A Pedantic Question

[nsaspook]

Sometimes simple questions have complex answers. What's happening 'inside' a capacitor is outside the normal physical movement of things we see in daily life so it's easy just to say it acts like a 'duck' and move on but does that really provide information that will be useful later in understanding advanced circuits or electronic principles.

 

[tvtech]

tvtech,

Seems to me you're the only one trying to be clever. You have everyone figured out and classified. You know which are the clever braggarts, with something to prove, and which are the non-clever humble saints. The clever psychologist you seem to be purporting yourself to be, identifying who is the good guy and who is the bad guy.

Strange that anonymous people would be so worried about trying to prove their cleverness. Yes, why would they be motivated by the enjoyment of trying to help other people, or by enjoyment of discussing anything related to the subjects they are passionate about to learn more and seek out alternative points of view to help their thinking, or by the desire to correct what they view to be a mistake that might mislead others, or by the desire to defend an author that is criticized and is not here to defend himself.

Hey, no one learns by shutting up and sitting in the corner just because you will be annoyed by their talking. So if you are bothered, then you leave or ignore people. Don't try to intimidate others into behaving the way you think is correct. The moderators can handle anything that goes out of bounds of what is appropriate. Leave it to them.

Just me too,
Steve

LOL Steve

Honestly not aimed at you. Aimed at another individual here who insists on complicating simple things...

Lets call this individual the "hopelessly pedantic one".

You could teach me all day long. And I would learn. And not not fall asleep or question...capice??

It's a long story

Regards,
tvtech

 

[shortbus=]

One mans pedantic, is another mans troll.

 

[tcmtech]

One mans pedantic, is another mans troll.

You gave me my giggle for the day!

From my perspective I haven't seen any trolls here.

Pedantic is fine with me. Just don't declare ones self irrefutable over a poorly supported opinion based on conclusions derived from highly biased pseudo science.

That's when I go troll hunting.

 

[Mr RB]

...
Internally, we could have 50 people going right through as you noted but we could have the other 50 coming from the train that stops at the station.
...

Totally irrelevant to the guy designing the subway system, he needs to know how many people "through" the station per day, and "through" is the correct technical term.

...
With the capacitor, we want to say that the charge entering one side stays there while free charge from the other side moves out of that side. So we have added to one plate and taken away from the other plate but no charge actually moved through the cap.
...

Who is "we"? I don't want to say that, I think it is nitpicking and a complete waste of time. In electronics we need to use the capacitor in a circuit, and need to know its capacitance, and peak voltage and ESR issues etc. What happens inside it does not matter in any way unless maybe you are a physicist. With my students I teach the electronics truth; AC current can flow through a capacitor, DC current cannot (and I add the technically superfluous word current to AC and DC as people generally use AC and DC to mean voltage).

...
Does this make sense to you as to why we talk about this from time to time now?

No. Actually I think it is a stupid meaningless argument whcih has little to no use and confuses beginners who need to know the facts; ie if there is a complete circuit with a cap and an ammeter and there is 1A AC current then there is 1A AC current going through the cap.

Or how about a Japanese subway with a rubber wall in the middle. It's already full so when you cram another 100 people in one door 100 people get forced out the one on the other side? Sorry, couldn't resist.

Please, even though this IS off-topic, let's not start on the Japanese and their rubber fetishes.

...
And, most importantly, kids asking simple questions don't run away from here because they are Witness to all their simple questions turned into a thesis.

You know what I think John....ETO should put Moderation on Threads where simple answers are required.
...

Excellent! Simple answers. This is electronics, the thing beginners need to know is that AC flows through a cap, DC does not. Anything else dissolves into "clever wars" about the meaning of the word "through" or corrupting the base issue with nitpicking about EXACTLY what happens inside a cap, who cares?

It DOES NOT help educate anyone in electronics learn about how to use that cap.

It is as stupid an argument as nitpickers insisting that REAL current flow is electron flow and insisting that beginners talk in "electron flow" terminology and start drawing their diodes with the arrows the other way around! Who cares which way electron flow occurs? We have a standard which is taught to beginners that "current" flows from + to -, and that is the best way to teach it, regardless of how much that might annoy pedantic OCD nitpickers.

In electronics, current flows from + to -. In electronics, AC current flows through a cap. In electronics, we use the term "Alternating Current" to actually describe voltage. Now get over it.

