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Author Topic: Does the capacitor current discharge have the correct interpretation?  (Read 10093 times)

Offline sorincosofret

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Does the capacitor current discharge have the correct interpretation?

Let’s consider a simple circuit made from a DC source, a capacitor and a resistance (fig.1).


Figure 1.

When the switch P is off and the switch K is on, the capacitor charges.
Using actual convention for electric current, an ammeter will registered in circuit a current directed from positive potential to negative potential of DC source. This current charges the capacitor and after a period of time the current stops to flow.
In this process of charging the capacitor plate no 1 become positively charged and plate 2 becomes negatively charged. The potentials of plate capacitor are similar with DC source.
When the capacitor is quite fully charged, the switch K is changed to off and P to on and the discharge current in the circuit is measured.
When this capacitor is discharged, using actual convention, it should have a ,,current” directed  from positive plate to negative plate as in fig. 2-a. This should correspond to a real electron movement from plate 2 to plate 1, through resistance R.
But the sign of this measured current (using actual accepted convention) is opposite to up presented theoretical considerations as indicated in fig. 2-b. It seems that in case of discharge circuit the electrons are flowing from the ,,positive”  plate and arrive to ,, negative” plate of capacitor.
Bullocks as BC said! These electrons do not want to listen of what actual physics says.




Figure 2

The accepted theory gives an explanation for this phenomenon. When the discharge process begins, the sign of the intensity must be minus, because the charge on the capacitor tends to become smaller so:
                                            I = –dQ / dt                                   
A simple question can arise in every inquiring mind. How can I define the current intensity in an external electric circuit as depending on the source quantity of charge?
If instead of a single capacitor a battery of capacitor with a greater (theoretical infinite charge ) is used, how can I define a electric current in a circuit as depending on the charge in battery. How can be measured the quantity of charge in the capacitor?
If the experiment stops before the battery is discharged or if the experimenter does not know the origin of the electric current, what is the meaning of electric current and how can be defined? Why the same current definition does not apply to a DC source?
Let’s suppose we have a set of batteries as DC source. After a period of time playing with K and P, the DC source starts to exhausts. With every capacitor charging, the voltage and the intensity of battery set diminishes, so the charge delivered is smaller. It is necessary to have a special chapter in physics where to clarify when the intensity of current is defined as a quantity of charge passing through a section of circuit and when the current intensity is defined as the quantity of charge lost by de source. After that, new stupid rules regarding the direction of these currents must be established. 
Despite this theoretical debate, the experiment can help to make a little bit order in these bullock things.
I will start with an observation made with another occasion, when the conductivity of solution at a potential lower then value of electrode reaction was tested. Having the following circuit (fig. 3), if for few seconds, the batteries are eliminated from circuit, an opposite and lower current flows into circuit. Of course the current is too small to have some detectable effects and is counted as few micro A in the ammeter.



Figure 3
A greater capacitor, charged at a greater current can give precious information about the nature of discharge electric current.
Let’s consider a variant of the first circuit (fig. 4 ) where the resistance is changed with other and more useful components. In a first trial, this component can be a diode having a resistance as protection in order to prevent a violent discharge and short circuit.



Figure 4.
With this improvement let’s see the reality of phenomena.
In fig. 4-a, with capacitor disconnected, the diode lead to current to pass through circuit. A current is detected into the ammeter.
In a second step (not figured) the P is of and K and L on, thus the capacitor charges.
In fig. 4-b, the third step regard the discharge of current through diode. With presented polarity the diode does not let the current to pass through. A very strange phenomena, because the polarity of capacitor fits with diode polarity and the current should flow into circuit.
If the polarity of diode is changed as in fig. 5, the current is flowing into the circuit.



Figure 5

How is possible to have an electric current in this situation?
The diode is not damaged, but it let the current flow with an inverted source polarity like that foreseen by theory.
 If instead of diode an electrolytic cell is inserted, it can be observed that the effects of currents are opposite as is presented in fig. 6. In electrolytic cell a NaCl solution with phenolphthalein indicator is used.





