AC Circuit Analysis & Power Flashcards

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

Answer: Be summed as phasor (vector) quantities

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

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

Answer: 159 Hz

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

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

Answer: IL = Iφ × √3

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

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

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

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

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

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

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

What is the average power delivered by a sinusoidal source to a purely reactive load?

Answer: Zero watts

A purely reactive load (ideal inductor or capacitor) stores and returns energy each cycle; net average power dissipated is zero.

A circuit draws 10 A at 120 V with a power factor of 0.8 lagging. What is the true power consumed?

Answer: 960 W

True power P = V × I × PF = 120 × 10 × 0.8 = 960 W.