Veritasium "How Electricity Actually Works"

[electrodacus]

Electrodacus has agreed that there is power available to do work in the return circuit. And that this current flowed in and out of  the capacitor terminals.   As to whether this power went "through" the capacitor i guess we will never agree. 

Am I correct ?

The energy will go in a capacitor when it is charged and out of the capacitor when it is discharged. There will never be a case where energy goes through capacitor unless the capacitor is defective in the sense that plates are shorted.
Energy flows through a resistor / wire but flows in or out of a capacitor.


As I see that problem was not solved I will provide the correct results.

12V ideal voltage power supply no internal resistance
2x 0.5Ohm wires connecting a 1000uF capacitor also with no significant DC ESR compared to wire resistance so we ignore for simplicity.

Initial connection we get:
The supply providing 144mWs in order to charge the capacitor with 72mWs worth of energy  0.5 * 0.001F * 12V²
The other 72mWs end as heat on the wires that have 1Ohm of resistance.

If now after capacitor is charged we reverse the polarity of the power supply:
The supply will provide 288mWs and all of that will end up as heat on the wires so 288mWs of heat on wires while capacitor will still have the 72mWs stored from the initial connection.
So since capacitor was already fully charged even if it will be discharged and charged with reverse polarity all energy provided by the source will end up as heat on the wires.
If you disagree with this results we can discuss in more details what happens.
This is for the questions about AC supplies that a few of you asked. So this will be the first cycle.
After this first cycle if power supply keeps switching polarity (AC) then all energy will end up as heat/doing work as capacitor remains with same charged energy as it is discharged and then charged with reverse polarity for each half cycle.

So no energy passes through the capacitor. The current in the wires is due to capacitor being discharged (energy out) and charged (energy in) on each half cycle in case of AC.

[Alex Eisenhut]

What happens to the energy when you charge a capacitor, then move the plates apart?
What about when charging an inductor?

[bsfeechannel]

For me the question is entirely about DC and energy inside vs outside the wire. Nothing to do with switches, transmission lines, capacitors, inductors, transformer theory, antenna theory etc etc.

Which begs the question, is really such a thing as DC? For practical purposes we treat DC as a current that has existed since before the beginning of the universe and will last forever, but in reality whatever the current, it started at some definite point in time in the past and will stop in a foreseeable future. So, what we call DC is in fact just a very wide rectangular pulse. It is essentially transient as anything else, because impermanence seems to be the norm in nature.

If that is so, Heaviside must have thought that, well, if whatever rectangular pulse sent through a transmission line seems to show that energy is conveyed through the space between the wires, why not DC?

[electrodacus]

Which begs the question, is really such a thing as DC? For practical purposes we treat DC as a current that has existed since before the beginning of the universe and will last forever, but in reality whatever the current, it started at some definite point in time in the past and will stop in a foreseeable future. So, what we call DC is in fact just a very wide rectangular pulse. It is essentially transient as anything else, because impermanence seems to be the norm in nature.

If that is so, Heaviside must have thought that, well, if whatever rectangular pulse sent through a transmission line seems to show that energy is conveyed through the space between the wires, why not DC?

Energy will not travel through the space between wires no matter if you have DC, or AC.
It is very easy to see that with DC as the energy storage is not involved.
At power up the energy storage is charged  and at power down the energy storage is discharged. At all times electrical energy travels inside the wires.

[TimFox]

Can energy (or power) at an appropriate frequency propagate down a waveguide, inside the metal walls?

[electrodacus]

What happens to the energy when you charge a capacitor, then move the plates apart?
What about when charging an inductor?

This is not that relevant to current discussion as distance between wires in Derek experiment is not changing.

[TimFox]

If you have a two-plate vacuum-dielectric capacitor, charge it up to a finite voltage, disconnect it, and leave it floating electrically, the charge remains constant when the plates move.
If, mechanically through insulating rods, you pull the plates apart, the capacitance decreases, and the stored energy  E = Q²/(2C) increases.  Therefore, you need to do work by pulling on the rods.
If, the "brake" on the rods releases, the plates will move towards each other and the rods can do work on an external mechanical system.
This is consistent with the well known effect that unlike charges (on the two plates) attract each other:  Left to their own devices, the two plates would attract and crash into each other, and discharge themselves.

[electrodacus]

Can energy (or power) at an appropriate frequency propagate down a waveguide, inside the metal walls?

We are getting way out of subject.
Nothing moves in Derke's experiment.

We have a long transmission line that is charged during transient thus the energy seen through lamp that is in series with the charging capacitors.
Energy flows in capacitors and not through capacitors.  Energy flows through wires and resistors (that are also wires).

[IanB]

We are getting way out of subject.
Nothing moves in Derke's experiment.

