Problem of electricity and electrons

[platyhelminth]

Hi, the today definition of electric current says it is done by moving electrons. But this wikipedia article https://en.wikipedia.org/wiki/Speed_of_electricity says:
"the signals or energy travel as electromagnetic waves typically on the order of 50%–99% of the speed of light, while the electrons themselves move (drift) much more slowly."
"AC voltages cause no net movement; the electrons oscillate back and forth in response to the alternating electric field"

This comment about AC voltages remember us that the inventor of the AC induction motor, Tesla, didn't believe in the existence of the electron https://en.wikipedia.org/wiki/Nikola_Tesla#On_experimental_and_theoretical_physics

In order to prove or disprove the existence of electrons in electric current I searched the internet if the discharged plate of a capacitor lose mass and if a charged plate of a capacitor gain mass. The experiment was never made. The mass is considered negligible but we have to measure it to show that electricity is an actual movement of electron (it should be feasible with today instruments and a big capacitor to have lot of electron involved)

Additional info :
_how the notion of electron was accepted https://www.nobelprize.org/educational/physics/vacuum/experiment-1.html
_formula to evaluate electron speed https://en.wikipedia.org/wiki/Drift_velocity "Therefore in this wire the electrons are flowing at the rate of 23 µm/s. At 60 Hz alternating current, this means that within half a cycle the electrons drift less than 0.2 μm. In other words, electrons flowing across the contact point in a switch will never actually leave the switch."

 

[Nugatory]

(it should be feasible with today instruments and a big capacitor to have lot of electron involved)

Don't guess when you can calculate.
What is the difference in the weight of a plate of a 1F capacitor when discharged and when charged to a few tens of kV, and how much is that as a fraction of the total weight of the capacitor? You can make reasonable assumptions about the size and weight of the capacitor.

However, we don't need this experiment to satisfy ourselves that electrons are the charge carriers in ordinary electrical circuits. There are plenty of other experiments that support the existence of electrons and their role as charge carriers, and plausible alternative theories that match the results of these experiments.

 

[Dale]

In order to prove or disprove the existence of electrons in electric current I searched the internet if the discharged plate of a capacitor lose mass and if a charged plate of a capacitor gain mass.

A far better experiment is measuring the Hall effect.

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

https://www.nist.gov/pml/engineering-physics-division/hall-effect-measurements-introduction

 

[mfb]

What is the difference in the weight of a plate of a 1F capacitor when discharged and when charged to a few tens of kV, and how much is that as a fraction of the total weight of the capacitor? You can make reasonable assumptions about the size and weight of the capacitor.

And compare the change in gravitational force to the change in force between the capacitor plates.

Hi, the today definition of electric current says it is done by moving electrons.

In most but not all materials electrons are the moving charges.
You can calculate the conductivity of materials based on the number of free electrons in the material.

Tesla had a lot of weird ideas, and we learned more in the last 100 years. How would CRT monitors work without electrons, for example?

"the signals or energy travel as electromagnetic waves typically on the order of 50%–99% of the speed of light, while the electrons themselves move (drift) much more slowly."

That is (sort of) correct. What is your point?

 

[platyhelminth]

Don't guess when you can calculate.
What is the difference in the weight of a plate of a 1F capacitor when discharged and when charged to a few tens of kV, and how much is that as a fraction of the total weight of the capacitor? You can make reasonable assumptions about the size and weight of the capacitor.

we have F=C/V . We need to know the value of coulomb to have the quantity of electrons. For 10 000V we would have 10 000C for 1F. For -1C meaning 6.242×10^18 electrons we would have 6.242×10^22 electrons in -10 000C. With the accepted mass of an electron ( 9.10938356 × 10-31 kg) we would have 5.68607722x10^-8 kg of electrons. The Copper has one free electron per atom we would have 6.242×10^22 atoms (0.1036508469mol) of copper in each plate thus, with a atomic weight of 63.546 g/mol, 0.00658659671kg. The ratio difference of weight would be 0.0000086328

I am not a physicist. I could have mistaken in some points.

A far better experiment is measuring the Hall effect.

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

https://www.nist.gov/pml/engineering-physics-division/hall-effect-measurements-introduction

Hall effect was discovered 18 years before the electron discovery. It has been reinterpreted after electron discovery.

