tom: in response to your rhetorical question ... (1) as you well know, an ohm's law device is one in which current is proportional to voltage: I = V/R. double the voltage and the current doubles; halve the voltage and the current drops to half; reverse the voltage and the current changes sign. an ordinary copper wire is a good example of a practical ohm's law device. (2) a diode does not obey ohm's law. in particular, reverse the voltage on an initially forward biased diode and the current stops. (3) perhaps in the experiment you alluded to current was measured for a number of different voltages, and effective resistances were computed by dividing voltage by current for each V,I combination - is it possible that it was these computed resistances that fit accepted resistance values to an accuracey of 1%? surely the diode didn't agree with ohm's law to within 1%. (4) simply diving voltage by current to compute resistance is not an application of ohm's law. ohm's law is very special, and when a device obeys ohm's law, it really means that R = constant and the current follows the straight line relationship, I =V/R. a good analogy might be that we wouldn't say that a parabala was a straight line because we could compute the slope of the tangent line at every point on the curve. (5) no device obeys ohm's law exactly, and ohm's law fails for all devices at sufficiently high voltages. dlk
On Fri, 14 Nov 2003 17:01:32 -0600, tom ring <taring@TARING.ORG> wrote: >Hmm, despite the "failure" of ohms law, we were able to use it in my 500 level >(that would be graduate level to non engineers) radio frequency non-linear >transistor design course, we were still able to get answers better that 1 >percent accurate. Guess we were just lucky. > >I'm done with this topic on the list. Let's take it offline folks. |
Please note - During the past 17 years of operation, several gigabytes of
Vanagon mail messages have been archived. Searching the entire collection
will take up to five minutes to complete. Please be patient!
Return to the archives @ gerry.vanagon.com
The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.
Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.