For high frequencies, capacitor acts as

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Examoogle · Accepted Answer

Short circuit

Explanation: At high frequencies, the capacitive reactance of a capacitor approaches zero, allowing it to behave as an ideal short circuit to alternating current. This occurs because the impedance offered by a capacitor is inversely proportional to the frequency of the applied signal.

Working Principle: The impedance of a capacitor is defined by the formula $X_C = \frac{1}{2\pi f C}$. As the frequency $f$ increases towards infinity, the denominator grows, causing $X_C$ to approach $0\,\Omega$. Consequently, the capacitor offers negligible opposition to the flow of high-frequency alternating current, acting as a short circuit.

Key Formulas: $X_C = \frac{1}{2\pi f C}$ — Capacitive reactance as a function of frequency; $Z = R + jX_C$ — General impedance of an RC circuit

Key Points: Capacitors act as open circuits to DC signals ($f=0$ Hz, $X_C 	o \infty$).; Capacitors act as short circuits to high-frequency AC signals ($f 	o \infty, X_C 	o 0$).; This property is widely used in coupling and bypass capacitors in electronic circuits.; The transition between open and short depends on the time constant $	au = RC$.

Advantages: Allows signal coupling in amplifiers while blocking DC bias.; Effective at filtering high-frequency noise when used in shunt.

Disadvantages: Idealized behavior; parasitic inductance at very high frequencies makes them behave as RLC circuits.; Real-world capacitors have Equivalent Series Resistance (ESR) that prevents a perfect short.

Applications: DC blocking capacitors in audio amplifiers.; High-frequency bypass capacitors in digital IC power supplies.; Coupling capacitors in RF circuits.

Additional Info: At low frequencies, the capacitor blocks current, acting as an open circuit.. The inverse relationship between frequency and reactance is a fundamental principle of frequency-dependent networks.

Answer: B is correct — At very high frequencies, the capacitive reactance approaches zero, making the capacitor behave as an ideal short circuit.

Exam Tip: Always remember the mnemonic 'CODC' (Capacitor Open for DC) to avoid confusion during rapid exam calculations.

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