Capacitor Charging: How Current Flows Across a Capacitor

[likephysics]

How does current flow across a capacitor?
When a cap is charging up, the current is high initially and then gradually decreases as the charges start to build up on the plate of the capacitor.
I can't figure out how current flows from one plate to the other?
Its not like a resistor, where electrons flow thru the resistor.

 

[Born2bwire]

It doesn't, under ideal situations. If we are talking about a DC current, then the initial current during the transient is the result of building up the charges on opposite plates. There is no current going between the plates, but we are shifting around charges to the plates via the wires. Once we have enough charges built up such that we have the opposite potential across the plates that we are trying to apply, then the total voltage is zero and we cannot build up any more charges, making the current zero.

If we have an AC current, then we are just moving charges back and forth on and off the plates.

Current only flows between the plates (not via the wires) when we have dielectric breakdown. If the voltage across the plates gets high enough, the dielectric "breaks down" and allows a spark or current to run through the dielectric. This is rather undesirable since it circumvents the desired behavior of the capacitor and usually destroys the capacitor in the process. A simple example of dielectric breakdown is lightning (although I won't go as far as to say that the dielectric in capacitors turn to a plasma when they breakdown).

 

[astrokreng]

I can explain how current flows across a capacitor. A capacitor is an electrical component that stores electric charge. It consists of two conductive plates separated by an insulating material, known as a dielectric. When a voltage is applied across the capacitor, it starts to charge up.

The current flow in a capacitor is due to the movement of electrons from one plate to the other. Initially, when the capacitor is not charged, the plates have equal and opposite charges, and there is no net flow of electrons. However, when a voltage is applied, one plate becomes positively charged, while the other plate becomes negatively charged.

This creates an electric field between the plates, causing electrons to flow from the negatively charged plate to the positively charged plate. As electrons move from one plate to the other, the capacitor starts to charge up, and the current decreases. This is because the electric field between the plates increases, making it harder for electrons to move across the capacitor.

It is important to note that the movement of electrons across a capacitor is not the same as in a resistor. In a resistor, electrons flow through the material, while in a capacitor, they flow from one plate to the other through the insulating material. This is why the current flow in a capacitor is often referred to as displacement current.

In summary, the current flow across a capacitor is due to the movement of electrons from one plate to the other, driven by the electric field created by the voltage applied. As the capacitor charges up, the current decreases until it reaches a steady state, where there is no more movement of electrons across the capacitor. I hope this explanation helps to clarify the concept of current flow in a capacitor.