Working of Capacitor

Capacitor which is passive devices block DC current and allows AC current passes but how does it Block DC current and how does it manage to allow AC current to pass?

Capacitor is nothing but two conducting plates with an insulator between them so when we apply DC, the insulator block the current flow from one terminal to another terminal that means it acts as a open circuit.

In AC,

capacitor has a tendency to oppose the change in voltage across the plates so when we apply ac, it draws some current and cause conduction means short circuit.

The capacitor content is directly proportional to the change in voltage.

Capacitor has reactance given by

Xc=1/wc

and we know w=2 times 3.41 times frequency so reactance is inversely proportional to frequency.

For D.C freq is zero.

So Xc will be infinite i.e open circuit similarly for A.C it will be short circuit.

The Capacitor plates are separated by Dielectric. When a positive charge is induced on one plate a negative charge will be induced on another plate by the electrostatic induction. Now consider the capacitor has 2 plates 1) Plate A and 2) Plate B.

Let Plate A is facing the Ac source and Plate B be facing the other side. Consider The AC source first creates the +ve potential so a positive charges get accumulated in the Plate A. By Induction a negative Charge get accumulated in the other plate and when the AC source polarity changes the potential at Plate A changes and so does the potential of Plate B. Thus as the potential at Plate varies sinusoidal and potential at plate B also Varies Sinusoidal now this Plate B acts as the source for other side of the circuit and thus a similar sinusoidal wave of same frequency is generated from the Plate B.