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Do you think an LED is a resistor?

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Sredni:

--- Quote from: bdunham7 on April 24, 2024, 04:27:20 pm ---
--- Quote from: Sredni on April 24, 2024, 04:04:03 pm ---A bald man is a man.
A one-legged man is still a man, even if in all medicine books the body of a man is shown with two legs.

--- End quote ---
How about a fictional man?  Or a robotic man?  An AI man?  A virtual man? 

--- End quote ---

Seriously?
Is a non-car a car?
Is a carrot a car?

We are at this point?
If you had read any of the circuit theory or general engineering books I have given you would know that in order to be part of the set --- let's call "all resistor" the elements need to share a common trait. Like when in that video for kids you have all vegetables in one set and all fruits in another set (and don't bring out the tomato!).

So, what is the common trait shared by the elements of the set "all resistors"? It's that they are fully characterized by a relationship between voltage and current. Only between V and I. Not q and V (those are capacitors) and not phi and I (those are inductors).

So, "all resistors" have a characteristic that is implicitly defined by  f(v, I)=0, that is a curve in the vi plane.

Now, among all these resistors, some have a curve that is a straight line, that is a v + b I = 0, which you can rewrite as v = R I. This is the subset "linear resistors" of the set "all resistors". It is a very important set because it has all the easy to understand properties of linear functions, including superposition. That is why we strive to make our components the more linear possible (yes, the five striped thingies called "resistors" you can buy are actually nonlinear and can only be considered linear within specified limits). Since they are so easy to understand, we teach about them in high school and we simply call them "resistors" not to overload feeble minds with unnecessary complications
 
But the set "(linear) resistors" is not the entire set "all resistors". We are left with all those components that are described by a VI characteristic that is NOT linear, like diodes, scrs, mov, incandescent lamps, neon bulbs... These form the huge subset "nonlinear resistors" of the larger set "all resistors". So, they are resistors with f(v,I) nonlinear.

And no, a carrot is not a car.

bd139:
You sound like a programmer. Only programmers fuck up taxonomies this badly.

Simon:
As predicted you started a stupid poll to piss everyone off by changing the question. Why don't you go back to those other forums where got your stupid little smartarse question. Come back when you have grown up!

EEVblog:

--- Quote from: Sredni on April 21, 2024, 02:47:14 pm ---
--- Quote from: switchabl on April 21, 2024, 01:54:31 pm ---Is this one of those trick questions where you pull a small-signal model out of your hat when everyone's distracted or explain later that when you said "resistor" you didn't actually mean resistor?

--- End quote ---

No, no trick question at all.
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.

A diode is a resistor in the same way an incandescent lamp is a resistor. Both are nonlinear and both have exponential V-I characteristics. And yet everyone has no problem in computing power dissipated in circuits with incandescent lamp treating them as resistors, while when it comes to diodes the 'hard' exponential seems to create a mental block.

I just wanted to see how widespread this misconception is.

--- End quote ---

I've seen it taught that as a non-linear resistor for the purposes of calcuation, but it's not a resistor, it's a diode. Try changing the polarity and see what happens.
By your standard diodes are also resistors, or the B-E junction of a transistor is also a resistor, which is silly.

Simon:
Dave, I locked the thread and this guy is taking the piss. PM from him:


--- Quote ---Hi, have you had a breach in the system?
In the poll "do you think an LED is a resistor?" You wrote that the question was changed.

I just checked and the question is as I first formulated it. Has it been changed by someone else and then reverted back to its original form?

--- End quote ---

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