We have a long transmission line that is charged during transient thus the energy seen through lamp that is in series with the charging capacitors.
Energy flows in capacitors and not through capacitors.  Energy flows through wires and resistors (that are also wires).

In Derek's experiment, energy or power reached the load before any electrical signals had time to propagate down the wires. Therefore, by experiment, it is proven that energy reached the load by some other path than through the wires.

Whether you like that result or not is irrelevant. The experiment stands. You may wish to come up with your private explanation for that result, and the rest of us may wish to adopt a different explanation. That is OK, but do not expect to persuade anyone to accept your view unless it conforms with the regularly understood laws of physics.

[electrodacus]

In Derek's experiment, energy or power reached the load before any electrical signals had time to propagate down the wires. Therefore, by experiment, it is proven that energy reached the load by some other path than through the wires.

Whether you like that result or not is irrelevant. The experiment stands. You may wish to come up with your private explanation for that result, and the rest of us may wish to adopt a different explanation. That is OK, but do not expect to persuade anyone to accept your view unless it conforms with the regularly understood laws of physics.

That is the exact claim Derek made but it is wrong.
He completely ignores the transmission line energy storage properties.
I never claimed the result is incorrect and I showed the same result based on simulation.
The claim I made is that the conclusion he got that energy travels outside the wire is completely wrong.
What he is basically saying is that electrical energy travels through the 1m air gap and that is not true.

Electrical energy is electrical power integrated over time.
Electrical power is the product of electrical potential (voltage) and electrical current.
Electrical current is defined as flow of electrical charged particles (electrons in this case).

All of you seem to agree there are no electrons flying through that 1m gap from one wire to another.
So all of you agree that there is no electrical current through that 1m air gap.
Many of you mentioned the displacement current but that is a mathematical concept so the equations work not a real current.
At the time Maxwell (mathematician not physicist) has come up with the concept (fictional) displacement current nobody had any clue including Maxwell about the existence of electrons.

All energy in Derek's experiment traveled through wires and that should not be of any surprise to anyone that understands what a transmission line is.
Energy is not flowing through a capacitor but in or out of capacitor (in when charging and out when discharging).

[IanB]

If you write words that agree with the textbooks, then you are wasting your time because we can all read the textbooks.

If you write words that disagree with the textbooks, then you are wasting your time because you won't convince anyone else and apparently you don't wish to learn.

Either way, you are wasting your time posting.

[electrodacus]

If you write words that agree with the textbooks, then you are wasting your time because we can all read the textbooks.

If you write words that disagree with the textbooks, then you are wasting your time because you won't convince anyone else and apparently you don't wish to learn.

Either way, you are wasting your time posting.

Show me the textbooks that say "energy doesn't travel inside the wire" as that is exact quote Derek made.
Why anyone will use wires to transfer energy if they are not needed ?
Also a switch is a capacitor before is being closed so why will you need to close a switch if energy can be transferred through a capacitor.

I do see I'm wasting my time but the alternative is to let humanity fall even more in to idiocracy.

[snarkysparky]

""Many of you mentioned the displacement current but that is a mathematical concept so the equations work not a real current.""

Yes it is a real current.

In a parallel plate capacitor when charge accumulates on one plate the rising electric field ( result of the charge accumulation ) causes charge to leave the other plate (if there is a return path) 

This is exactly the mechanism of displacement current.  It requires a continuous charge buildup between the plates and this is current entering / leaving the plates. 

http://teacher.pas.rochester.edu/phy122/lecture_notes/Chapter35/chapter35.html

[electrodacus]

""Many of you mentioned the displacement current but that is a mathematical concept so the equations work not a real current.""

Yes it is a real current.

In a parallel plate capacitor when charge accumulates on one plate the rising electric field ( result of the charge accumulation ) causes charge to leave the other plate (if there is a return path) 

This is exactly the mechanism of displacement current.  It requires a continuous charge buildup between the plates and this is current entering / leaving the plates. 

http://teacher.pas.rochester.edu/phy122/lecture_notes/Chapter35/chapter35.html

Maxwell had no idea what an electron is ?
The displacement current is fictional (to make observed results fit the math).

If energy was to pass through a capacitor as it does through a wire (with or without resistance) then no energy could ever be stored in a capacitor.
Those 72mJ did not pass through the 1000uF capacitor but in to it and will remain there as stored energy.
That is why when you reverse the voltage supply wires you no longer get anything as it is already charged and all energy delivered by the supply 288mJ will end up dissipated as heat in the wires.
So before capacitor is charged
144mJ = 72mJ on wires as heat + 72mJ in the capacitor as stored energy.
After capacitor is charged there is no energy transfer and if you reverse the supply polarity you have
288mJ = 288mJ on wires as heat and that is all then no more energy flow until you reverse the wires again and then it will again be 288mJ = 288mJ as heat.

