Question

How do capacitors behave in DC and AC circuit?

Answer 1

DC circuit with capacitors:

1. Capacitors are not used in DC circuits because a constant current cannot flow across one. When an uncharged capacitor C is placed at a voltage V across the terminals of the battery, a transient current is produced as the capacitor plates are charged. However, when the charge Q of the positive plate reaches the value of $Q=CV$, current flows.
2. Now there is no charge transfer because the electric field between the plates cancels out the effect of the battery's electric field. As the plates of a capacitor are charged in a DC circuit, it essentially acts as a circuit breaker.

AC circuit with capacitors:

1. Capacitors can be used as temporary storage devices after being connected to DC voltage. Once fully charged the capacitors will stop allowing any more electrons to reach the plates. Thus the capacitor stops the DC once it is fully charged.
2. When we add alternating voltage to it, the capacitor will charge and discharge at a frequency determined by the frequency of the supplied AC voltage. The frequency of the input signal, which is continuously charged, determines the capacitance of the capacitor in the AC circuit (or discharge).

Note: Capacitors are slowly charged in a DC circuit until the charging voltage of the capacitor equals the supply voltage. The capacitor will not allow any further charge to travel through it once it is fully charged. When capacitors are connected to an AC circuit, the voltage level of the circuit causes the charge to continuously charge and discharge. In AC circuits, capacitors are affected by the frequency of the supply voltage. In an AC capacitor circuit, the current always lags the voltage by $90$ degrees.