And compare the change in gravitational force to the change in force between the capacitor plates.In most but not all materials electrons are the moving charges.
You can calculate the conductivity of materials based on the number of free electrons in the material.

Tesla had a lot of weird ideas, and we learned more in the last 100 years. How would CRT monitors work without electrons, for example?
That is (sort of) correct. What is your point?

So for you electricity is at the same time a electromagnetic wave (a photon ?) traveling at the speed of light and moving electrons traveling at µm/s ? The calculation here https://en.wikipedia.org/wiki/Drift_velocity#Numerical_example was made with an AC of 60hz but AC voltage can alternate at tens to thousands of megahertz https://en.wikipedia.org/wiki/Alternating_current#Information_transmission making electron nearly immobile. I guess you will ask me to calculate how much the electron would move (or oscillate) in such a case and if the distance is inferior to the size of an orbital (making AC a quantum phenomenon, if electron exist lol. And I wonder if the "electric conductivity of the medium at the temperature considered" of the drift velocity formula apply)

 

[mfb]

You cannot make a 1 F, tens of kV capacitor with 6 gram of copper.

Hall effect was discovered 18 years before the electron discovery. It has been reinterpreted after electron discovery.

The results of the experiment were better understood later. What exactly is your point?

So for you electricity is at the same time a electromagnetic wave (a photon ?) traveling at the speed of light and moving electrons traveling at µm/s ?

See the "sort of". Changes in the electric potential propagate at speeds of the order of the speed of light, while the net motion of electrons is very slow, yes.

If you push a metal bar, the end will start moving quickly, even if the bar with all its atoms is moving very slowly, and the two speeds are unrelated. This is similar to motion of electrons in a conductor.

 

[platyhelminth]

You cannot make a 1 F, tens of kV capacitor with 6 gram of copper.

I think i forgot capacitance (and considered that each copper atom is charged) https://en.wikipedia.org/wiki/Capacitance

 

[mfb]

A rough estimate: We want to put the plates on independent scales, so we cannot combine them with a dielectric in between. Let's make a 0.5 mm gap filled with SF6 at high pressure to avoid an electric arc. Then we need 50 km² for our plate capacitor.

A 1 nm thick layer of copper with this area has a mass of 500 kg.

It gets worse. The two plates attract each other with 2*10¹¹ N. The 1 nm foil doesn't have any relevant structural strength. You need a huge support structure to keep the foils apart, increasing the mass by orders of magnitude.
You can save a factor 2 by interleaving the plates, but it should be obvious that the project is completely infeasible.What you can do is measure field emission of negatively charged spiky things: If you push too many electrons in, they get ejected into the environment.

 

[Nugatory]

I think i forgot capacitance (and considered that each copper atom is charged) https://en.wikipedia.org/wiki/Capacitance

Yes, but it doesn't matter. These additional considerations just mean that the ratio is even smaller than the 1 part in 100,000 that you calculated above, and that ratio is already far below what is practical to measure (Remembering that we have to separate this effect from the electrostatic force between the two plates, and considering the physical characteristics of a 1F 10Kv capacitor).

We do the calculation to check whether this might be a practical experiment, and we have our answer without investing any more work in it.

 

[Dale]

Hall effect was discovered 18 years before the electron discovery. It has been reinterpreted after electron discovery.

And what is your point? The Hall effect is one of the reasons that we know about electrons. It was one of the main effects that electrons explain. Sometimes an effect is discovered first and then a model is developed to explain it and sometimes the model is developed first and then effects predicted by the model are discovered later. The order doesn't matter much.

In any case, the Hall effect demonstrates conclusively that the charge carriers in metals are negative. What else do you want to show?

 

[platyhelminth]

Ok,
If what I said about AC current (which is mostly quotes of wiki) is true and that the Hall effect is truly measuring charges carriers movements. Then hall effect would be unable to measure AC current above a certain frequency since electrons would oscillate in a very small distance. Likely considered immobile

 

[Dale]

Then hall effect would be unable to measure AC current above a certain frequency

Please post a valid reference for this claim.

