A resistor has an identical resistance value for both DC and AC voltages (disregarding real world parasitics). Simple as that.
An incandescent light bulb is a temperature dependent resistor, but the temperature rise is identical for DC and the same AC RMS voltage.
Another way of viewing it: a resistor has unity power factor.
A diode or LED doesn’t have those properties.
I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).
But a lot of people have trouble in recognizing that.
I just wanted to see how widespread this misconception is.
For example, in this other forum (or whatever it is called) it was argued that you can't use a multimeter measure the resistance of an LED because "it is not a resistor", while in fact the incapability to return a value is that at the small testing current used by the DMM either the voltage had to exceed the compliance of the current source, or the resistance to measure would be out of range.
You don't even follow your own rules. A DMM does measure the "resistance" of a diode, including Leads AT THE OPERATING POINT DEFINED BY THE DMM'S DESIGN.. No confusing nonsense about compliance points etc.
This is why the definition of resistance you propose is not particularly useful.
Can you show that an LED does not have unity power factor?
Another way of viewing it: a resistor has unity power factor.
A diode or LED doesn’t have those properties.
Can you show that an LED does not have unity power factor?
I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).
You could distinguish between resistors and nonresistors just based on your stated criteria, but then neither actual resistors nor LEDs would qualify since their previous history determines their thermal profile (temperature and internal gradients) and probably other things--thus their states are not determined solely by present values.
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But a lot of people have trouble in recognizing that.
I just wanted to see how widespread this misconception is.
Some ways of understanding things are more useful than others. I think most of us understand the operation of an LED well enough to fully utilize and accomodate its characteristics without classifying it as a non-linear resistor. Can you explain how considering it a non-linear resistor is helpful?
This is a misunderstanding of the nature of the component and of the operation of the DMM.
I am a black swan hunter, and misconceptions like these are the main food of black swans.
All these times, I thought resisters are those who fight against the enemy while under enemy occupation....
Precision use of language has it minuses. I think those trained in engineering or physical sciences have a tendency to demand the same precision in wording from others. This may be why in most businesses-side folks and tech-side folks don't communicate well with "the other side".
I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.
It reminds me of that chapter in "Are you joking Mr. Feynman ?" when Feynman was in Brazil and found that physics education there was fundamentally notionistic.
The diode-resistor issue seems to point to a compartmentalized knowledge problem, where the student is not able to generalize a concept learned in a previous chapter (or course) because nobody has connected the dots for him/her.
I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.
Can you show that an LED does not have unity power factor?
I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.
Could you be less grandiose and more specific?
its more like an antenna
A resistor is a circuit component with the primary purpose of acting as a resistor. A diode (LED or otherwise) is not such a component.
-snip-
What I might grant you, is the often stated idea that a diode can magically drop 0.6 V in a circuit. What can be missed about this is the fact that the diode will necessarily dissipate heat equal to 0.6 V times the current flowing. The voltage drop is not "magic", it is resistive in nature.
But a diode does act as a resistor: a giant (almost independent from operating point) resistance that impede current flow when reverse biased, and a small (operating point dependent) resistance that let current flow when forward biased. And you confirm it in your last paragraph.
It walks like a duck, it quacks like a duck and it dissipates power like a duck.
I assure you, this is not a troll post.
From the point of view of circuit theory, a diode IS a nonlinear resistor. Period.
You can read, for example, Chua, Desoer and Kuh, "Linear and nonlinear circuits". Top level authors and respected university level textbook.
I did, in the post you are quoting.
The inability to generalize a concept, namely the concept that resistors are described by voltage-current characteristics that do not need to be linear (nor symmetric).
I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.
The diode-resistor issue seems to point to a compartmentalized knowledge problem, where the student is not able to generalize a concept learned in a previous chapter (or course) because nobody has connected the dots for him/her.
"Aren't all memoryless, time-invariant two-ports just voltage dependent resistors in the end?"
- Gustav Kirchhoff, probably
I am (mostly) fine with the generalization. In fact it seems I did guess what this was all about after all (if jokingly):"Aren't all memoryless, time-invariant two-ports just voltage dependent resistors in the end?"
- Gustav Kirchhoff, probably
What is a very bad idea in my opinion is implicitly broadening the meaning of a word. You are effectively redefining the word "resistor" to encompass this generalization.