Misconceptions and flaws noticed by the more educated...

[LvW]

..........
2) Ohm's law wrongly taught as R=E/I. R=E/I is the definition of resistance, not Ohm's law. A resistance follows Ohm's law if its value is constant over a reasonable current range. In other words, if its resistance is linear. This is expounded in physics books written by Halliday & Resnick, and Raymond Serway. A tungsten wire follows Ohm's law. A semiconductor junction does not.
.......

In this context:
Misinterpretation of the expression R=V/I: A rewriting in the form V=I*R is often used to say: A current I produces a voltage drop V across a resistor R.
Yes , it is true that we can use this relation during circuit analyses - however, physically spoken, such an interpretation is wrong.
A current canot producea voltage.
It is always a voltage, that is needed to drive a current.

 

[Akanimo]

Hi,



What do you mean by that? I just don't understand and would like to.

There are usually not enough details in so-called 'definitions'. I need detail when you are telling me about something.

Do not teach me if you do not know it. I get very bored merely seeing or hearing the phrase "it is defined as..."

 

[Ratch]

@Ratch

"2) Ohm's law wrongly taught as R=E/I. R=E/I is the definition of resistance, not Ohm's law. A resistance follows Ohm's law if its value is constant over a reasonable current range. In other words, if its resistance is linear. This is expounded in physics books written by Halliday & Resnick, and Raymond Serway. A tungsten wire follows Ohm's law. A semiconductor junction does not."

this is an issue of understanding the words

R = E/I is always true.
Ohmic devices - things that have E/I = constant over a large range of E and I, and if you reverse polarity have the same constant, and if E = 0, then I = 0 and visa-versa, like resistors, obey ohms law

non-ohmic devises, such as a semiconductor junction, have a dynamic resistance
R still = E/I, but R changes along the curve
these do not obey ohm's law, but you can still talk about the equivalent resistance at a point along the curve

"Silly Science: I will list subjects that I think are out of bounds. Anyone can present a argument why it is feasible. I will give a counter argument.

1) Climate change

2) Evolution"

does this mean you would argue for climate change and evolution, or against climate change and evolution?
and what do you mean by out of bounds?

@BradtheRad
i have never seen either of those machines
i'll have to build one or both
thanks

It would be nice if you separated my post in quote shading followed by your replies so readers can better follow the dialog.

Ohm's law is a law and a definition is a definition. For instance, velocity is defined as distance divided by time. It is always correct, yet we don't call it something like "Newton's law", do we? Same with the definition of resistance. Ohm's law pertains to the resistive linearity of a substance, not its actual resistance value. It is not a question of the meaning of words.

I miswrote about climate change. I should have said that man induced climate climate change is a myth. The climate is always changing naturally.

To clarify my view about evolution, I believe it is silly science. I am willing to argue that point.

Ratch

 

[KlausST]

Hi,

A current canot producea voltage.

A current I produces a voltage drop V across a resistor R.

I don´t see this contradictory.
The voltage(source) is produced elsewhere ... but a "drop" is at the resistor.

It´s clear: Without voltage source there will be no voltage across the resistor. (and no current either)

******
Similar with a hydraulic system.
There needs to be a pump (voltage source)
generating pressure (voltage)
this may (or may not) oil flow (current)
when oil flows there will be some resistance (hose, valve...)
and one will see a difference pressure (voltage drop) across any resistance.

No pump, no pressure, no oil flow --> difference pressure.

Klaus

 

[Ratch]

Hi,




I don´t see this contradictory.
The voltage(source) is produced elsewhere ... but a "drop" is at the resistor.

It´s clear: Without voltage source there will be no voltage across the resistor. (and no current either)

******
Similar with a hydraulic system.
There needs to be a pump (voltage source)
generating pressure (voltage)
this may (or may not) oil flow (current)
when oil flows there will be some resistance (hose, valve...)
and one will see a difference pressure (voltage drop) across any resistance.

No pump, no pressure, no oil flow --> difference pressure.

Klaus

A current has to have a voltage associated with it to pass through a resistance.

Ratch

 

[KlausST]

Hi,

A current has to have a voltage associated with it to pass through a resistance.

I already agreed with this.

Klaus

 

[d123]

Hi,

Not interested in a tiresome, politely middle-class, passive-aggressive I'm right-you're wrong tennis match with words that you enjoy so much, but I must call you out on:

I should have said that man induced climate climate change is a myth. The climate is always changing naturally.

