Bulbs connected in series. Physics doesn't add up

[chris_leyson]

On the subject of negative resistance you could try building a Lambda diode using p-channel and j-channel jfets. Works at a higher voltage than tunnel diodes but cheaper.

https://en.m.wikipedia.org/wiki/Lambda_diode

[m k]

Ohm's Law is an approximation that is accurate for "ohmic" devices, i.e. those that obey Ohm's Law.

I think I've always treated R=U/I sort of fundamentally abstract thing.
When that is then connected to reality the real R is not really present, it's a combination of other two definitions.
Seems that my real R is always unknown.

Where's that resistor story by Edwin Pettis when you need it.

[radiolistener]

Good to see you acknowledge the existence and properties of tunnel diodes

I already explained this nonlinear properties before you provided example with tunnel diode.

There is no such thing as "conventional resistive behaviour". There are measured V-I curves, and several mathematical models are used to explain aspects of the measurements.

I apologize for the confusing terminology, when I referred to 'conventional resistive behavior' I actually mean 'Ohmic resistance behavior'.

Different mathematical models are useful in different situations, as is typical with any kind of model of physical behaviour. Many people have a naive mis-understanding of the models' applicability.

Indeed, this aligns with my earlier points and emphasizes the importance of understanding the distinction between linear and nonlinear components, particularly regarding the applicability of Ohm's Law. I explained it before your objection.

While you may find the use of the term "Ohm's Law" in the context of nonlinear components somewhat objectionable, it's important to clarify that I talk not about predicting the behavior of the component across varying voltages using Ohm's Law. Instead, I talk about the relationship between voltage and current through resistance as it experessed in Ohm's law equation. This relationship can be used at a specific operating point to find the dynamic resistance, even in nonlinear systems.

You previously mentioned that it would be more appropriate to use different notations for resistance, current, and voltage of nonlinear component: Rdynamic​, dv, and di instead of R, U, and I. However, I don't see much value in distinguishing the notation for resistance, voltage, and current between nonlinear and linear components.

In my point of view, what is more important - is not the specific symbols used to denote current and voltage, but rather the understanding of the distinction between linear and nonlinear component properties.

[BeBuLamar]

I have a suggestion. In experiment #3 instead of 2.5V use 5V and you see everything is right.

[tggzzz]

Ohm's Law is an approximation that is accurate for "ohmic" devices, i.e. those that obey Ohm's Law.

I think I've always treated R=U/I sort of fundamentally abstract thing.
When that is then connected to reality the real R is not really present, it's a combination of other two definitions.
Seems that my real R is always unknown.

Where's that resistor story by Edwin Pettis when you need it.

Ohm's law is a model of how some materials behave, no more, no less. "All models are wrong, but some are useful". In addition, all models have their limits.

All non-superconducting materials have more or less resistance. That doesn't mean there is a linear V-I relationship in which assigning a constant resistance makes sense.

[tggzzz]

Good to see you acknowledge the existence and properties of tunnel diodes

I already explained this nonlinear properties before you provided example with tunnel diode.

There is no such thing as "conventional resistive behaviour". There are measured V-I curves, and several mathematical models are used to explain aspects of the measurements.

I apologize for the confusing terminology, when I referred to 'conventional resistive behavior' I actually mean 'Ohmic resistance behavior'.

Different mathematical models are useful in different situations, as is typical with any kind of model of physical behaviour. Many people have a naive mis-understanding of the models' applicability.

Indeed, this aligns with my earlier points and emphasizes the importance of understanding the distinction between linear and nonlinear components, particularly regarding the applicability of Ohm's Law. I explained it before your objection.

While you may find the use of the term "Ohm's Law" in the context of nonlinear components somewhat objectionable, it's important to clarify that I talk not about predicting the behavior of the component across varying voltages using Ohm's Law. Instead, I talk about the relationship between voltage and current through resistance as it experessed in Ohm's law equation. This relationship can be used at a specific operating point to find the dynamic resistance, even in nonlinear systems.