 

[MrAl]

Hi MrRB,


Well you are arguing with me about something telling me that 'your' single view is better than the 'dual' view where we 'know' that there are two different approaches. It doesnt matter if one view works better for most applications because we want to know BOTH views. Maybe you are satisfied with one view, and that's fine, but you cant tell me that i am not allowed to question or think about that second view, and surely you cant tell me that i cant talk about it can you? It's not a topic for a beginner and i never said it was, but we are not beginners are we, so we can talk about it.

When i said that "we" want to say that charge enters one side and moves out of the other side i mean that is accepted theory about charge accumulation and depletion.

AC current is not really flowing 'through' a capacitor, that's what the point was, but you can still measure current going in and current going out. We can also apply a DC current, and again see current going in and going out (for example a current source).

When you say AC current do you mean sinusoidal current? Well we can examine that in one half cycle to tell what is going on, we dont really need it to vary over many cycles.

Stupid meaningless arugument? I dont think so. Stupid to you yes, but not to everyone. People want to know the true physics of things sometimes. The two slit experiment is another. It's part of the physics that could help explain something else in the future. Some minds want to know, others dont. You dont, some others here dont, i do and Maxwell did too.

When i kid asks a question in a new thread that is a differernt story. Here that did not happen so we are not replying to a kid or newbie but someone who has much more understanding of nature already.

 

[Ratchit]

Mr RB,

With my students I teach the electronics truth; AC current can flow through a capacitor, DC current cannot

Do your students ask how current can exist through a cap when the dielectric is an insulator? What about the professor referenced by nsaspook in post #37 of this thread, who specifically says that current does not exist through a cap?

DC current cannot (and I add the technically superfluous word current to AC and DC as people generally use AC and DC to mean voltage).

I always thought DC meant "defined continuous" and AC meant "alternating cycle". Both current and voltage can have this property.

It is as stupid an argument as nitpickers insisting that REAL current flow is electron flow and insisting that beginners talk in "electron flow" terminology and start drawing their diodes with the arrows the other way around!

Yes, it is stupid to define current direction by the polarity of the charge carriers. After all, electrons are not the only charge carriers. There are semiconductor holes and positive ions in electrochemical reactions that have the opposite current direction. It is best to assume mathematically that all charge carriers flow from positive to negative. Then, if their true direction is needed to be known, reverse the direction of the negative charge carriers.

Who cares which way electron flow occurs?

It becomes important in bipolar devices where different polarities of charge carriers exist, such as holes and electrons.

In electronics, AC current flows through a cap.

How? When the dielectric is a insulator.

In electronics, we use the term "Alternating Current" to actually describe voltage. Now get over it.

"Alternating cycle" applies to both current and voltage.

Ratch

 

[ericgibbs]

I always thought DC meant "defined continuous" and AC meant "alternating cycle". Both current and voltage can have this property

Morning Ratch,

DC has always been used to mean Direct Current, not ' defined continuous'.

AC was defined as Alternating Current, not Alternating 'Cycle'

Why the early engineers chose these definitions, who knows, but it works for me...

Why you keep trying to redefine well used terminology beggars belief, it must confuse the hell out of wannabes who are trying to understand the subject and heaven help any interviewee who uses terms like 'defined continuous' and 'alternating cycle' during an interview.

One of my ETO peers summarised it up well by saying this type of argument is like asking.

How many angels can dance on the head of a pin.!

Eric

 

[dougy83]

How many angels can dance on the head of a pin.!

So how would you devise an experiment to prove the answer to this question?

 

[MrAl]

Hi Eric,

I have to disagree about the angels and pin thing for this particular questionable thing, because laboratories have in the past taken up this venture. We are not the only ones to ask this.

How about this simple argument:

We have a capactor with 2 units of charge on the left plate, and 2 units of charge on the right plate. Using a current source, we push 1 more unit of charge onto the right plate and pull 1 unit off of the left plate, so that leaves 1 unit on the left plate and 3 units on the right plate, then we remove the current source. The cap overall charge is still 4 units, but now we see a potential difference across the cap due to an imbalance of charge.
And all that took place without ever having to move even a tiny amount of charge THROUGH the cap and all charge can be accounted for.

