A charged capacitor restricts current flow due to the insulating dielectric between its plates, preventing conduction current from passing through. While charging, current flows into one plate and out of the other, creating a displacement current related to the changing electric field. Once the voltage stabilizes, the current ceases because the charge on the capacitor remains constant, as described by the equation I = C dV/dt. Thus, in a steady state, no current flows across the dielectric, even though current circulates in the external circuit.
PREREQUISITESElectrical engineers, physics students, and anyone interested in understanding capacitor behavior in circuits, particularly in relation to current flow and electric fields.
But while charging, doesn't current flow in the circuit?phyzguy said:A capacitor is two conductors separated by an insulator. In the DC case, there is no path for the current to flow across the insulator.
ubergewehr273 said:But while charging, doesn't current flow in the circuit?
Of course that's true but then how would you explain the flow of current through a circuit as a whole then? In the charged cased, current doesn't flow in the circuit and of course,not between the capacitor plates. While charging, current flows through the circuit but not between the capacitor plates. But as such, how does a capacitor simply block the flow of current when completely charged? And how does current flow through the entire circuit while charging as there is a insulating medium in the path of the current (in the capacitor) ?phyzguy said:Yes, but the situation is a little bit subtle. When the capacitor is charging, a current I is flowing into one side of the capacitor, and the same current I is flowing out the other side. So, from the outside, it looks like a current I is flowing through the capacitor. But that isn't what is happening. The current I flowing into one side is being stored as charge on one capacitor plate, and a current I is leaving the other capacitor plate causing it to build up an opposite charge. So in no case does current flow across the insulating gap between the two conductors. Do you see?
ubergewehr273 said:And how does current flow through the entire circuit while charging as there is a insulating medium in the path of the current (in the capacitor) ?
ubergewehr273 said:While charging, current flows through the circuit but not between the capacitor plates.
Yes but my doubt is exactly how does current flow through the circuit when a capacitor is connected to it ? Current flows through the external circuit, but when I consider the capacitor charge accumulation takes place on the respective plates simultaneously. I am unclear with the idea of the capacitor allowing no current to pass when both the plates of the capacitor have maximum charge accumulated on them.Lord Jestocost said:There is no conduction current flowing between the capacitor plates because there aren't - in the ideal case - mobile charged carriers. However, as long as the charging progresses, there "flows" - so to speak - a displacement current inside the capacitor which is related to the temporal change of the electric field between the capacitor plates.
ubergewehr273 said:Yes but my doubt is exactly how does current flow through the circuit when a capacitor is connected to it ? Current flows through the external circuit, but when I consider the capacitor charge accumulation takes place on the respective plates simultaneously. I am unclear with the idea of the capacitor allowing no current to pass when both the plates of the capacitor have maximum charge accumulated on them.
I don't find the explanation in sync with the doubt that I have. :(phyzguy said:I don't know how to explain any more clearly. What about my explanation do you not understand or disagree with?
ubergewehr273 said:I don't find the explanation in sync with the doubt that I have. :(
This is my doubt.ubergewehr273 said:I am unclear with the idea of the capacitor allowing no current to pass when both the plates of the capacitor have maximum charge accumulated on them.
Lets put it this way, obviously current flows in the circuit and till that time there is a varying electric field inside the capacitor. Now I am not sure why does the flow of current stop when the electric field becomes constant inside the capacitor.phyzguy said:Can you state your doubt more clearly? If your question is "How does current flow across the dielectric cap?", then the answer is either:
(1) It doesn't. It stops at the dielectric gap and new current starts on the other side of the gap.
(2) The physical current is converted to a displacement current and the displacement current flows across the gap.
I think I'm a bit hazy about it.Dale said:Have you been introduced to the concept of the “displacement current”?
Ok, thanks a lot.phyzguy said:Current only flows into (or through) the capacitor when the voltage is changing. When the voltage is constant, then the charge on the capacitor doesn't change, so the current (which is dQ/dt) is zero. This is why the current through a capacitor is given by I = C dV/dt.
ubergewehr273 said:Lets put it this way, obviously current flows in the circuit and till that time there is a varying electric field inside the capacitor. Now I am not sure why does the flow of current stop when the electric field becomes constant inside the capacitor.
ubergewehr273 said:Ok, thanks a lot.
ubergewehr273 said:Case a of a charged capacitor.