You previously mentioned that it would be more appropriate to use different notations for resistance, current, and voltage of nonlinear component: Rdynamic​, dv, and di instead of R, U, and I. However, I don't see much value in distinguishing the notation for resistance, voltage, and current between nonlinear and linear components.

In my point of view, what is more important - is not the specific symbols used to denote current and voltage, but rather the understanding of the distinction between linear and nonlinear component properties.

Have you ever taken a course in differential calculus and passed?

If you had, you would understand there is a fundamental difference between a curve and the slope of the curve. In this case, that's V/I and dV/dI. If you can't see the difference between the two, presumably you also think distance and speed are the same as each other.

https://electronics.stackexchange.com/questions/498402/what-is-the-difference-between-differential-resistance-and-resistance#498404
https://en.wikipedia.org/wiki/Electrical_resistance_and_conductance#Static_and_differential_resistance

I was taught that in the first two weeks at university.

[coppice]

Incandescent bulbs are interesting when powered by AC. The temperature of the filament ripples a lot through each half cycle of the power source. So, the resistance is changing a lot. So, the device is not linear. It is not a true "resistive load". How much does that affect things? It depends on details of the exact bulb, but when you have a clean sine wave power source, and look at the current waveform you usually find 10%-25% THD. To someone who understands what is going on, but has never tried measuring it, the size of that THD figure is often surprising.

[radiolistener]

Ohm's law is a model of how some materials behave, no more, no less. "All models are wrong, but some are useful". In addition, all models have their limits.

All non-superconducting materials have more or less resistance. That doesn't mean there is a linear V-I relationship in which assigning a constant resistance makes sense.

As m k previously mentioned, resistance, current, and voltage are abstract concepts used as models to describe electrical behavior rather than physical entities. What fundamentally matters here is the relationship between voltage and current, or more broadly, the relationship between electric field strength and magnetic field strength in the context of electromagnetic waves.

This ratio, which we conventionally call resistance and measure in Ohms, remains significant for both linear and nonlinear components.

To clarify, I am not referring to the Ohmic properties typical of a linear component like a resistor, but rather to the relationship between voltage and current as an important characteristic of the component at a specific operating point.

Although a nonlinear component is not an Ohmic component, the ratio of voltage to current across it still plays the same important role as it does for a linear component, despite the fact that this ratio may vary differently with voltage/current compared to a linear component.

[tggzzz]

Incandescent bulbs are interesting when powered by AC. The temperature of the filament ripples a lot through each half cycle of the power source. So, the resistance is changing a lot. So, the device is not linear. It is not a true "resistive load". How much does that affect things? It depends on details of the exact bulb, but when you have a clean sine wave power source, and look at the current waveform you usually find 10%-25% THD. To someone who understands what is going on, but has never tried measuring it, the size of that THD figure is often surprising.

As I'm sure you know, the amount of temperature variation (and hence distortion) will depend on the frequency and the thermal mass. Bill Hewlett famously took that into account in the HP200A oscillator

[tggzzz]

Ohm's law is a model of how some materials behave, no more, no less. "All models are wrong, but some are useful". In addition, all models have their limits.

All non-superconducting materials have more or less resistance. That doesn't mean there is a linear V-I relationship in which assigning a constant resistance makes sense.

As m k previously mentioned, resistance, current, and voltage are abstract concepts used as models to describe electrical behavior rather than physical entities. What fundamentally matters here is the relationship between voltage and current, or more broadly, the relationship between electric field strength and magnetic field strength in the context of electromagnetic waves.

This ratio, which we conventionally call resistance and measure in Ohms, remains significant for both linear and nonlinear components.

To clarify, I am not referring to the Ohmic properties typical of a linear component like a resistor, but rather to the relationship between voltage and current as an important characteristic of the component at a specific operating point.

Although a nonlinear component is not an Ohmic component, the ratio of voltage to current across it still plays the same important role as it does for a linear component, despite the fact that this ratio may vary differently with voltage/current compared to a linear component.