Go into a room with 2 fully-closed windows and close the door. There is a 5mm gap under the door that leads to the outside world. Now turn on a machine or three that generate heat: maybe you will turn on the TV, the Ok Goggle or Hate Alexa machine, plug in a fridge/freezer, turn on the washing machine for an hour, heat some food in a microwave oven. Does the room heat up? Who caused that heating up of the room to occur - you or the climate changing naturally? What does mass industry, electrical infrastructure supplying homes and businesses, hydropower stations that are well-documented to warm the water where they are located, etc. around the world do: cool the planet down or heat it up? Devil's advocate to be difficult over serious matters is silly, and I'll bet you know so. I'm stupid/thick but even I can understand what we are doing. Both what happens naturally and human actions induce changes in climate, otherwise concept of cause and effect is meaningless. Kind of like saying: I just hit my head with a hammer, but it's not my fault, in fact it was the gravity of Planet Earth that is responsible for the terrible pain I feel right now??!

To clarify my view about evolution, I believe it is silly science. I am willing to argue that point.

Characters like Zlarti Bartfast aren't real, and discussing personal opinions of evolution has nothing to do with improving electronics textbooks, anyway. Also, to slightly paraphrase what they say in a certain country: It's easy to be a bullfighter sitting in the seats at the back of the arena, unless, of course, you're also an expert on that subject and right fiull stop and everyone else who works in that field is wrong...

BTW: While I may appreciate your erudition and apparently vast intelligence, I won't answer even if you deign to retort as you just seem to want to argue the toss with people to get your kicks, perhaps not always purposefully pedantic, mate. It's supposed to be about helping, not talking down to everyone from Mount Zeus. And BTW, I'm interpreting you are actually a nice, thoughtful person in person.

 

[Ratch]

Hi,

Not interested in a tiresome, politely middle-class, passive-aggressive I'm right-you're wrong tennis match with words that you enjoy so much, but I must call you out on:



Go into a room with 2 fully-closed windows and close the door. There is a 5mm gap under the door that leads to the outside world. Now turn on a machine or three that generate heat: maybe you will turn on the TV, the Ok Goggle or Hate Alexa machine, plug in a fridge/freezer, turn on the washing machine for an hour, heat some food in a microwave oven. Does the room heat up? Who caused that heating up of the room to occur - you or the climate changing naturally? What does mass industry, electrical infrastructure supplying homes and businesses, hydropower stations that are well-documented to warm the water where they are located, etc. around the world do: cool the planet down or heat it up? Devil's advocate to be difficult over serious matters is silly, and I'll bet you know so. I'm stupid/thick but even I can understand what we are doing. Both what happens naturally and human actions induce changes in climate, otherwise concept of cause and effect is meaningless. Kind of like saying: I just hit my head with a hammer, but it's not my fault, in fact it was the gravity of Planet Earth that is responsible for the terrible pain I feel right now??!

I am thinking of many centuries of yesteryear when a heavy ice sheath covered most of the northern hemisphere and eventually disappeared due to natural global warming. It did so without heavy industrial participation. What evidence can you present that shows mankind has contributed to the rise in the Earth's temperature?

Characters like Zlarti Bartfast aren't real, and discussing personal opinions of evolution has nothing to do with improving electronics textbooks, anyway. Also, to slightly paraphrase what they say in a certain country: It's easy to be a bullfighter sitting in the seats at the back of the arena, unless, of course, you're also an expert on that subject and right fiull stop and everyone else who works in that field is wrong...

I have no idea to whom you are referring, but I will say that whoever espouses evolution is wrong because evolution's premise is wrong.

BTW: While I may appreciate your erudition and apparently vast intelligence, I won't answer even if you deign to retort as you just seem to want to argue the toss with people to get your kicks, perhaps not always purposefully pedantic, mate. It's supposed to be about helping, not talking down to everyone from Mount Zeus. And BTW, I'm interpreting you are actually a nice, thoughtful person in person.

Why thank you. I believe correcting people from their wrong beliefs is a noble enterprise.

Ratch

 

[d123]

Hi,

I am thinking of many centuries of yesteryear when a heavy ice sheath covered most of the northern hemisphere and eventually disappeared due to natural global warming. It did so without heavy industrial participation.

