In a DC circuit, after a capacitor has charged, the capacitor behaves as which for the rest of the circuit?

• A. Short circuit
• B. Power source
• C. Open circuit
• D. Inductor

Answer: (C)

In DC circuits, once a capacitor has finished charging, it stops allowing current to flow and acts like an open circuit. This happens because the current through a capacitor is i = C dv/dt. After charging in a steady DC situation, the voltage across the capacitor is constant, so dv/dt = 0 and i = 0. With zero current through that branch, the path behaves as if there is a break in the circuit, i.e., an open circuit. The capacitor still stores energy in the electric field and holds a fixed voltage equal to the charging source, but it does not pass DC current. This is different from an inductor, which, in DC steady state, behaves like a short circuit.