Figure 6
In 6-a case, the capacitor is disconnected from circuit so the DC source produces the electrolysis of NaCl solution. Besides gas production at both electrodes, due to NaOH generation as secondary reaction at electrode connected at negative pole, the change of transparent solution color to red is very easy observed.
In a second step (not figured), P switch is off and K,L are on and thus the capacitor charges.
After that, as in fig 6-b, the capacitor is discharged on the electrolytic cell.
Depending on capacitor capacity, the operation of charge/discharge must be repeated more times until a visual effect appears.
Despite of known principle of electrochemistry, the negative charge of the capacitor does not produce any color change in the solution. Instead of this, at the electrode connected to positive pole of the capacitor a red color appears.
For any low level schoolboy, is not a big deal to establish the direction of an electric current having this experimental evidence.
The problems appear when this intensity is correlated with actual concept of capacitor charge process. It is impossible to reconcile the effects of capacitor discharge with actual concepts of charge accumulation on capacitor plate.
Therefore in proposed theory there is no charge accumulation on the capacitor charge or in the dielectric. The concept of capacitance as the charge accumulated on the plate (or in dielectric material) is ruled out. More details in the foreseen book.

In order to insure a rapid falling down of the texts in the messages queue, they are locked. In this way all parts are contents. I have a testimonial and the interested readers can search the materials. If there are scientific comments at material, anyone can direct a message to me and I will post the message even is a critique or is unpleasant for me. If there are only bullock as BC said ….. don’t bother to write me.


 

lyner

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what a load of pointless waffle.
Have you ever learned any electrical theory?
You need to get a good textbook and some components and do some measurements.
As I have said before in other contexts: if it's all as wrong as you claim, how does the computer you are using for this work?
Is it all an illusion?
 

Offline BenV

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Sorin - this forum is for science discussion - you are not to use it as a means to publish your ideas.  I'm unlocking this thread so people can discuss what you suggest, whether you like what they have to say or not. 

Please do not attempt to abuse the forum like this again.
 

Offline sorincosofret

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This is not a discussion forum.
It is a place of tolerated trivia when it comes from yours blue blood persons and a place of non tolerated arrogance when I ( a barbarian in your conception) respond to them.
I have made a step suggested by one of your ,,hero". He asked to other forum participants to stop respond me in order to fall in the forgotten aria of this forum.
Therefore I will refuse to make any other comments, if the situation does not change , and you don\t ask to other ,,blue bloods" to have a polite attitude and to make comments with reference from their appreciative ,,good books". I can't put a reference of my ideas because they are no in actual books.
So if you intend to ban me, please do it.
The only advantages for ,,using this forum" instead of any other forum are due to the good tools for text and picture formatting and a relation ,,formal" or ,,non-formal" with Cambridge University.
Look at the last comment as example. Instead of coming with a argument to discussion or to repeat the experiment I am asked how the electronic works. It is like asking Copernicus how planets rotate around Sun, when all people knows their rotation on complicated epicycles etc. They are not able to see at least the difference between reality of a phenomena and a ,,the reality " of a mathematical or physical model.  
I don't wake up at 4 in the morning, and I don't work 10 hours per day ( except my official job) to loose the time and to respond to stupid comments. Anytime I will respond when a real comment or a real suggestion is made to my texts.
Therefore go ahead and make your job.   
 

lyner

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No one is forcing you to write on this forum. You overestimate the worth of your constant stream of published thoughts.
It is just a scatter gun approach with no depth to it. Do you seriously consider that you are capable of rewriting the whole of Science?
Read, listen, think. Then write one sensible thing.
« Last Edit: 09/11/2008 11:00:15 by sophiecentaur »
 

Offline Bored chemist

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This assertion "But the sign of this measured current (using actual accepted convention) is opposite to up presented theoretical considerations as indicated in fig. 2-b. It seems that in case of discharge circuit the electrons are flowing from the ,,positive”  plate and arrive to ,, negative” plate of capacitor. "

is simply not true.

When the cap is charged the electrons pile up on the lower plate of the capacitor. When the key P is closed they travel through the resistor from botom to top. The conventional current flows the other way ie as shown in 2a.
 

lyner

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BenV, perhaps you would invite me to your stately home soon so that our  blue blood families can meet and we can run through the agenda for the next meeting of the Star Chamber. Perhaps we could burn a few heretics (and books) at the same time.
 

lyner

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sorin
Fig 5 of your last post.
The diode is reverse biased. No current  will flow - except, perhaps in your dreams.  You say it is not damaged but, if it conducts that way, it is not a diode. End of your controversial argument.
« Last Edit: 09/11/2008 13:14:04 by sophiecentaur »
 

Offline graham.d

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"When this capacitor is discharged, using actual convention, it should have a ,,current” directed  from positive plate to negative plate as in fig. 2-a. This should correspond to a real electron movement from plate 2 to plate 1, through resistance R.
But the sign of this measured current (using actual accepted convention) is opposite to up presented theoretical considerations as indicated in fig. 2-b. It seems that in case of discharge circuit the electrons are flowing from the ,,positive”  plate and arrive to ,, negative” plate of capacitor."