You're getting there, but while it can be said that a non-linear material/device has resistance, it is confusing to the point of being meaningless to measure it in Ohms. Ohm's has a meaning in the context of Ohm's Law, and that requires a linear material/device.
 
If you have difficulty with that, then using your concept of resistance, is that resistance of the this component positive, negative, zero, or infinite? (Hint: for your concept, it is all of them)



Now do you see why your concept of R=V/I is meaningless?

[TimFox]

Negative resistance devices and circuits, where dV/dI < 0, are both interesting and useful.
These include two-terminal devices, such as tunnel diodes, and more complicated circuits such as vacuum-pentode transitrons and op-amp circuits with positive feedback.
It is important to note that to exhibit negative conductance across the two terminals, all of these circuits require external power:  the bias voltage for a tunnel diode oscillator, the plate and screen voltages for the transitron, etc.
A passive non-linear device, such as a PN diode, has an incremental resistance (slope or AC resistance) dV/dI > 0 without external power.

[TimFox]

Big hint: Ohm's law only applies to ohmic devices. Ohm's law does not apply to non-ohmic devices. That is simple and unambiguous, and I would have thought uncontroversial.

What is an ohmic device?  A device that behaves according to ohm's law.

Seems like a circular argument to me.

https://yourlogicalfallacyis.com/begging-the-question

Not an argument, simply a statement of the obvious.

The key point is that not all devices/materials are ohmic, and for such devices/materials V is not linearly proportional to R, as implied by V=IR.

Ohm's Law is applicable to a huge set of practical devices, such as wires, which are then defined as "ohmic".
This is not circular, merely a definition of "ohmic".
Other devices are non-ohmic and Ohm's Law itself is not applicable.
The SI unit "ohm" is defined as volts/amperes, in the same way that the volt is defined as joules/coulombs, but those definitions are not "laws".

[coppice]

Incandescent bulbs are interesting when powered by AC. The temperature of the filament ripples a lot through each half cycle of the power source. So, the resistance is changing a lot. So, the device is not linear. It is not a true "resistive load". How much does that affect things? It depends on details of the exact bulb, but when you have a clean sine wave power source, and look at the current waveform you usually find 10%-25% THD. To someone who understands what is going on, but has never tried measuring it, the size of that THD figure is often surprising.

As I'm sure you know, the amount of temperature variation (and hence distortion) will depend on the frequency and the thermal mass. Bill Hewlett famously took that into account in the HP200A oscillator

You might expect that after a century of high volume production the design of incandescent bulbs would have converged to essentially a single design. However, I found (while doing work on power quality instrumentation) that if you try different makes of bulb of the same power rating the THD can vary quite a bit on the same supply. Whether that is due to variation in the thermal mass, the thermal conduction paths, or the IR transparency of the glass I never investigated.

[radiolistener]

Ohm's has a meaning in the context of Ohm's Law, and that requires a linear material/device.

You view the Ohm unit in a narrow context, considering it solely as a concept of resistance that applies meaningfully only to linear components with Ohmic resistance. In contrast, I see the Ohm unit in a broader context - as the ratio of voltage to current or the ratio of electric field strength to magnetic field strength. This ratio reflects the constant relationship for linear components with Ohmic resistance (which we know as classic Ohm's law), but it also applies to both linear and nonlinear components at selected voltage and current levels. This perspective, while extending beyond the classical interpretation of Ohm's Law, continues to address the same fundamental essence expressed as the relationship between voltage and current. It emphasizes the intrinsic physical nature of this relationship, which significantly impacts the efficiency of energy transfer from the source to the receiver.

For example, the characteristic impedance of the environment surrounding an antenna is also expressed in Ohms. However, this impedance is varying within the near-field region and, even in the far-field region it depends on the properties of the surrounding environment. Does this mean that we cannot express it in Ohms?

