BEE DC and AC Circuit Analysis 2 — Questions and Answers
Question 1: In a series RLC circuit at resonance, what happens to the impedance?
- Impedance equals resistance R (Correct answer)
- Impedance is maximum
- Impedance equals zero
- Impedance equals inductive reactance
Correct answer: Impedance equals resistance R
At resonance, inductive and capacitive reactances cancel, leaving only the resistance R as the total impedance.
Question 2: A delta-connected load has each branch impedance of 30 Ω. What is the equivalent wye impedance per phase?
- 10 Ω (Correct answer)
- 30 Ω
- 90 Ω
- 15 Ω
Correct answer: 10 Ω
For delta-to-wye conversion, Z_Y = Z_Δ / 3, so 30/3 = 10 Ω.
Question 3: What does the time constant τ represent in an RC circuit?
- Time for voltage to reach 63.2% of its final value (Correct answer)
- Time for voltage to reach 100% of its final value
- Time for voltage to reach 50% of its final value
- Time for the capacitor to fully discharge
Correct answer: Time for voltage to reach 63.2% of its final value
The time constant τ = RC is the time required for the capacitor voltage to rise to approximately 63.2% (1 - 1/e) of the source voltage.
Question 4: Using mesh analysis, what is the primary variable solved for?
- Mesh currents (Correct answer)
- Node voltages
- Branch resistances
- Power dissipation
Correct answer: Mesh currents
Mesh analysis assigns a loop current to each independent mesh and solves for those mesh currents using KVL equations.
Question 5: In a purely inductive AC circuit, what is the phase relationship between voltage and current?
- Voltage leads current by 90° (Correct answer)
- Current leads voltage by 90°
- Voltage and current are in phase
- Voltage leads current by 45°
Correct answer: Voltage leads current by 90°
In a pure inductor, the induced EMF (voltage) leads the current by 90° due to the inductor's opposition to current change.
Question 6: A circuit has a power factor of 0.8 lagging. What angle does this correspond to?
- 36.87° (Correct answer)
- 53.13°
- 45°
- 30°
Correct answer: 36.87°
Power factor = cos(θ), so θ = arccos(0.8) ≈ 36.87°, and lagging indicates an inductive circuit.
Question 7: Which theorem states that a linear two-terminal network can be replaced by a single voltage source in series with a single impedance?
- Thevenin's theorem (Correct answer)
- Norton's theorem
- Superposition theorem
- Maximum power transfer theorem
Correct answer: Thevenin's theorem
Thevenin's theorem replaces any linear network with an equivalent Vth in series with Zth as seen from the output terminals.
BEE DC and AC Circuit Analysis 2
In a series RLC circuit at resonance, what happens to the impedance?