This statement is wrong. The sign of the current would be, in theory or practice, the same as in fig 2-a. If you did not get this result, your measurement is wrong (you probably have your ammeter the wrong way round). Is that not likely to be a better explanation than the whole of physics is wrong?
 

Offline sorincosofret

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Do we have a rational model for a working capacitor ?
« Reply #9 on: 09/11/2008 14:16:04 »
Do we have a rational model for a working capacitor ?


A capacitor is a device for storing charge. It is usually made up of two plates separated by a thin insulating material known as the dielectric. In a ,,common” capacitor, energy is stored by the removal of charge carriers, more precisely electrons, from one metal plate and depositing them on another. This charge separation creates a potential between the two plates, which can be harnessed in an external circuit. The total energy stored in this fashion is proportional to both the number of charges stored and the potential between the plates. The former is essentially a function of size and the material properties of the plates, while the latter is limited by the dielectric breakdown between the plates. Different materials sandwiched between the plates to separate them result in different energies to be stored. The net charge of the capacitor as a whole remains equal to zero.
The charge stored in a capacitor is proportional to the potential difference between the two plates. For a capacitor with charge Q on the positive plate and -Q on the negative plate, the charge is proportional to the potential:
If the notion of capacitance is introduced (C), it can be calculated as Q = CV
The capacitance is a measure of the amount of charge a capacitor can store;
The energy stored in a capacitor is the same as the work needed to build up the charge on the plates. As the charge increases, the harder it is to add more.
So the energy stored in a capacitor can be thought of as the potential energy stored in the system of positive charges that are separated from the negative charges, much like a stretched spring has potential energy associated with it.
The value predicted by actual theory is: U = QV/2 = Qexp(2)/2C
The presence of this dielectric increases the capacitance of the capacitor compared to when the space between the plates was air or  vacuum.
In order to have a reference for the discussion I think the following link (http://www.physics.upenn.edu/courses/gladney/phys151/lectures/lecture_feb_03_2003.shtml#tth_sEc4.1.1)  is close to the proposed experiments.
In 4.1.4. paragraphs are described the comportment of a air or vacuum capacitor when different  materials are introduced between plates

First, note what happens if we take any single, charged parallel-plate capacitor and insert a slab of conducting material into the space between the plates, but do it such that the conducting material does not touch either plate. The conducting material assumes the charge separation as shown in figure 4.6.




Figure 4.6: Conducting material placed inside a capacitor

…..The solution is to fill the space between the plates with a dielectric material. Dielectrics are non-conductors that are formulated from molecules which either have permanent electric dipole moments or can be induced to have dipole moments in the presence of an external electric field.


These dielectric molecules align partially with any external electric field. They generate a field of their own within the material. This field opposes that of the external field and therefore reduces the magnitude of E within the material. While not quite as effective as a conductor, this material does not conduct charge between the plates of a conductor and still reduces the voltage as a function of charge on the plates. The reduction factor is referred to as the dielectric constant of the material and is usually represented by the letter K. The electric field produced by the charge on the plates of the capacitor remains E0 = q/e0A in any region between the plates which is not occupied by dielectric. In the region which is occupied by dielectric material, the electric field is E = E0/K  with K > 1, i.e. the electric field magnitude is reduced. Since the potential difference between the plates goes as the electric field times the distance, the lower E (and therefore the higher K is), the more charge can be stored on the plates for a given potential difference. There is a very clear description …. charge is stored on the plates, molecules of dielectric are aligned. It is not the case to complicate the present discussion with fringe fields etc.
Experimental part  - Playing with a capacitor
In a first experiment the charge detection on the plate of a capacitor is tested. As was observed in previous messages the home electroscope can detect small quantity of ,,charges” due to a friction of a  polyethylene tube ( circa 1 cm diameter) with a piece of synthetic material or with your hair.
A capacitor, when is almost completely charged, contain a greater quantity of positive charge on a plate and negative on the other plate compared with a simple polyethylene tube. It is not the case to enter into a detailed mathematical description.
First the electroscope is tested with polyethylene tube, keeping in mind that electrostatic experiment are very sensitive to working condition and specially to  humidity. Assuming that electroscope is working well, it can be proceeding with experiment itself.
The capacitor is fully charged, and a capacitor plate contact is approached to electroscope.  Despite a greater quantity of charge on the plate, the electroscope refuses to be charged by influence (no movement of metallic foil in the electroscope). Finally the capacitor plate is set into contact with electroscope metallic part. Again, contrary to kwon laws of electrostatics, the electroscope does not react to the ,,charge presence” from capacitor plate.
The same operations are made to the second capacitor plate with the same result.
Any inquiring mind can ask: Where is deposited the electric charge during the charging capacitor process?

