Capacitors dielectric

[Chassis]

Good day. I'm trieng to find out how current can flow through a capacitors dielectric .when does it flow through and when does it not. can somone please make it very clear to me please.I'm that type of person that won't rest untill I get it right.

 

[hevans1944]

A DC current cannot flow through a capacitor's dielectric. By definition, a dielectric is an insulator for DC current. An AC current can flow in a capacitor, with some impedance to the flow, that is a function of the AC frequency and the capacitance. The higher the frequency, or the more the capacitance, the more easily current can flow.

 

[Chassis]

Thanks a lot Hevans.so tell me,how does the bulb light still lights up when its connected with a battery (DC) circuit via a capacitor.it stil lights up while the circuit is close,and also lights up when the circuit is open (capacitor discharging)how does the current find its way through the insulation (dielectric)?.

 

[BobK]

Current flows while a capacitor is charging or discharging. That is why you see the bulb light up. Current does not flow through a capacitor, it flows into the capacitor on one side and out of the capacitor on the other side until the capacitor is charged to the voltage that is driving it, then the current stops since the capacitor cannot accept any more charge.

Bob

 

[hevans1944]

... so tell me,how does the bulb light still lights up when its connected with a battery (DC) circuit via a capacitor.it stil lights up while the circuit is close,and also lights up when the circuit is open (capacitor discharging)how does the current find its way through the insulation (dielectric)?.

Please sketch and upload to the forum a circuit diagram that shows what you are talking about. Your question doesn't make any sense to me. How can the bulb light up when the circuit is open? How is the capacitor discharging when the circuit is open? What is the capacitor discharging into? How did the capacitor get charged in the first place?

Current doesn't "find its way through the insulation (dielectric)"... ever. Current is what it is, and it has no volition to find its way through anything. Current doesn't "want" to "seek" the path of least resistance. Nature does not abhor a vacuum. Electricity is not to be fully understood by simplistic analogies or hand-waving explanations. From whence comes your questions?

 

[Chassis]

Hi hevans. I am sorry for the little and poor info. I think I am confused with the the way the circuit gets drawn. are the leads of the capacitor attached together alowing current to flow into it? please view the 2nd image how (DC) flows into one side of the capacitor and out on the other side of the capacitor.

 

[davenn]

This is a very different situation to what you were initially describing in your first post

please view the 2nd image how (DC) flows into one side of the capacitor and out on the other side of the capacitor.

it, doesn't, electrons flow in the negative side of the capacitor, from the negative side of the battery, till its charged ( energised is a better description). Then the cap is removed from the battery and is connected to the LED. Current ( electrons) then flow back out of the negative side of the capacitor and through the LED lighting it up till the capacitor discharges

The current isn't flowing through the capacitor, it is flowing in and out of the same terminal of the capacitor

Dave

 

[Ratch]

Good day. I'm trieng to find out how current can flow through a capacitors dielectric .when does it flow through and when does it not. can somone please make it very clear to me please.I'm that type of person that won't rest untill I get it right.

AC or DC never passes through an ideal capacitor. If it does, the capacitor is defective and leaky. A perfect dielectric is a perfect insulator. A DC will accumulate a charge on one capacitor plate and deplete the charge on the opposite plate. This will enable a transient current to exist through the leads of the cap until it is energized up to the applied voltage. An AC will also accumulate a charge until the applied voltage changes polarity and switches the plates to accumulate/deplete charge. Again, at no time does charge pass through the capacitor, even though a ammeter will show a current exists in the cap leads. This is just the accumulation and depletion current.

Ratch

 

[Chassis]

Ratch ! your reply makes it very clear to me,I had a totally different image of how this works.big thanks to you and the others

 

[Laplace]

AC or DC never passes through an ideal capacitor.

Why would that be a useful concept for applying Kirchoff's Current Law in a circuit with a capacitor? If current is flowing into one side of a capacitor and an equal current is flowing out the other side of the capacitor, then can't we just pretend that current is flowing through the capacitor? What if there were a 'mystery component' with two leads, and current flowed into one lead and an equal current always flowed out the other lead, wouldn't it be correct to say that current flowed through the component? Why would we change that convention if it were known that the mystery component was a capacitor?

 

[davenn]

What if there were a 'mystery component' with two leads, and current flowed into one lead and an equal current always flowed out the other lead, wouldn't it be correct to say that current flowed through the component? Why would we change that convention if it were known that the mystery component was a capacitor?

this became a long heated discussion several months ago
Again ... current only "APPEARS" to flow through a cap
its flows in and out of each leg but not between legs, else it's no longer a capacitor

 

[Laplace]

current only "APPEARS" to flow through a cap

So does that mean we can analyze a capacitor circuit with KVL and have the loop currents 'appear' to flow through the capacitor components?

 

[davenn]

The original post has been answered by several people already
KLV doesn't need to be brought up to answer the OP
I'm not going to let the thread degrade into another long drawn argument
that goes on for a dozen pages of "he said - she said"

Thread closed

Dave