I have this DC circuit:
Here, I am viewing the scope of the resistor (and as usual, green is voltage, and yellow is current). To my understanding, a capacitor is made by putting a layer of insulator between two metal plates. The plates store charges and the insulator prohibits the charges to pass through. But, here I can see that while the capacitor is charging, there is a voltage and a current passing across the resistor. If the capacitor had a layer of insulator in between the two metallic plates, then according to my understanding, it should not have allowed even a small amount of current to pass through because the insulative layer should have blocked the current. But as I can see, this is not the case.
So, my question is, how does a capacitor allow DC current to pass through while it is charging? I have tried to search a lot about it on the internet, but every site mentions that it does, not how it does.
Your help is much appreciated!
Best Answer
Is true that electrons don't go through the insulator of the capacitor, so there is no 'current flowing' in the sense of electrons passing from one side to the other.
But, as the charges in one plate of the cap have influence on the charges on the other side (attracting or pushing) there is some kind of 'current' going through. Maxwell called it 'displacement current'. And this 'current' goes through.
When charges start accumulating in one plate of the cap, they push the charges in the other side, at the beggining a lot, like a short circuit, until the cap is charged and it stops.
Actually what goes through is the energy that transport the electromagnetic field produced by the electrons moving. The energy is what goes through.
We tend to think in a electrical circuit like a pipe where electrons move around all the way inside the wire, making all the things in the circuit work. But this is not correct. The electrons don't need to move around like water in a closed pipe circuit. Electrons when moving produce a electromagnetic wave that is what move around and transport the energy.
In your example, electrons can never complete the circuit because the capacitor is in the middle.
With AC you can ligth a bulb, but electrons just move forward and backward all the time, as voltage sign changes. They 'vibrate' but in average they stay around the same place all the time. So they don't need to go to the bulb to bring the energy there. You can put a capacitor in series in the middle and the bulb will light anyway.