[IanB]

You view the Ohm unit in a narrow context, considering it solely as a concept of resistance that applies meaningfully only to linear components with Ohmic resistance. In contrast, I see the Ohm unit in a broader context - as the ratio of voltage to current or the ratio of electric field strength to magnetic field strength. This ratio reflects the constant relationship for linear components with Ohmic resistance (which we know as classic Ohm's law), but it also applies to both linear and nonlinear components at selected voltage and current levels. This perspective, while extending beyond the classical interpretation of Ohm's Law, continues to address the same fundamental essence expressed as the relationship between voltage and current. It emphasizes the intrinsic physical nature of this relationship, which significantly impacts the efficiency of energy transfer from the source to the receiver.

You forget a fundamental aspect of physics that Ohm's Law is a physical Law. A law in physics is a model that holds over a wide range of experimental conditions, and can be used to make predictions. Ohm's Law says that for many materials, voltage is proportional to current, all other variables remaining constant. Thus, if you know the constant of proportionality, you can predict the voltage given a measurement of current, or you can predict the current given a measurement of voltage.

If the relation between voltage and current is not a straight line graph passing through the origin, then the material does not follow Ohm's Law, rather it follows some other, more complex Law.

[TimFox]

Yes, the "Ohm" as a unit in electricity is more general than in circuits that obey Ohm's Law.
The unit is merely the quotient of two other units:  1 Ohm = 1 Volt/Ampere, and can be used also for the derivative dV/dR.
Standards labs maintain carefully built two-terminal objects calibrated in Ohms to international standards.
Similarly, the Hertz was defined as one cycle/second, the Volt as one Joule/Coulomb, etc. to define the terms.
The laws of electromagnetism give relations between different properties such as potential, current, charge, etc. and different fields such as E, D, B, and H (vectors).
Relationships between the latter four fields will be written differently depending on the choice of units:  SI (rationalized MKS), "Gaussian" (unrationalized cgs), and several others that are rarely chosen now.

[tggzzz]

Ohm's has a meaning in the context of Ohm's Law, and that requires a linear material/device.

You view the Ohm unit in a narrow context, considering it solely as a concept of resistance that applies meaningfully only to linear components with Ohmic resistance. In contrast, I see the Ohm unit in a broader context - as the ratio of voltage to current or the ratio of electric field strength to magnetic field strength. This ratio reflects the constant relationship for linear components with Ohmic resistance (which we know as classic Ohm's law), but it also applies to both linear and nonlinear components at selected voltage and current levels. This perspective, while extending beyond the classical interpretation of Ohm's Law, continues to address the same fundamental essence expressed as the relationship between voltage and current. It emphasizes the intrinsic physical nature of this relationship, which significantly impacts the efficiency of energy transfer from the source to the receiver.

For example, the characteristic impedance of the environment surrounding an antenna is also expressed in Ohms. However, this impedance is varying within the near-field region and, even in the far-field region it depends on the properties of the surrounding environment. Does this mean that we cannot express it in Ohms?

That reads like Post-Modern Literature Criticism

What you "see" is your own set of rationales and definitions. While that might be OK when conversing with yourself, it doesn't work if you want to converse with other people. For a conversation it is necessary to have common definitions of words and concepts.

Now, again, how do you "see" the resistance of the battery? Positive, negative, zero, infinite. Your "vision" of R=V/I requires that it is all of those - which is useless for any practical purpose.



Hint: better people than us worked through chains of reasoning such as yours, 1 to 2 centuries ago. Stand on their shoulders, don't trip over their discarded toenail clippings

[TimFox]

There is an anecdote circulating on-line about a new employee who was told not to spell "hamster" as "hampster" but refused to change because that's the way she spelled it.

[tggzzz]

There is an anecdote circulating on-line about a new employee who was told not to spell "hamster" as "hampster" but refused to change because that's the way she spelled it.

Excellent

Maybe the rodents were always found in hampers?

[themadhippy]

told not to spell "hamster" as "hampster"

maybe it was a  siberian hampster

[TimFox]

with a paedigree

[djsb]

From Hempstead 

[Xena E]

It's not a hampster, it's a rhat!

[TimFox]

That's why we put basil in the ratatouille ...

[radiolistener]

That's why we put basil in the ratatouille ...

Is it rational to start with ratatouille and finish with ratsberry pie?