What happens when a capacitor is fully charged?

• A. It enhances the current flow in a circuit
• B. It blocks DC while allowing AC to pass
• C. It maintains a constant voltage
• D. It short-circuits the power source

Answer: (B)

When a capacitor is fully charged, it effectively reaches a state where it cannot store any more charge. This condition allows it to exhibit specific behaviors in electrical circuits. One crucial aspect is its ability to block direct current (DC) while allowing alternating current (AC) to pass through.

This is due to the fundamental properties of capacitors. With DC, once the capacitor is charged, it creates a voltage across its plates equal to the voltage of the power source. The current flow ceases because there is no change in voltage; hence, the capacitor acts as an open circuit to DC. Conversely, for AC, which continuously changes direction and magnitude, the capacitor can charge and discharge in response to the varying voltage. This alternating action allows AC to pass through the capacitor effectively.

Understanding this behavior is vital in various applications, such as filtering in power supplies and coupling/decoupling signals in circuits. The ability of capacitors to block DC while passing AC is a fundamental characteristic that exploits their phase-shifting capabilities in AC circuits.