EETC Circuit Theory 4 — Questions and Answers
Question 1: Norton's equivalent circuit consists of:
- A voltage source in series with an impedance
- A current source in parallel with an impedance (Correct answer)
- A voltage source in parallel with a resistance
- A current source in series with a resistance
Correct answer: A current source in parallel with an impedance
Norton's equivalent circuit consists of an equivalent current source (IN) in parallel with an equivalent impedance (ZN).
Question 2: What is the phase angle of a series circuit with R = 30 Ω and XL = 40 Ω?
- 36.87°
- 53.13° (Correct answer)
- 45°
- 60°
Correct answer: 53.13°
θ = arctan(XL/R) = arctan(40/30) = arctan(1.333) ≈ 53.13°.
Question 3: In a parallel RLC circuit at resonance, the circuit impedance is:
- Zero
- Minimum
- Maximum (Correct answer)
- Equal to XL
Correct answer: Maximum
At resonance in a parallel RLC circuit, the impedance reaches its maximum value because the parallel LC combination presents infinite impedance.
Question 4: A 10 mH inductor carries a current that changes at 500 A/s. What is the induced EMF?
- 0.5 V
- 5 V (Correct answer)
- 50 V
- 50 mV
Correct answer: 5 V
e = L(di/dt) = 0.010 H × 500 A/s = 5 V.
Question 5: The maximum power transfer theorem states that maximum power is delivered to a load when the load impedance equals:
- Zero
- Twice the source impedance
- The complex conjugate of the source impedance (Correct answer)
- Half the source impedance
Correct answer: The complex conjugate of the source impedance
Maximum power transfer occurs when ZL = Zs* (complex conjugate), meaning equal resistance and opposite sign reactance.
Question 6: What is the total capacitance of three capacitors (4 µF, 6 µF, 12 µF) connected in series?
- 22 µF
- 2 µF (Correct answer)
- 4 µF
- 8 µF
Correct answer: 2 µF
1/C = 1/4 + 1/6 + 1/12 = 3/12 + 2/12 + 1/12 = 6/12, so C = 2 µF.
Question 7: In a balanced three-phase system, the line voltage is related to the phase voltage by a factor of:
- 1
- √2
- √3 (Correct answer)
- 2
Correct answer: √3
In a balanced three-phase wye-connected system, VLine = √3 × VPhase ≈ 1.732 × VPhase.
EETC Circuit Theory 4
Norton's equivalent circuit consists of: