Correct Answer

Concept & PrincipleElectricalBasic Electrical

Option C

$X_C$

Quick Summary: Capacitive reactance is the opposition offered by a capacitor to the flow of alternating current. It is denoted by the symbol $X_C$ and is measured in ohms ($\Omega$).

💡 Explanation

Capacitive reactance is the opposition offered by a capacitor to the flow of alternating current. It is denoted by the symbol $X_C$ and is measured in ohms ( $\Omega$ ).

🔢 Key Formulas

$X_C = \frac{1}{2\pi f C}$ — Capacitive reactance formula where $f$ is frequency and $C$ is capacitance.

$I = \frac{V}{X_C}$ — Relation between voltage and current in a purely capacitive circuit.

⚙️ Working Principle

When an AC voltage is applied to a capacitor, it constantly charges and discharges. The alternating electric field causes a displacement current, and because the capacitor stores energy in an electric field, it provides an opposition to current flow that is inversely proportional to both the frequency of the AC signal and the capacitance value.

📌 Key Points

▸
Capacitive reactance is inversely proportional to frequency ( $X_C \propto \frac{1}{f}$ ).
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In a DC circuit ( $f=0$ ), $X_C$ becomes infinite, acting as an open circuit.
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The unit of $X_C$ is ohms ( $\Omega$ ).
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Current leads voltage by $90°$ in a purely capacitive circuit.

✅ Advantages

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Used in AC coupling to block DC components.
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Essential for filter circuits and oscillators.

❌ Disadvantages / Limitations

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Provides high impedance at very low frequencies.
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Susceptible to dielectric losses at high voltages.

🛠️ Applications / Uses

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Signal filtering in audio electronics.
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Power factor correction in industrial systems.

📄 Additional Information

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Option A (R) denotes Resistance, which is frequency-independent.
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Option B ( $X_L$ ) denotes Inductive Reactance, where $X_L = 2\pi f L$ .
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Option D (Z) denotes Impedance, the total opposition to current in an RLC circuit.

📊 Diagram / Illustration

✅

C is correct — $X_C$ is the standard notation for capacitive reactance representing the opposition to current in a capacitor.

Core Concepts Used

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AC Circuit Theory Capacitor Physics Frequency Response

💡 EXAM TIP

Remember that $X_C$ decreases as frequency increases, whereas $X_L$ increases with frequency; this inverse relationship is a frequent topic in competitive AC circuit problems.

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