What is true of a capacitor in a DC circuit?

• A. The capacitor will discharge until voltage is removed then act as an open.
• B. Capacitors cannot be used in DC circuits.
• C. The capacitor will charge to the source voltage and then act as a short in the circuit.
• D. The capacitor will charge to the source voltage and then act as an open in the circuit.

Answer: (D)

In DC circuits, a capacitor starts by letting current flow as it charges, so it initially behaves like a short. As charging continues, the current tapers off and the voltage across the capacitor rises toward the source voltage. When the capacitor voltage has reached the source voltage, there is no steady DC current through the capacitor, so it effectively becomes an open circuit. That’s why a capacitor in a DC circuit charges to the source voltage and then acts as an open in the circuit.

The other ideas don’t fit: it doesn’t remain a short after charging, and in a DC circuit it doesn’t automatically discharge to zero unless there’s a path to discharge or the source is removed. Capacitors can indeed be used in DC circuits for various reasons, such as decoupling and DC blocking.