CET AC Circuit Analysis & Power 5

Question 1

Using Kirchhoff's Voltage Law (KVL) in an AC circuit, phasor voltages must:

Accepted Answer

Be summed as phasor (vector) quantities

Answer

In AC circuits, KVL requires phasor (vector) addition of voltages because magnitude alone ignores phase differences.

Question 2

What is the resonant frequency of a series LC circuit with L = 10 mH and C = 100 µF?

Accepted Answer

159 Hz

Answer

f0 = 1/(2π√LC) = 1/(2π√(0.01 × 0.0001)) = 1/(2π × 0.001) ≈ 159 Hz.

Question 3

In a delta (Δ) connected three-phase load, the relationship between line current (IL) and phase current (Iφ) is:

Accepted Answer

IL = Iφ × √3

Answer

In a delta connection, line current = phase current × √3 because each line current is the phasor sum of two phase currents.

Question 4

What does Thevenin's theorem allow you to do when analyzing AC circuits?

Accepted Answer

Replace a complex network with an equivalent voltage source and series impedance

Answer

Thevenin's theorem replaces any linear two-terminal AC network with an equivalent voltage source (Vth) in series with an equivalent impedance (Zth).

Question 5

In superposition analysis of AC circuits containing multiple sources of different frequencies, why must each frequency be analyzed separately?

Accepted Answer

Different frequencies produce different phase angles, so impedances differ at each frequency

Answer

Capacitive and inductive reactances depend on frequency, so impedance values change for each source frequency, requiring separate analysis.

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