 

[mfb]

The distance doesn't really matter, the force on the electrons is independent of the distance they move during a cycle, it only depends on the current and the material. You cannot measure the Hall effect properly if the frequency is too high, because the voltage changes its polarity too often and voltage measurements need some time. So what? This is mainly an experimental limitation.

 

[DarioC]

Say there OP, thanks so much for the link to electron drift. I have played around with calculations involving a 1 mm square wire and movement of "free electrons" through it for some time. Somehow never ran across that formula. Duh.

When you think about electrons "bumping" from one valence shell to another in even a very small wire and do calculations on how many valence electrons are present in a single cross section of the wire, it is mind boggling. I am speaking of a copper wire with one electron in the outer shell.

My crude calculations indicate that if one Ampere was fed into the wire one electron at a time in line through the length of the wire it would take seconds for a given electron to move through a 1 meter long wire.

If you did the same by "bumping" one cross-section worth of electrons at a time to move one cross-section out the other end of the wire, it would take years for one electron in a given cross-section to get to the other end of the wire (at one Ampere current flow).

Likely the interval is somewhere in between. I think I will be amusing myself with that formula for a quite some time.

 

[platyhelminth]

Please post a valid reference for this claim.

http://en-us.fluke.com/training/tra...p-meters/inside-hall-effect-clamp-meters.html

Hall Effect clamp meters can measure both ac and dc current up to the kilohertz (1000 Hz) range..

It seems to concern a commercial tool.

https://en.wikipedia.org/wiki/Hall_effect_sensor

It can be operated up to 100 kHz.

spurious signals systematic errors:
http://aip.scitation.org/doi/abs/10.1063/1.1657320

The distance doesn't really matter, the force on the electrons is independent of the distance they move during a cycle, it only depends on the current and the material. You cannot measure the Hall effect properly if the frequency is too high, because the voltage changes its polarity too often and voltage measurements need some time. So what? This is mainly an experimental limitation.

May be.

This thread was manly motivated on my side by the difference of electicity as a electromagnetic wave speed-of-light and electricity as µ movement of electrons. Before recently I always believed electricity was purely electron movement done at the speed of light. I was wrong and came in that forum when I noticed that.

I think I will be amusing myself with that formula for a quite some time.

Please if you can, mesure the movement of electrons in a cycle of AC voltages alternating tens to thousands of megahertz. And confirm or not that it is smaller than an orbital.

 

[Dale]

spurious signals systematic errors:
http://aip.scitation.org/doi/abs/10.1063/1.1657320

Looks like a good article. I can't read more than the abstract.

This thread was manly motivated on my side by the difference of electicity as a electromagnetic wave speed-of-light and electricity as µ movement of electrons. Before recently I always believed electricity was purely electron movement done at the speed of light.

That is a pretty common misconception. The fields travel at nearly the speed of light, but not the charge carriers. The energy is also transported in the fields, not as little packets of energy attached to the charge carriers.

The Hall effect can be directly used to determine the charge carrier charge density. With that you can calculate the velocity of the charge carriers, even without a notion of an electron (i.e. as a classical continuum of charge carriers)

 

[DarioC]

I think you mean calculate, not measure? Would be interesting to calculate the minimum frequency movement that would equate to the orbital dimension of the valence electron for a given conductor. Does that make any sense?

 

[mfb]

And confirm or not that it is smaller than an orbital.

That doesn't matter.
(a) it is a motion of unbound electrons, they are not localized at an atom
(b) it is an average motion. It doesn't even make sense to assign positions to individual electrons

 

[davenn]

My crude calculations indicate that if one Ampere was fed into the wire one electron at a time in line through the length of the wire it would take seconds for a given electron to move through a 1 meter long wire.

that makes no sense at all
you misunderstand what Amps and current is ... you Don't feed 1 amp into a length of wire ( or other circuit) and you cannot do it 1 electron at a time
the current through a circuit is determined by the resistive load of the circuit

google the definitions of ampereDave

 

[DarioC]

Of course one electron at a time doesn't make sense, but when one is thinking about what actually is going on in the wire, not just a formula, you think about all the possibilities. As in max and minimum. I do anyway. As to "feeding" one amp into a wire perhaps you could explain to me whether it is push or pull. Chuckle.