Now lets look at what happens if we let 1 unit pass THOUGH the cap...
2 units on the left, 2 on the right, using current source push one more onto the right plate, pull one off the left plate, let one pass THROUGH the cap vacuum.
Since we had 2 on the right to start and we added 1, we would have a total of 3 but this time we let 1 pass through the cap from right to left. That one had to land on the left plate. So after we remove the current source this time we still have 2 units on the right plate. Now we also removed one from the left plate but we also added one from the unit that got THROUGH the cap vacuum, so we have a total of 2 on the left plate now.
So in the end this time we have 2 on the left and 2 on the right, hence we have no difference in charge distribution and therefore we can not have a voltage difference across the cap this time.

So compare these two with what is observed in nature and we find that the first experiment works and the second one fails. The first one works because we measure a voltage across the cap in the end, and the second one fails because we do NOT measure a voltage across the cap after the application and subsequent removal of the current source.


One man's pedantic is another man's raconteur

 

[ericgibbs]

So how would you devise an experiment to prove the answer to this question?

hi Dougy,

You know as well as I, that an experiment to attempt prove a such a question as this would be a complete waste of time.

That type of question ie: How many angels can dance on the head of a pin.! is often asked by members who IMO just want to have a medium for trolling.

E

 

[tcmtech]

So why are the properties of electrostatic charge being ignored here?

To me this whole argument is like saying that one conductor can not make current flow in a second inductor because they are separated by a dielectric material. Well yes that argument would be true provided you ignore inductive coupling through electromagnetic interactions.

So does AC current flow through a capacitor? Yes it does and it does it using other principles of electrodynamic interactions besides direct conduction. Electron charge states of each plate change thus creating current flow.

 

[ericgibbs]

morning Al,

For all practical purposes an AC [alternating current ] Source connected to the plates of Capacitor will result in an AC current flowing in the loop circuit of the Source and the Capacitor.

We all 'know' that the electrons will not conduct/flow thru the dielectric of the capacitor.

E

 

[bryan1]

I was going to to stay out of this but temptation was well........

Years ago when I was playing with F&P washing machine motors for wind generators I decided to try a couple of 400volt 470uf caps soldered back to back to make them non polarized and put then in series with the 3 AC leads of the wind genny.

When the genny was doing 250 rpm without the caps the output was around 5-6 amps

When the Genny had the caps in series @250 rpm the current was 10-11 amps

A so called mate came up to my farm and saw the results then went off on his own bent claiming fame and now it is standard practice to increase the current on F&P wind gennies......

So does current flow thru a cap any naysayers just look what I wrote above....... Caps not only flow thru current they can increase the current.........

 

[nsaspook]

Charge/current is fundamental when EM energy interacts with the plates but it's not a requirement for the transmission of EM energy across the plates of a capacitor. Saying it's so (current flow through a capacitor) is a sleight of hand trick that satisfies but some want to know how the trick is done.

**broken link removed**

 

[Ratchit]

Eric,

DC has always been used to mean Direct Current, not ' defined continuous'.

AC was defined as Alternating Current, not Alternating 'Cycle'

Why the early engineers chose these definitions, who knows, but it works for me...

If you refer to a sinusoidal voltage as AC, meaning "alternating current", then it could be thought of as "alternating confusion".

If you refer to a battery voltage as DC, meaning "direct current", then it could be thought of as "direct contradiction".

Ratch

 

[ericgibbs]

Eric,



If you refer to a sinusoidal voltage as AC, meaning "alternating current", then it could be thought of as "alternating confusion".

If you refer to a battery voltage as DC, meaning "direct current", then it could be thought of as "direct contradiction".

Ratch

Very funny Ratch,
but I dont see any mention of voltage in my post, perhaps quoting members posts out of context is your way of trying to add another Angel onto the pinhead.?

E

 

[JimB]

Just to toss an extra little hand grenade into the room...

... does this current which may or may not flow through a capacitor, obey Ohms Law?

Another topic which is sometimes debated to absurdity.

JimB

 

[Ratchit]

JimB,

Just to toss an extra little hand grenade into the room...

... does this current which may or may not flow through a capacitor, obey Ohms Law?

Grenade fizzled. Ohm's law refers to a property of a material. Current is not a material.

Ratch

 

[JimB]

Grenade fizzled. Ohm's law refers to a property of a material. Current is not a material.

Last time I looked capacitors were made of material.

JimB