I am told we are (fortunately) in an interglacial, good conditions for "mammals" to engage in gardening, food production, and sunbathing 'n' stuff - I can't prove or disprove this and nor can any other animal with such an infinitesimally short lifespan as a human being, either. Shifts in magnetic north affect this, too, apparently. It'll get cold again, one eon or other, but until then it'll get hotter without human help, apparently.

What evidence can you present that shows mankind has contributed to the rise in the Earth's temperature?

Erm... Evidence? None, the same as you in the other direction. Neither of us stand outside with endless measurement equipment measuring everything possible to confirm or deny our beliefs for millenia and longer afaik- Anyway, in my opinion, perhaps telling are the copious and varied sources of data, collected by government agencies and independent researchers which are usually filtered down to the public via the media or ongoing peer-reviewed works like Wikipedia and whatever else you may read describing how endless use of air-conditioning - which grows by the year causes the expulsion of hot air from cooled homes and offices and is a real concern for sections of the scientific and environmentally-friendly community of fellow conspiracists about man-made warming.

I can prove to you that when I apply a voltage to a resistor or an e.g. silicon-based device or a piece of metal, they heat up. Much to many circuit and espcially IC designers' chagrin. You do actually make circuits sometimes, don't you? That's why electric kettles and boilers have a big piece of metal in them and electricity is passed through it - to heat a liquid up. From there we can extrapolate with absolute certainty of the theory being factual and irrefutable that a voltage passed through powerlines running across virtually every country (on this, the flat Earth, no doubt you'd like to argue next) and old-fashioned, non-fibre optic telecommunications cables made from copper or other wires made out of metals running across the floors of the seas and oceans are generating heat.

Previous post re-worded: Jane has a metal box placed outside on the ground at The Equator. She is also immortal. She can measure how it heats up 0.1ºC every 1,000 years (by measuring it with an electronic circuit that drifts 0.01ºC every 100 years - because a voltage is being applied to the components the electronic thermometer is composed of) until the Interglacial ends and then it will get colder. The nights at The Equator are not cold enough for the box to quite cool down each day to its original temperature, so the box ever so slowly heats up a little tiny bit naturally. John appears. John is a mean boy. He is the school bully. He puts a very, very thick, thinly-insulated wire underneath the box and passes a voltage through it. This adds 0.001ºC temperature rise to the interior of the box every 10 years. Now Jane's school project is all wrong - the maths don't add up anymore and she refuses to understand why because she doesn't want to see the wire John has placed there, no matter how much Bob, Judy, Tommy, Cherie and the rest of the gang keep pointing it out to her.

I could go on, but it's a waste of breath, and exhaling also contributes to the heating up of the planet, especially hot air.

I have no idea to whom you are referring, but I will say that whoever espouses evolution is wrong because evolution's premise is wrong.

The Hitch-Hiker's Guide to the Galaxy. ...Don't Panic... I'll say I'm with the Dogon on the theory of evolution, evolution is a lie made up by Homo Sapiens who strategically placed anatomically similar bits of bones in different rock strata to make the fallacy seem plausible. Monkeys never came down from a tree to pick up a juciy piece of fruit they dropped and as they did this more and more they became more upright, maybe. Just, "Beam me up, Scotty" seems not to work for most of us stuck down here.

Alternate take on evolution:

 

[wwfeldman]

Externet's original post:

Hi.
Along the years and the presence of educated professionals in this board; what is found as common electronics misconceptions that may need to be addressed as originated by voids in proper learning of electronics ?
In other words; what do you think should be changed in text books to facilitate understanding and to avoid mistakes - what would you change/improve ?

i think we're getting a bit far afield
i think its time to get back to electronics

 

[d123]

Hi,

i think we're getting a bit far afield
i think its time to get back to electronics

Agreed.

 

[Ratch]

Hi,



I am told we are (fortunately) in an interglacial, good conditions for "mammals" to engage in gardening, food production, and sunbathing 'n' stuff - I can't prove or disprove this and nor can any other animal with such an infinitesimally short lifespan as a human being, either. Shifts in magnetic north affect this, too, apparently. It'll get cold again, one eon or other, but until then it'll get hotter without human help, apparently.




Erm... Evidence? None, the same as you in the other direction. Neither of us stand outside with endless measurement equipment measuring everything possible to confirm or deny our beliefs for millenia and longer afaik- Anyway, in my opinion, perhaps telling are the copious and varied sources of data, collected by government agencies and independent researchers which are usually filtered down to the public via the media or ongoing peer-reviewed works like Wikipedia and whatever else you may read describing how endless use of air-conditioning - which grows by the year causes the expulsion of hot air from cooled homes and offices and is a real concern for sections of the scientific and environmentally-friendly community of fellow conspiracists about man-made warming.