   Second experiment is a repetition of a Benjamin Franklin original experiment. More precisely a home made capacitor is charged, and after that the electrodes are removed and discharged. If uncharged electrodes are attached again to the dielectric, the charge is still present somewhere, because the capacitor give a discharge spark or current.
The experiment was made by Franklin and he concluded that energy is deposited in the dielectric. He didn’t answer how is exactly made. Actual electromagnetism neither explains this fact. I have found a text where is supposed to attribute this energy due to the existence of line of electric filed inside dielectrics.
As it can be observed with an experiment made hundreds years ago, this hypothesis fails, because if the plates are neutral, the line of electric filed inside dielectric does not exists.
In order to remove any doubt regarding the charge ,,existence” in capacitor, the experiment was performed respecting following steps:
1.   The capacitor is charged with a charge Q  in a first step like in fig. 1





2.   The plates are disconnected from dielectric and are put into contact (discharged). It can be ,,admit”  that some charges are remaining on the dielectric plate  as in fig. 2.


3.   Therefore, the plates are fixed again in the original position and again removed and neutralized in order to be sure that no charge are on the dielectric surface.
4.   After this operations, when the capacitor is rebuild and tested, it has a comportment of a charged capacitor.
Even this ,,effect” is known from the beginning of electricity, all ,,good scientific texts”  avoid to present information about it because  it is impossible to imagine a rationale explanation in frame of actual theory.

In proposed theory there is no charge accumulation on the capacitor plate and the electric current is not a charge movement.
« Last Edit: 09/11/2008 14:18:43 by sorincosofret »
 

Offline BenV

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Do we have a rational model for a working capacitor ?
« Reply #10 on: 09/11/2008 14:40:55 »
Does this differ from your other thread about capacitors?
 

Offline sorincosofret

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Do we have a rational model for a working capacitor ?
« Reply #11 on: 09/11/2008 14:53:39 »
It differs: I offer supplementary data about the non existence of charge on plates.
It is not necessary to use a ammeter and to be questioned if the ammeter is working good. In the same time a single and individual experiment with ,,a little bit imagination" can be explained or hidden in any theory. When are more experiments it is more difficult to do that.
 

lyner

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Quote
Is that not likely to be a better explanation than the whole of physics is wrong?
I think sorin reckons he is in with a chance.
 

lyner

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Do we have a rational model for a working capacitor ?
« Reply #13 on: 09/11/2008 15:16:40 »
This an old chestnut - If you 'just take the plates away' you are actually doing work and you are disturbing the whole experiment.
For a capacitor with no dielectric, because Q=CV, the PD between the plates will go up as you separate them - work done - because the Capacity decreases. There is still the same charge on each plate as before.
IF there is a dielectric involved then taking the plates away still leaves the dielectric polarised. The majority of the energy stored in a practical capacitor is actually in this dielectric polarisation.
Replacing the original plates with another, fresh, pair will produce a situation which is pretty much indistinguishable from the original.

You would have found out about all this if you had done some reading around in the books which you seem to ridicule so much.
You have not a cat's chance in hell of finding something 'wrong' with this area of classical circuit theory. It's not 'blue blood' or Chauvinism at work - it's just very well established Science.
Read, listen and learn.
Or perhaps this is, in fact, a bizarre way of learning for you.
« Last Edit: 09/11/2008 22:09:02 by sophiecentaur »
 

Offline Bored chemist

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Quote
Is that not likely to be a better explanation than the whole of physics is wrong?
I think sorin reckons he is in with a chance.
Close,
Sorin doesn't think physics is in with a chance up against his mighty intellect.
BTW, has anyone else noticed that spell checing posts like this leads to the option "Ignore all" for every instance of "Sorin".
Tempting isn't it?
 

Offline BenV

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I have merged the 2 threads about capacitors - I couldn't determine enough difference between the two and, as sorin said, the second one contained supplementary info.
 

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