After looking at the formula for the drift rate through a wire due to a voltage I notice that there is no temperature value there. Interesting considering that for "normal" conditions that the thermal movement of valence electrons is much larger that that due to current flow. Seems that would mean that while the electrons might move "forward" the distance given in one second, they might be moving in some other direction multiple times that value due to thermal excitement.

Think I have to check on thermal excitation again. Actually I think where I got that from was a comment in a research paper on electrons and current flow.

On the google definition lookup, I probably should mention that I calibrated the electronics equipment that was used in designing and building the antennas that went to the moon. Both of them. chuckle.

 

[davenn]

. As to "feeding" one amp into a wire perhaps you could explain to me whether it is push or pull. Chuckle.

reread my earlier comment

the current through a circuit is determined by the resistive load of the circuit

Seems that would mean that while the electrons might move "forward" the distance given in one second, they might be moving in some other direction multiple times that value due to thermal excitement.

with no voltage ( potential ) applied across the wire, the free electrons are moving randomly in ALL directions. Applying a voltage across the wire doesn't stop the free electron random movement. It just causes a general drift in one direction.

 

[Quandry]

If you push a metal bar, the end will start moving quickly. even if the bar with all its atoms is moving very slowly, and the two speeds are unrelated. This is similar to motion of electrons in a conductor.

I have taken this out of context of the thread - but the statement fascinated me. Can you expand on this?

 

[cnh1995]

I have taken this out of context of the thread - but the statement fascinated me. Can you expand on this?

Suppose the bar is at rest on a frictionless surface and say its two ends are A and B. Now, if you gave a slight push to the bar on end A, it will start moving in the direction of the push. End B of the bar, although not "directly" pushed, will start moving simultaneously with A. Now the velocity of the entire bar is very small (because of the 'slight' push), but the velocity of the 'push' signal from end A to end B is considerably high as both the ends (and entire bar) start moving almost at the same time. That speed has nothing to do with the speed at which the bar is moving.

Similarly, in electric circuits, drift speed (mm/s) and the speed of energy transfer are unrelated.
Electrons do not carry the energy. It's the fields (E and B) that carry the energy. The speed of energy transfer is nearer to the speed of light.

 

[Quandry]

Suppose the bar is at rest on a frictionless surface and say its two ends are A and B. Now, if you gave a slight push to the bar on end A, it will start moving in the direction of the push. End B of the bar, although not "directly" pushed, will start moving simultaneously with A. Now the velocity of the entire bar is very small (because of the 'slight' push), but the velocity of the 'push' signal from end A to end B is considerably high as both the ends (and entire bar) start moving almost at the same time. That speed has nothing to do with the speed at which the bar is moving.

Similarly, in electric circuits, drift speed (mm/s) and the speed of energy transfer are unrelated.
Electrons do not carry the energy. It's the fields (E and B) that carry the energy. The speed of energy transfer is nearer to the speed of light.

OK, it was, for me, a semantic misunderstanding. When you said the 'end will move quickly' which to me indicates speed , where I would say 'would quickly (begin to) move' which indicates time. Funny old thing language, isn't it.

 

[cnh1995]

When you said the 'end will move quickly'

I didn't say that, mfb did.

 

[mfb]

I didn't say that either, I said "the end will start moving quickly". If you push a 1 meter long steel rod at one end, the other end will start moving after about 200 microseconds.

 

[Drakkith]

After looking at the formula for the drift rate through a wire due to a voltage I notice that there is no temperature value there. Interesting considering that for "normal" conditions that the thermal movement of valence electrons is much larger that that due to current flow. Seems that would mean that while the electrons might move "forward" the distance given in one second, they might be moving in some other direction multiple times that value due to thermal excitement.

That is indeed an apt description of what is going on. The thermal motion of the electrons in the conduction band of the conductor are random and much, much larger than the drift velocity. This is because drift velocity is only an average net motion of a large number of electrons under the application of an electric field.

 

[sophiecentaur]

I didn't say that either, I said "the end will start moving quickly". If you push a 1 meter long steel rod at one end, the other end will start moving after about 200 microseconds.

This can also be related to the speed of sound in the material. One end can be hit very fast (higher than the wave speed if the force is high enough) over a very small distance, which can cause a shock wave but that will soon slow down to the wave speed.