I can prove to you that when I apply a voltage to a resistor or an e.g. silicon-based device or a piece of metal, they heat up. Much to many circuit and espcially IC designers' chagrin. You do actually make circuits sometimes, don't you? That's why electric kettles and boilers have a big piece of metal in them and electricity is passed through it - to heat a liquid up. From there we can extrapolate with absolute certainty of the theory being factual and irrefutable that a voltage passed through powerlines running across virtually every country (on this, the flat Earth, no doubt you'd like to argue next) and old-fashioned, non-fibre optic telecommunications cables made from copper or other wires made out of metals running across the floors of the seas and oceans are generating heat.

Previous post re-worded: Jane has a metal box placed outside on the ground at The Equator. She is also immortal. She can measure how it heats up 0.1ºC every 1,000 years (by measuring it with an electronic circuit that drifts 0.01ºC every 100 years - because a voltage is being applied to the components the electronic thermometer is composed of) until the Interglacial ends and then it will get colder. The nights at The Equator are not cold enough for the box to quite cool down each day to its original temperature, so the box ever so slowly heats up a little tiny bit naturally. John appears. John is a mean boy. He is the school bully. He puts a very, very thick, thinly-insulated wire underneath the box and passes a voltage through it. This adds 0.001ºC temperature rise to the interior of the box every 10 years. Now Jane's school project is all wrong - the maths don't add up anymore and she refuses to understand why because she doesn't want to see the wire John has placed there, no matter how much Bob, Judy, Tommy, Cherie and the rest of the gang keep pointing it out to her.

I could go on, but it's a waste of breath, and exhaling also contributes to the heating up of the planet, especially hot air.



The Hitch-Hiker's Guide to the Galaxy. ...Don't Panic... I'll say I'm with the Dogon on the theory of evolution, evolution is a lie made up by Homo Sapiens who strategically placed anatomically similar bits of bones in different rock strata to make the fallacy seem plausible. Monkeys never came down from a tree to pick up a juciy piece of fruit they dropped and as they did this more and more they became more upright, maybe. Just, "Beam me up, Scotty" seems not to work for most of us stuck down here.

Alternate take on evolution:

View attachment 153413

I hate to say it, but what you pontificate above is mostly blather. Please excuse me for being so direct.

Ratch

 

[asdf44]

A current has to have a voltage associated with it to pass through a resistance.

Ratch

A voltage also needs to have a current. Either in the form of leakage or the parasitic C of the node must have been charged with current in the past.


As another aside I think it's important to emphasize that learning means adding new models and ways of understanding something. It doesn't necessarily mean you need to replace your old models. Good engineers can bring many perspectives to bear on a single problem and know when to use each.

Thus it catches my attention when I see people imply a model is the 'right' model. Truth only matters so much, we might all be plugged into a matrix or exist in someone else dream....what matters is whether a model is useful and predictive. Sometimes simple models that are 'wrong' in some sense still serve that role.

For example you'll see people say "A square wave is the sum of multiple sin waves". But it's not. It can be usefully modeled as that in the frequency domain. But in the time domain it's just a square wave. Both are valid, neither is 'right'.


Which also relates to Evolution. Evolution denial is silly but also misses the point. At some level it doesn't matter whether we evolved or god created us. The theory of evolution explains things and predicts things (it predicted mutations and DNA 100 years early). Creationism predicts noting.

 

[d123]

I hate to say it, but what you pontificate above is mostly blather. Please excuse me for being so direct.

Ratch

Weak and meaningless blather as a riposte. Not only pompous but also a bad loser when trolling people on the wrong kind of forum who point out the emptiness of your argument(s) about topics unrelated to textbook improvements. Drop the act and be more of a person. Go pass a voltage through a resistor and cool down.

 

[Ratch]

A voltage also needs to have a current. Either in the form of leakage or the parasitic C of the node must have been charged with current in the past.

Not so, the terminals of a battery can have a voltage difference with no current present between them.

As another aside I think it's important to emphasize that learning means adding new models and ways of understanding something. It doesn't necessarily mean you need to replace your old models. Good engineers can bring many perspectives to bear on a single problem and know when to use each.

Who is advocating replacing old models?

