- #36
Kholdstare
- 388
- 1
Nevertamed said:
You got me wrong there. I said,
I = [itex]\frac{V}{R(V)}[/itex]
But,
[itex]\frac{I_{2}}{I_{1}}[/itex] [itex]\neq[/itex] [itex]\frac{V_{2}}{V_{1}}[/itex]
Nevertamed said:dude could u explain wtf are u talking about? under that condition voltage follows current proportionally: CORRECT
I= V R: WRONG
vk6kro said:You actually said that
Given a constant temperature current will be equal to voltage multiplied by resistance. - correct
and this is totally wrong.
And this one is correct although you feel it is wrong:
Given a constant temperature current will be proportional to voltage. - wrong
This is a practical subject and nobody cares if a wire has a resistance of 100 ohms or 100.001 ohms.
jim hardy said:i'm real simple. sometimes to the point it bothers folks, but here's my two cents:
an ohm is what a volt will push an amp through.
that's proportionality
and there's no temperature in that.
if some piece of real world conductor is one ohm at , say the ice point,
and you change its temperature
it won't be one ohm anymore
and a different voltage will be necessary to push one amp through it.
that's still proportionality.
don't complicate what is simple.
maybe you are confused by ohm's thermocouple source which is a strong function of temperature. that's part of the applied voltage, not the resistance.
keep the change --
old jim
Kholdstare said:@nevertamed - I'm very sorry that my first post had the mistake I = VR. What I actually meant is clarified in my third post.
@vk6kro - I was just saying that even in constant temperature QM effects will very the resistance depending on bias. Of course it is convenient to tolerate this variation and use Ohm's law in large conductors in practice. But that does not alter the fact that QM effect gives a more accurate description of I-V than Ohm's law does.
Kholdstare said:@nevertamed - I'm very sorry that my first post had the mistake I = VR. What I actually meant is clarified in my third post.
@vk6kro - I was just saying that even in constant temperature QM effects will very the resistance depending on bias. Of course it is convenient to tolerate this variation and use Ohm's law in large conductors in practice. But that does not alter the fact that QM effect gives a more accurate description of I-V than Ohm's law does.
In its most general form, the Ohm has nothing to do with materials and everything to do with the scalar ratio of Electric to Magnetic fields over suitable line integrals.
The propagation of energy in free space takes place at 376.7 Ohms.
All material characterizations are specific cases of this general definition.
sophiecentaur said:I don't understand what people are wanting out of this thread. Do they want to prove it 'wrong' or something?
You're right!Macroscopic or QM - it's all a matter of 'horses for courses'.
Whilst one might well use QM to design a circuit component, one would never design a whole circuit using more than Ohm's law.
That's exactly what I'm trying to do.I don't understand what people are wanting out of this thread. Do they want to prove it 'wrong' or something?
Even in case of large materials QM description gives much better accuracy than Ohm's law.It's no more than an equation that operates over the linear regime. The fab thing about metals is just how wide that regime happens to be.
I appreciate that he really did very well to propose the law at that time. But when a more accurate law comes out it replaces the old one. Just like general relativity replaced Newton's law of gravity.I think George did very well, all those years ago, to get it down on paper. Just think of the muddled thinking that used to be applied to Science in those days. (And, even today, on some of these threads!)
jim hardy said:rigo.altervista.org/papers/engineering_procedure.pdf
Saying that you don't understand it. Meaning "I don't believe it, it's too crazy, it's the kind of thing I just ... I'm not going to accept."
Eh. The other part well... this kind, I hope you'll come along with me. "I don't have to accept it". Because it's the way nature works. If you want to know the way nature works, we looked at it, carefully, ... that's the way it works.
You don't like it..., go somewhere else!
To another universe! Where the rules are simpler, philosophically more pleasing, more psychologically easy. I can't help it! OK! If I'm going to tell you honestly what the world looks like to the... human beings who have struggled as hard as they can to understand it, I can only tell you what it looks like.
And I cannot make it any simpler, I'm not going to do this, I'm not going to simplify it, and I'm not going to fake it. I'm not going to tell you it's something like a ball bearing inside a spring, it isn't.
So I'm going to tell you what it really is like, and if you don't like it, that's too bad.
Read not to contradict and confute, nor to believe and take for granted... but to weigh and consider.
there are several possible levels of treatment and this has surely led to some confusion here.
jim hardy said:i don't deal with anything smaller than surface mount resistors.
QM is outside my experience.
consider another proportionality
Rate = Distance/Time
As a member of 'unwashed masses' i won't embrace QM unless it'll get me out of a speeding ticket.
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if i offended anyone please accept this apology.
I'm sorry. But when someone asks me limit of something I usually look for the validity of that thing in more difficult levels where it might fail. If we only considered the easier levels we would not be looking for its 'limits'. Would we?there are several possible levels of treatment and this has surely led to some confusion here.
There is contradiction. The application of macroscopic and QM approach on same structure gives different results.There is no essential contradiction in the Macroscopic and QM approaches but I think some of the contributors are glorying in the prospect of there being some conflict. A very counter - productive attitude.
jim hardy said:might this QM effect be at all related to the observable physical phenomenon of "noise" generated by resistors? Carbon I'm told is worst and wirewound the best..