[rfeecs]

Those 72mJ did not pass through the 1000uF capacitor but in to it and will remain there as stored energy.

Where in the capacitor is the energy stored?  What is it's physical location?

288mJ will end up dissipated as heat in the wires.

I believe you have said that this heat energy is radiated away in the form of infrared radiation.  What is the difference between infrared radiation and radio waves?

[electrodacus]

Where in the capacitor is the energy stored?  What is it's physical location?

Will that even be relevant or is the important part that energy is stored ?
The electron imbalance between the two plates is the stored energy. You start with equal amount of electrons on both plates and that is a discharged capacitor and in a charged capacitor you will have excess of electrons "parked" in one plate and deficit of electrons in the other plate.
Even when you remove the capacitor from the circuit this imbalance remains and that is how energy is stored.
To discharge you can just short the two plates and electrons form the plate with excess will travel through the wire to the plate with deficit until number of electrons is again equal on both plates. 

I believe you have said that this heat energy is radiated away in the form of infrared radiation.  What is the difference between infrared radiation and radio waves?

That heat is radiated by a resistive device like the wires in this example and a pure resistor is not storing electrical energy.
 

[Naej]

Can energy (or power) at an appropriate frequency propagate down a waveguide, inside the metal walls?

Yes.

[rfeecs]

Where in the capacitor is the energy stored?  What is it's physical location?

I believe you have said that this heat energy is radiated away in the form of infrared radiation.  What is the difference between infrared radiation and radio waves?

You didn't answer either question.  Are you saying there is no physical location?

You didn't answer the second question at all either.

Do you know what a discussion is?

[rfeecs]

Can energy (or power) at an appropriate frequency propagate down a waveguide, inside the metal walls?

Yes.

Is it a trick question?  Inside .. 

[electrodacus]

You didn't answer either question.  Are you saying there is no physical location?

You didn't answer the second question at all either.

Do you know what a discussion is?

  Have I not mentioned electrons that are a physical particle and they have a charge.
It is almost like you are denying that capacitors are an energy storage device.


We are discussing electrical energy not thermal energy.
The infrared photons traveling from one wire to another (or one capacitor plate to another) have nothing to do with electric current.
Yes a few infrared photons from one wire will get to the other wire and slightly heat the other wire but is completely irrelevant for this discussion.
Even if the wire is so hot that it glows in visible light it will not transfer electrical energy to the other wire. It will need to be UV or above in order to displace electrons.
Radio waves are on the other side of the infrared closer to DC.

[rfeecs]

  Have I not mentioned electrons that are a physical particle and they have a charge.
It is almost like you are denying that capacitors are an energy storage device.

So charge equates to energy? 

We are discussing electrical energy not thermal energy.
...
Radio waves are on the other side of the infrared closer to DC.

I sense a contradiction.  Sounds like infrared and radio waves are both in the realm of electrical energy.

[electrodacus]

  Have I not mentioned electrons that are a physical particle and they have a charge.
It is almost like you are denying that capacitors are an energy storage device.

So charge equates to energy? 

We are discussing electrical energy not thermal energy.
...
Radio waves are on the other side of the infrared closer to DC.

I sense a contradiction.  Sounds like infrared and radio waves are both in the realm of electrical energy.

Charge Q=C*V and energy is 0.5 * Q * V


If you have an ideal circuit meaning no resistance then a 12V ideal voltage source charging an 1000uF ideal capacitor will result in 72mJ being transferred from source to capacitor with no loss so there is no infrared.  Total electrical energy in a closed system before charging the capacitor and after is the same and no work was done.
With resistance half of the energy so another 72mJ will be lost as heat so 50% efficiency.
With a more efficient DC-DC circuit to transfer energy you can get to say 90% efficiency so 72mJ in capacitor plus 8mJ wasted as heat.

[SiliconWizard]

Charge held by a capacitor is potential energy.

[Naej]

Can energy (or power) at an appropriate frequency propagate down a waveguide, inside the metal walls?

Yes.

Is it a trick question?  Inside .. 

I think it was, but a correct answer is that current/energy is propagating inside the metal walls. Now the skin depth is typically very small, but it's still inside.

[TimFox]

Can energy (or power) at an appropriate frequency propagate down a waveguide, inside the metal walls?

Yes.

Is it a trick question?  Inside .. 

I think it was, but a correct answer is that current/energy is propagating inside the metal walls. Now the skin depth is typically very small, but it's still inside.

My statement was ambiguous:  I suggested that power propagates down the length of a waveguide, in the air/vacuum that is included in the guide's cross-section, inside the metal walls, in the form of traveling fields.
At those frequencies, the skin depth is very thin, and current does flow within that depth in the walls to establish the boundary conditions.