In our previous posts, we discussed about the basic theory and working of capacitor. In this post, we will understand about “ Capacitor charging and discharging cycle ”.

Capacitor charging and discharging cycle provides a better understanding of a capacitor function. Lets take an example of a capacitor circuit in which there is no resistor/resistance. When a capacitor is not having any charge, that time there will not be any potential (voltage) across its plates. Accordingly, when the capacitor is in full charged mode, it will break the circuit as the potential of the power source (DC) and the capacitor will be same. This means that there will not be any current flowing in the circuit.

However, this condition can never be achieved as in any case there will be some internal resistance in the circuit. We all know that internal resistance of a circuit can never be zero ideally. It is therefore, we can say that a capacitor is always connected to a power source through a resistance/resistor and there is always a minimal current flowing in the circuit even when the capacitor is fully charged.

Capacitor charging and discharging circuit

Capacitor circuit

When the capacitor is provided a dc voltage, it charges at a quite higher rate initially. But as the time passes, this rate of charging slowly decreases. Keep it in mind that a capacitor can never be fully charged to its maximum capacity as the capacitor has an asymptotic charging curve. Yet, we can say that beyond a certain level, it may be considered fully charged.

Capacitor charging and dischargingHowever, in case of alternating power source, the capacitor will be in frequent mode of charging and discharging cycle. The rate of rise or fall in the potential of capacitor depends on the value of resistance implying on the circuit.

Now tell me something. Why capacitor allow Alternating current(AC) to flow, but blocks the Direct Current (DC)? We have already discussed it.


Try to think logically and you can answer it. Still No????

Here is your answer. As in case of alternating voltage, the capacitor frequently charges and discharges. Thus, there will always exist a continuous flow of alternating current. However, in case of Direct voltage, As the capacitor is charged to its maximum capacity, the potential of the DC source and the capacitor is almost same. And so, the capacitor will not allow further charge to pass through it. Accordingly, there will not be any flow of direct current across the capacitor.