >>> magnetic field an induced current will flow but no potential difference >>> will be created. >> >> True if, and only if, the "resistive" ring is an ideal superconductor >> with zero resistivity, otherwise there will be a potential difference >> between any two given points on the ring. >> >Oops, I've just sent a response to this before realising that the >response was going to sci.physics alone. That means that some of the >participants in this discussion, including me, won't see it. That nearly happened to me a few times. But my software refuses to post a message which wouldn't go to any newsgroup I'm subscribed to: the message just sits there in my Outbox. So I notice that it hasn't gone and reinstate the original groups (to Laura's disappointment, I'm sure). -- Mike Barnes Cheshire, England
From: Otto Bahn on 31 Mar 2010 11:25 "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.... There is now -- POP goes the weasle. --oTTo--
From: Otto Bahn on 31 Mar 2010 11:27 "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. --oTTo--
From: Otto Bahn on 31 Mar 2010 11:37
"PaulJK" <paul.kriha(a)paradise.net.nz> wrote i >>>>>>>>> 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. > > But it applies even to the conductor of Boston Philharmonic. If you are altnernating the conductors, then you have to call it impedence. --oTTo-- |