| Electronics > Beginners |
| how exactly resistor works |
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| westfw:
Going back to the original question... In an ideal conductor, you could sort-of think of an electron going in one end with a particular energy, and coming out the other end with exactly the same energy. In a real conductor, things in the conductor interfere with the passage - in particular it interacts with the electrons that are already in the atoms that make up conductor (and probably the nuclei as well) - and it ends up spending some of its energy making those move around on a molecular and atomic level (ie, generates heat.) (it's one of the things that makes superconductors so amazing - how can you possibly move electronics through a medium without having them interact with anything?) The same thing happens with water in a pipe - some of the kinetic energy of the individual water molecules gets wasted interacting with the walls of the tube, bumping into each other, and so on. |
| Brumby:
Getting back to the original question is exactly what should happen more often in the Beginners section. To the OP, the departures from what may be helpful to you in this thread are not new or something special thrown down to scare you off. It happens all too frequently. So much so, this little graphic needs to be flown every now and then.... |
| T3sl4co1l:
Another classic symptom: once the original question is answered satisfactorily, thread drift and quibble is inevitable. It is up to the reader to decide when the thread has lost its value. Yet another skill, but this time at least it's generally applicable to all parts of life, including IRL conversations, Facebook comments and so on. If the answer is not satisfactory to the OP, but OP does not respond in a timely manner to notify of that fact -- and give additional information with which to formulate a more appropriate answer -- replies will default to their own assumptions, and the above happens regardless. You have a duty, as the question-asker, to steer conversation in a useful direction. If you just leave it alone, what do you expect is going to happen? :-// Most of all, this is a free forum, it's not like you've paid anyone to furnish an answer on a silver plate. ;D (Which, if you have a few bucks to spare, I'm sure many would work with you for a very good answer. Tutoring isn't free!) Tim |
| Bassman59:
--- Quote from: imo on September 29, 2018, 06:02:28 pm ---Btw, a typical standard Q during exams from "Theory of Electromagnetic fields" subject the EE students usually get is to derive the Ohm's law from the Maxwell's equations. --- End quote --- I remember doing that, not as an undergrad, but in a graduate course in Microwave Electronics, which was really about Maxwell's Equations. And when the professor mentioned that you could derive Ohm's Law from Maxwell's Equations, it was a revelation. In all of this discussion about whether Ohm's Law is really a law or just an observation, there's a parallel in Newton's Laws of Motion. They were derived from observation and the model works extraordinarily well. So well, in fact, that they're called a Law. But they are simplifications of a more-general and more difficult physics. |
| IanB:
I believe that Ohm's Law is a property of materials. And so to derive Ohm's Law from Maxwell's equations you would have to extend those equations to include parameters that describe properties of bulk materials. Wouldn't that make the derivation a circular argument? |
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