Thus it catches my attention when I see people imply a model is the 'right' model. Truth only matters so much, we might all be plugged into a matrix or exist in someone else dream....what matters is whether a model is useful and predictive. Sometimes simple models that are 'wrong' in some sense still serve that role.

If a model is not correct or truthful, what the hell good is it? I don't understand what you mean by us being in someone's "dream". Do you have evidence of that?

For example you'll see people say "A square wave is the sum of multiple sin waves". But it's not. It can be usefully modeled as that in the frequency domain. But in the time domain it's just a square wave. Both are valid, neither is 'right'.

Your statement does not make sense. If both are valid, then both are correct.

Which also relates to Evolution. Evolution denial is silly but also misses the point. At some level it doesn't matter whether we evolved or god created us. The theory of evolution explains things and predicts things (it predicted mutations and DNA 100 years early). Creationism predicts noting.

Wrong! If evolution is wrong, then it explains nothing. If evolution does not exist, then creation is the only explanation. The premise of evolution relies on randomness organizing itself into a functional entity like the joke of an explosion in a print type factory making a dictionary. That never is going to happen.

Ratch

- - - Updated - - -

Weak and meaningless blather as a riposte. Not only pompous but also a bad loser when trolling people on the wrong kind of forum who point out the emptiness of your argument(s) about topics unrelated to textbook improvements. Drop the act and be more of a person. Go pass a voltage through a resistor and cool down.

I was hoping you would come up with thoughtful and cogent comments pertaining to the points you wanted to make.

Ratch

 

[d123]

Back to the subject at hand, I had a quick review of the contents of books I've used, which are:

The Art of Electronics (second edition)
Teach Yourself Electricty and Electronics (fifth edition)
Electronics - A Complete Course (second edition)
Electronics All-in-One For Dummies

In some senses, apart from general textbooks:
Analog Design Essentials W Sansen
Analysis and Design of Analog Integrated Circuits (fifth edition - cropped)
Current Sources and Voltage References
Assorted operational amplifier books by Analog, TI and so on.
...a few others I don't want to spend half the morning looking for in the laberynthine folders within folders within folders covering all manner of topics that "Circuits info." has become...

And looking at the first four titles, I couldn't comment on how ideas are conveyed accurately or intuitively but I think this is just such a diverse subject that it is hard to include everything necessary in one book without either skipping important details or making an encyclopedia. The need to understand diverse paths in electronics expands with each step taken by a learner. An ideal diode is "just" an op amp and a diode and a few resistors - can that be explained as a block or which should be explained first to avoid "it doesn't output exactly what was expected"...?

Second language teaching of English at least is/used to be taught with the premise of beginner, intermediate, upper-intermediate and advanced levels. Frustrating but convenient was explaining grammar such as tenses and modal verbs with truthful but misleadingly inaccurate generalisations for the first two levels then having to explain that what was taught was not quite the full picture and some textbook definitions verging on plain wrong, and then expounding on the full uses of a modal verb like will/would. Future tenses in British English are relatively complex in their subtlety of use and understanding when "will + verb" can imply prediction and it can imply certainty - you don't teach that aspect to a beginner, "will" is just for predictions... Not a nice method but expedient as otherwise the volume of information needed to be absorbed is overwhelming for the average person.

What's better for a rudimentary understanding and also not humiliating or demotivating a learner - a rough sketch of the facts or an in-depth analysis? I guess every subject from gardening through electronics or mechanics to brain surgery is the same...

 

[Ratch]

Back to the subject at hand, I had a quick review of the contents of books I've used, which are:

The Art of Electronics (second edition)
Teach Yourself Electricty and Electronics (fifth edition)
Electronics - A Complete Course (second edition)
Electronics All-in-One For Dummies

In some senses, apart from general textbooks:
Analog Design Essentials W Sansen
Analysis and Design of Analog Integrated Circuits (fifth edition - cropped)
Current Sources and Voltage References
Assorted operational amplifier books by Analog, TI and so on.
...a few others I don't want to spend half the morning looking for in the laberynthine folders within folders within folders covering all manner of topics that "Circuits info." has become...

And looking at the first four titles, I couldn't comment on how ideas are conveyed accurately or intuitively but I think this is just such a diverse subject that it is hard to include everything necessary in one book without either skipping important details or making an encyclopedia. The need to understand diverse paths in electronics expands with each step taken by a learner. An ideal diode is "just" an op amp and a diode and a few resistors - can that be explained as a block or which should be explained first to avoid "it doesn't output exactly what was expected"...?

