why can the capacitor be charged by a battery (DC)

[zxcvb]

Hey, guys!

I'm so confused that why the capacitor is DC blocking, but the battery (DC) can indeed charge the capacitor?

I've never thought about this until I read it in the book recently. I really have no idea about it.

I've read some articles, but I still don't know how it works.

If anyone knows why this happens, please tell me something about it.

Any ideas would be greatly appreciated.

 

[gyraf]

hi zxcvb,

It's not entirely clear why you are asking here, in stead of reading the literally thousands of intro guides available - or the many many youtube vids on the subject.

Reason for me being slightly reserved is that your posts' embedded weblinks marks you as a very possible spammer, who at the same time seeem to know close to nothing about the substance of what this group is about

If you're genuine interested-but-unknowing, please do continue - but please try not to use links in posts (or anywhere else) unless absolutely necessary

All the best,
Jakob E.
Mod.

 

[abbey road d enfer]

I'm so confused that why the capacitor is DC blocking, but the battery (DC) can indeed charge the capacitor?

Actually current passes through a capacitor, until it has developed such a voltage that no current is generated (that is when the capacitor is charge at a voltage that exactly compenstes the voltage which it is presented to).
When a battery meets a capacitor, there is a brief current surge, that charges the capacitor at the same voltage as the battery, and current ceases to flow.
When the capacitor is charged through a resistor, the surge is smaller and lasts longer, until the capacitor is fully charged, and current drops to zero.

 

[Bo Deadly]

When teh capacitor is charged through a resistor, teh surge is smaller and lasts longer, until the capacitor is fully charged, and current drops to zero.

You could say the same thing about a battery. A battery is exactly the same as a capacitor. It just has a much larger capacity. It's so large that it seems to the untrained eye to be a source of DC. But in truth current does not actually pass through a capacitor or a battery. They both just build up a charge across some kind of barrier. All current in / out is only used to charge up / down. Once that charge reaches equilibrium, the current stops.

 

[Rob Flinn]

Actually current passes through a capacitor.

The way I understood it was that current is a flow of electrons & that they don't actually pass through the capacitor. The current that does flow charges the plates in the capacitor, but in the theoretical perfect capacitor no current flows throigh it, which is why when the capacitor is fully charged no more current flows.

 

[abbey road d enfer]

You could say the same thing about a battery. A battery is exactly the same as a capacitor. It just has a much larger capacity. It's so large that it seems to the untrained eye to be a source of DC. But in truth current does not actually pass through a capacitor or a battery. They both just build up a charge across some kind of barrier. All current in / out is only used to charge up / down. Once that charge reaches equilibrium, the current stops.

The way I understood it was that current is a flow of electrons & that they don't actually pass through the capacitor. The current that does flow charges the plates in the capacitor, but in the theoretical perfect capacitor no current flows throigh it, which is why when the capacitor is fully charged no more current flows.

Roll over Kirchoff!

 

[moamps]

You could say the same thing about a battery. A battery is exactly the same as a capacitor. It just has a much larger capacity. It's so large that it seems to the untrained eye to be a source of DC. But in truth current does not actually pass through a capacitor or a battery. They both just build up a charge across some kind of barrier. All current in / out is only used to charge up / down. Once that charge reaches equilibrium, the current stops.

Come on. Batteries do not work on the same principle as capacitors.

 

[ruffrecords]

Roll over Kirchoff!

No Kirchoff law is violated. When a cap charges all that happens is the electrons gather on one plate of the cap until the charge equals the applied emf. At all times during the process both Kirchoff's laws hold true.

Cheers

IAn

 

[abbey road d enfer]

No Kirchoff law is violated. When a cap charges all that happens is the electrons gather on one plate of the cap until the charge equals the applied emf. At all times during the process both Kirchoff's laws hold true.

That's what I meant.
Those two assertions would make Kirchoff roll over in his tomb.

 

[JohnRoberts]

bot?

 

[Rob Flinn]

I guess the give away is the fact that a capacitor is 2 conductors separated by an insulator ..............

 

[Bo Deadly]

It is not wrong to say that current flows "through" a capacitor. Current flowing in one terminal does indeed match the current flowing out the other. So no laws of physics have been broken. But it is an AC current and not a DC current and the question asked about a capacitor blocking DC. Which it does. The electrons flowing into one terminal are not the electrons flowing out the other. So perhaps it would be more accurate to say that electrons do not flow "through" a capacitor. At least the electrons flowing into it are not the same electrons flowing out the other side. They are just accumulating along the capacitor boundary (AKA charging up) proportional to the applied voltage.

Imagine a capacitor with 0V across it and at equilibrium such that no current is flowing. Then a voltage is applied. Instantaneously the capacitor is no longer at equilibrium. The voltage across it will attract electrons to flow into one terminal while simultaneously and equally repelling electrons to flow out of the other terminal.

 

[Rob Flinn]

It is not wrong to say that current flows "through" a capacitor.

. So perhaps it would be more accurate to say that electrons do not flow "through" a capacitor.

Since current is electron flow & the same electrons don't go into one terminal of the cap & out of the other under a.c or d.c circumstances there is no current flowing through the cap. I agree that in a.c circumstances it has the appearance of current flow, but ignoring leakage there is still no current flowing through the component because in the ideal theoretical model current doesn't flow through an insulator. It is just the cap charging and discharging.

 

[Bo Deadly]

Since current is electron flow & the same electrons don't go into one terminal of the cap & out of the other under a.c or d.c circumstances there is no current flowing through the cap.

As a pedantic detail I would agree. Current does not flow through a capacitor just as we would say current does not flow "through" a transformer.

 

[Winston OBoogie]

I think John & Jakob are correct in that this was a spam bot letting off a wee stink bomb and then scurrying for cover.
Save your energy folks

 

[abbey road d enfer]

The electrons flowing into one terminal are not the electrons flowing out the other.

That is the case with any conducting material. The electrons move incredibly slow compared to the "speed of electricity". Like in a recirculation ball screw, the movement is transmitted almost immediately, but the balls may take a long time for a complete round.

So perhaps it would be more accurate to say that electrons do not flow "through" a capacitor.

Did I mention electrons? No.
Current flows through a capacitor, the electrons may or may not.

 

[abbey road d enfer]

Since current is electron flow & the same electrons don't go into one terminal of the cap & out of the other under a.c or d.c circumstances there is no current flowing through the cap. I agree that in a.c circumstances it has the appearance of current flow, but ignoring leakage there is still no current flowing through the component because in the ideal theoretical model current doesn't flow through an insulator. It is just the cap charging and discharging.

I believe you should revise your notions of electrostatics and how electrostatic charges react with each other.
If there was no current through a capacitor, how could a voltage develop in a load?

 

[abbey road d enfer]

I think John & Jakob are correct in that this was a spam bot letting off a wee stink bomb and then scurrying for cover.
Save your energy folks

It's just unfortunate that such a question, legit or not, brings those wrong answers. I believe it deserves being corrected.

 

[abbey road d enfer]

I guess the give away is the fact that a capacitor is 2 conductors separated by an insulator ..............

Then how can current flow in a vacuum tube?

 

[moamps]

...... Kirchhoff....

I'm just wondering what the conclusion of this board is, is the current going through the capacitor or not?