At DC, capacitor acts as _________.

Question

Examoogle · Accepted Answer

open circuit

Explanation: At DC steady-state, a capacitor acts as an open circuit because it reaches full charge and prevents any further flow of current. The capacitor blocks direct current while allowing only a momentary charging transient.

Working Principle: The capacitive reactance is defined as $X_C = \frac{1}{2\pi fC}$. In a DC circuit, the frequency $f$ is $0$ Hz. Substituting this into the formula gives $X_C = \frac{1}{2\pi(0)C} = \infty \Omega$. An infinite reactance represents an open circuit, which effectively prevents charge carriers from passing through the dielectric medium.

Key Formulas: $X_C = \frac{1}{2\pi f C}$ — Capacitive reactance formula; $I_C = C \frac{dv}{dt}$ — Current-voltage relationship for a capacitor

Key Points: Capacitors store energy in an electric field between their plates.; Once the capacitor voltage equals the source voltage, no current flows.; In AC circuits, capacitors exhibit frequency-dependent reactance.; A capacitor acts as a short circuit only during the instantaneous moment of charging when the potential difference is zero.

Advantages: Blocks DC component in signal processing (DC blocking); Used in coupling and decoupling circuit stages

Disadvantages: Cannot conduct steady-state DC current; Voltage across a capacitor cannot change instantaneously

Applications: Filter circuits (High-pass filters); Energy storage in power supplies; Signal coupling in amplifiers

Additional Info: In transient analysis, the capacitor behaves as a short circuit at $t = 0^+$ if initially uncharged.. Option B (short circuit) describes the behavior of an ideal inductor at DC.. Option C (resistor) is incorrect as capacitors are reactive elements, not dissipative.

Answer: A is correct — A capacitor behaves as an open circuit to DC because its reactance becomes infinite at zero frequency.

Exam Tip: Remember the mnemonic: 'Capacitor blocks DC, Inductor blocks AC (at high frequency).'

Related Questions

Discussion (0)