Correct Answer

Concept & PrincipleElectricalBasic Electrical

Option D

$Z$

Quick Summary: In an A.C. circuit, impedance is defined as the total opposition offered to the flow of alternating current by a combination of resistance, inductive reactance, and capacitive reactance. It is represented by the symbol $Z$ and is measured in Ohms ($\Omega$).

💡 Explanation

In an A.C. circuit, impedance is defined as the total opposition offered to the flow of alternating current by a combination of resistance, inductive reactance, and capacitive reactance. It is represented by the symbol $Z$ and is measured in Ohms ( $\Omega$ ).

🔢 Key Formulas

$Z = \sqrt{R^2 + X^2}$ — Basic impedance magnitude formula

$Z = V_{rms} / I_{rms}$ — Impedance as the ratio of effective voltage to current

⚙️ Working Principle

Impedance represents the complex sum of the real part (Resistance $R$ ) and the imaginary part (Net Reactance $X = X_L - X_C$ ). It dictates the phase shift between voltage and current in an A.C. circuit, acting as the complex equivalent of D.C. resistance in Ohm's Law ( $V = I \cdot Z$ ).

📌 Key Points

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Impedance ( $Z$ ) accounts for both magnitude and phase shift in A.C. circuits.
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The SI unit of impedance is the Ohm ( $\Omega$ ).
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In a purely resistive circuit, $Z = R$ .
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In a purely reactive circuit, $Z = |X_L - X_C|$ .

✅ Advantages

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Allows for unified analysis of passive A.C. networks.
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Enables the use of complex numbers for circuit calculation.

❌ Disadvantages / Limitations

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Frequency dependent behavior complicates calculations.
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Vector analysis required instead of simple scalar algebra.

🛠️ Applications / Uses

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Power system analysis and load flow studies.
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Impedance matching in RF communication and signal transmission.

📄 Additional Information

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Resistance ( $R$ ) is the real part; Inductive Reactance ( $X_L$ ) and Capacitive Reactance ( $X_C$ ) form the imaginary part.
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Option A is Resistance, Option B is Inductive Reactance, Option C is Capacitive Reactance; none represent the total complex impedance.

📊 Diagram / Illustration

✅

D is correct — Impedance represents the total opposition to alternating current, symbolized by the letter Z.

Core Concepts Used

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Phasor Algebra Complex Impedance A.C. Circuit Theory

💡 EXAM TIP

Remember that impedance is a complex quantity ( $Z = R + jX$ ); when calculating the magnitude, use the Pythagorean theorem as $Z = \sqrt{R^2 + X^2}$ .

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