simple but complicated to understand

[vijaybaliga]

we all know that in capacitor there will be no ay physical connection between the two electrodes of the capacitor ,and the charge is stored between these electrodes during charging , so with out any physical connection how these charge is transferred from one plate to the another plate during the discharge :?:?:?:?

 

[Smart $]

we all know that in capacitor there will be no ay physical connection between the two electrodes of the capacitor ,and the charge is stored between these electrodes during charging , so with out any physical connection how these charge is transferred from one plate to the another plate during the discharge :?:?:?:?

In the same manner as charging, but in the opposite direction.

In charging, the electric charges from one "plate" are transferred to the other (likely not the same electrons). The process is simply reversed during discharging.

There is no direct electrical connection between plates, but an indirect connection must be present. You have to remember that in order for current (of electric charges) to flow, there must be a loop. Between the plates is just one section of the loop in both charging and discharging.

Welcome!!!

 

[SAC]

There must be an electric field applied, and a path for charge to flow, in order to move charge from one plate to the other.

As an analogy, picture a plastic cube half full of water and open on top. There is barrier down the middle, so that each side is separated from the other. There is a plastic tube that comes out of the bottom of each side, and goes to each side of a bi-directional pump. The pump can move water from one side to the other. If the water level is the same, there isn't any energy in the system. If the pump moves water from one side to the other, there is now stored energy (the force from gravity that creates pressure on one side) that can move the water back to the other side if the pump shuts off (assuming the pump is "leaky" when turned off). Water moves from one side to the other, but doesn't go through the barrier in the middle.

This is "sort of" what happens with a capacitor - though obviously the physics are different since we are talking about electromagnetic fields instead of gravity. Instead of water it is charged particles, and instead of tubes there are wires, and instead of a pump there is a voltage source. At first the charged particles are evenly distributed on both plates of the capacitor. The voltage source provides an electric field that moves the charged particles from one plate to the other. One plate becomes more positive, and the other, more negative. The difference in charge on the two plates causes an electric field to form between them. The charged particles are moved until the electric field across the barrier between the two plates is equal and opposite that which is being applied by the voltage source. Now if the voltage source turns off (but again, is "leaky" when off), the electric field across the plates of the capacitor is such that it provides a force on the charged particles that will move them back to the other side, until the charge on the two plates is balanced again.

 

[kwired]

There must be an electric field applied, and a path for charge to flow, in order to move charge from one plate to the other.

As an analogy, picture a plastic cube half full of water and open on top. There is barrier down the middle, so that each side is separated from the other. There is a plastic tube that comes out of the bottom of each side, and goes to each side of a bi-directional pump. The pump can move water from one side to the other. If the water level is the same, there isn't any energy in the system. If the pump moves water from one side to the other, there is now stored energy (the force from gravity that creates pressure on one side) that can move the water back to the other side if the pump shuts off (assuming the pump is "leaky" when turned off). Water moves from one side to the other, but doesn't go through the barrier in the middle.

This is "sort of" what happens with a capacitor - though obviously the physics are different since we are talking about electromagnetic fields instead of gravity. Instead of water it is charged particles, and instead of tubes there are wires, and instead of a pump there is a voltage source. At first the charged particles are evenly distributed on both plates of the capacitor. The voltage source provides an electric field that moves the charged particles from one plate to the other. One plate becomes more positive, and the other, more negative. The difference in charge on the two plates causes an electric field to form between them. The charged particles are moved until the electric field across the barrier between the two plates is equal and opposite that which is being applied by the voltage source. Now if the voltage source turns off (but again, is "leaky" when off), the electric field across the plates of the capacitor is such that it provides a force on the charged particles that will move them back to the other side, until the charge on the two plates is balanced again.

The leaking pump when turned off is analogus to what happens when a discharge resistor is installed across the capacitor.

 

[charlie b]

Let's get one thing clear here. Charge does not, Not, NOT move from one plate to the other (i.e., it does not jump across the insulation medium that separates the two plates). :happysad: Are we on board with that statement? :happyyes: I will assume so, and I will proceed.

The simplest explanation of how a capacitor works, and in particular how it is able to allow current to flow across the apparently infinite gap betweeen the plates, starts with recalling that opposite charges attract, and that like charges repel. As negative charge starts to accumulate on one plate, consider the viewpoint of an electron on the opposite plate. It is negative, and there is a growing negative charge across the gap. The electron on the second plate will therefore feel a push, simply because it possesses the same type of charge as the charge on the first plate. So the electron on the second plate begins to move. Now, from the viewpoint of a person watching the wire that is attached to the second plate, it appears that negative charge is in motion within that wire, and that is the definition of current.

If you connect a capacitor to a battery (i.e., a DC source), then negative charge will start to build up on one plate, and electrons will start to leave the other plate. This goes on for a while, but has to come to an end at some point, since there is a limited amount of electrons on the second plate, and since there is no process to bring any electrons back to the second plate. Thus, current will flow for a while, then current will stop flowing. In the "steady state" or "equilibrium" condition, a capacitor will not carry current from a DC source.

If you connect that same capacitor to an AC source instead, then half the time the source is causing negative charge to build up on one plate, and the other half the time it is causing negative charge to build up on the other plate. Unlike what happened in the DC scenario, the reversal of the voltage source is the process that brings electrons back to the second plate, and on the other half cycle it brings electrons back to the first plate. The "steady state" condition is therefore a continuous flow of current through the capacitor. That current follows the same up/down/up/down pattern as the AC source. But it is reacting to the source, so the current does not reach its peak at the same time the voltage of the AC source reaches its peak.

 

[Volta]

Thanks Charlie, that was the best description I've ever heard on it!