CET AC Circuit Analysis & Power 3 — Questions and Answers
Question 1: The skin effect in AC conductors causes current to concentrate at the:
- Center of the conductor
- Outer surface of the conductor (Correct answer)
- Midpoint between center and surface
- Negative half of the conductor
Correct answer: Outer surface of the conductor
The skin effect forces AC current toward the outer surface of a conductor, increasing effective resistance at higher frequencies.
Question 2: In a parallel RLC circuit, what condition defines resonance?
- Total admittance is maximum
- Susceptances cancel and total current is minimum (Correct answer)
- Current through R equals current through L
- Impedance equals zero
Correct answer: Susceptances cancel and total current is minimum
At parallel resonance, inductive and capacitive susceptances cancel, minimizing total current and maximizing impedance.
Question 3: What is the RMS value of a sine wave with a peak voltage of 170 V?
- 85 V
- 120.2 V (Correct answer)
- 240 V
- 170 V
Correct answer: 120.2 V
VRMS = Vpeak / √2 = 170 / 1.414 ≈ 120.2 V.
Question 4: Power factor correction in industrial facilities is most commonly achieved by adding:
- Resistors in parallel with the load
- Capacitor banks in parallel with inductive loads (Correct answer)
- Inductors in series with capacitive loads
- Transformers across the supply
Correct answer: Capacitor banks in parallel with inductive loads
Capacitor banks supply leading reactive power that cancels the lagging reactive power of inductive loads, improving power factor.
Question 5: In an AC circuit, complex power S is expressed as:
- S = V × I
- S = P + jQ (Correct answer)
- S = P − jQ
- S = P / Q
Correct answer: S = P + jQ
Complex power S = P + jQ, where P is real (true) power in watts and Q is reactive power in VAR.
Question 6: What is the bandwidth of a series resonant circuit with f0 = 10 kHz and Q = 50?
- 500 Hz
- 200 Hz (Correct answer)
- 5 kHz
- 50 kHz
Correct answer: 200 Hz
BW = f0 / Q = 10,000 / 50 = 200 Hz.
Question 7: Which waveform has an RMS value equal to its average value?
- Sine wave
- Triangle wave
- Square wave (Correct answer)
- Sawtooth wave
Correct answer: Square wave
A perfect square wave alternates between two equal and opposite values, so its RMS and average (of the absolute value) are both equal to the peak value.
CET AC Circuit Analysis & Power 3
The skin effect in AC conductors causes current to concentrate at the: