Haveing a material that's 'ohmic' is not what the law is about.
Here is a very simple illustration:
Take a regualted, adjustable power supply and connect a variable resistor.
Set up the power supply for constant volts.
Vary and volts and observe the current meter varying with the voltage.
Vary the resistance and observe the current meter varying inversly with resistance.
Ohm's law holds for both cases, hence Voltage, Current and Resistance are variables.
Now, set up the source for constant current.
Vary the current and observe voltage changes with current.
Vary the resistance and observe voltage changes with resistance (proportionally)
Ohm's law holds for all cases, hence Voltage, Current and Resistance are all variables.
You're not stuck with it. You're putting unnessary restrictions on the law. The law holds for the general case of variable resistance, as well as for the speicific case you want to badly to ram home.
"ohmic" referes to a material that behaves as in your simple, special case. However, the law holds for non-ohmic materials as well.
Tesla23:
What happens is some people learn the law by looking at V=I*R or similar, and never get the real truth behind the experiment that led to the result of proportionality. They are given the math first rather than the experiment first.
Please see the above 6 steps of Ohm's Law and see what you think about that.
I am an Engineer. No, not all the Universities teach that R cannot vary. It's typical to teach a simple version of a physical law in the introductory courses, something that my Physics professor would rage over. What do you mean I won't listen to anyone else? Lots of people agree with my I've written on both of the threads that deal with this matter. Just because I know someting doesnt' mean I don't listen. You have a way of making statements about things you don't know about.
Look I'm just happy that no-one is objecting to the statement:
1. in most homogeneous materials (i.e. no junctions), for all practical purposes V = IR where R is a function of temperature only
This is what Ohm was first to discover and what we use all the time, every time we use a resistor in a potential divider, to sense current, to calculate I^2R losses etc...
You won't change the world. If the only exposure many folk have had to Ohm's law is in circuit theory then I can see why they think that it is a fundamental relationship between V, I and R and is not related to physics (even though they assert it is a physical law). I think that they then get themselves into a little trouble when they state things like an IN914 diode with V=0.5V has a resistance of 5kΩ and then at 0.7V has a resistance of 140Ω (computed from the datasheet), when if they said that anywhere else no-one would have any idea what they were talking about.
I honestly don't have any idea what is going on in this thread, but if you are trying to tell us that resistance can never change, I have a surprise for you.R is a CONSTANT.
Are you perhaps saying that we have to resort to the total underlying physics to explain the difference between r and R?
You cant possibly be an EE and not know what an ohmic device is
vs a non ohmic device.
So name me one simple ohmic device that exists and name me one simple
non ohmic device. Dont cop out this time, name two devices in real
life that exist and can be discussed.
I can see you just like arguing so if you decide not to name two devices
this time i wont continue talking to you.
I suggest that we start pointing to established definitions, such as "ohmic" and "non-ohmic" if that hasn't already been done. Likewise, definitions of parameter/variable, and constant or any other relevant mathematical terms.
Dont ask BrownOut for an ohmic device though,
he might bring you a 1N4148 diode! ha ha
I am an EE, with a degree and everything. You make too many ASS-umptions about what I do and don't know. This discussion was not about my knowledge of what an ohmic device is or isn't; it was about whether or not R is a constant. You made as ASSumption about the extent of my knowledge, and BTW you got it WRONG! Just as pretty much every thing else you got wrong.
Also, I'm not your effing student, so you don't get to test my knowledge. Besides, I've already answered more of your irrelavnat and trivial questions than I ever care to answer. I don't feel like wasting any more of my time on someone who will just pretend I've refused to answer questions that I've clearly given my answer to. It's clear to me by now that you have nothing else of value to add to the discussion, and you're now just using obfuscation and distortion with all you're spurrious charges about questions, question, questions... You're not going to be satisfied no matter how many of your questions get answered, and will always have more qustions, so you can pretend that someone isn't responding correctly. Well, nobody cares what you think a correct response it. I know I know what I know, so you can take your dime-store quzzes and stuff then somewhere, I care not where.
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