Second language teaching of English at least is/used to be taught with the premise of beginner, intermediate, upper-intermediate and advanced levels. Frustrating but convenient was explaining grammar such as tenses and modal verbs with truthful but misleadingly inaccurate generalisations for the first two levels then having to explain that what was taught was not quite the full picture and some textbook definitions verging on plain wrong, and then expounding on the full uses of a modal verb like will/would. Future tenses in British English are relatively complex in their subtlety of use and understanding when "will + verb" can imply prediction and it can imply certainty - you don't teach that aspect to a beginner, "will" is just for predictions... Not a nice method but expedient as otherwise the volume of information needed to be absorbed is overwhelming for the average person.

What's better for a rudimentary understanding and also not humiliating or demotivating a learner - a rough sketch of the facts or an in-depth analysis? I guess every subject from gardening through electronics or mechanics to brain surgery is the same...

What is the point you are trying to make in the above post?

Ratch

 

[dick_freebird]

2) Ohm's law wrongly taught as R=E/I. R=E/I is the definition of resistance, not Ohm's law. A resistance follows Ohm's law if its value is constant over a reasonable current range. In other words, if its resistance is linear. This is expounded in physics books written by Halliday & Resnick, and Raymond Serway. A tungsten wire follows Ohm's law. A semiconductor junction does not.

Tungsten wire does not have a linear resistance. Go measure
cold resistance and then measure V/I at working power level
in a light bulb.

3) Wrongfully claiming that the base current of a BJT controls the collector current. The BE voltage controls the collector current. The base current is the waste current that is somewhat proportional to the collector current, but it is the base leakage effect, not the cause of the of the collector current. The primary cause of the collector current is the BE voltage. A BJT is a transconductance element.

This topic inspires a lot of religiosity and I'm not going to argue
with any of you about it (again), only to say that I was taught
another way and that offers a much more useful intuition of the
goings-on. With a credible physics basis. Having done a few tens
of bipolar IC product designs and having some device physics
background (stale as it may be) I don't care what the peanut
gallery or any nut in particular has to say about who's wrong.

I think this thread has passed beyond usefulness and consists
of mostly posing and bickering.

 

[Ratch]

2) Ohm's law wrongly taught as R=E/I. R=E/I is the definition of resistance, not Ohm's law. A resistance follows Ohm's law if its value is constant over a reasonable current range. In other words, if its resistance is linear. This is expounded in physics books written by Halliday & Resnick, and Raymond Serway. A tungsten wire follows Ohm's law. A semiconductor junction does not.

Tungsten wire does not have a linear resistance. Go measure
cold resistance and then measure V/I at working power level
in a light bulb.

3) Wrongfully claiming that the base current of a BJT controls the collector current. The BE voltage controls the collector current. The base current is the waste current that is somewhat proportional to the collector current, but it is the base leakage effect, not the cause of the of the collector current. The primary cause of the collector current is the BE voltage. A BJT is a transconductance element.

This topic inspires a lot of religiosity and I'm not going to argue
with any of you about it (again), only to say that I was taught
another way and that offers a much more useful intuition of the
goings-on. With a credible physics basis. Having done a few tens
of bipolar IC product designs and having some device physics
background (stale as it may be) I don't care what the peanut
gallery or any nut in particular has to say about who's wrong.

I think this thread has passed beyond usefulness and consists
of mostly posing and bickering.

You think wrong. NASA gets around by "walking" in space, even though it looks more like they are floating outside of their space ships. You will design better circuits knowing how BJTs really work. Read this post by Winfield Hill, author of The Art of Electronics. https://cr4.globalspec.com/thread/68055/Voltage-vs-Current#comment720374 .

Ratch

 

[c_mitra]

Tungsten wire does not have a linear resistance. Go measure cold resistance and then measure V/I at working power level in a light bulb.

Linearity of resistance is not usually understood in terms of temp (which is an external parameter that must be held constant); it should be understood in terms of V and I.

If you plot V/I for a sample of tungsten wire at any given fixed temp, the graph is expected to be linear over a substantial range of voltage and current. That is what we understand by linearity of V/I graphs.

For a diode, say, the graph is not linear and we do not (usually) talk about resistance but the basic concept is applicable if you specify the voltage/current point in the graph. In that case, the resistance varies with applied voltage.

By the way, modern definitions (say SI units) have moved around in recent times around the fundamental constants; see, e.g., the definitions of voltage and current.