BEE Fundamental Circuit Analysis 5 — Questions and Answers
Question 1: A delta (Δ) network has resistors R_AB = 30 Ω, R_BC = 30 Ω, R_CA = 30 Ω. What is the equivalent star (Y) resistance at each node?
- 30 Ω
- 10 Ω (Correct answer)
- 90 Ω
- 15 Ω
Correct answer: 10 Ω
For a balanced delta, R_Y = R_Δ / 3 = 30 / 3 = 10 Ω at each node.
Question 2: If the frequency of an AC source doubles, the inductive reactance X_L:
- Halves
- Stays the same
- Doubles (Correct answer)
- Quadruples
Correct answer: Doubles
X_L = 2πfL, so X_L is directly proportional to frequency — doubling f doubles X_L.
Question 3: In a circuit, a dependent voltage source whose value is controlled by a current elsewhere is called a:
- Current-controlled current source (CCCS)
- Voltage-controlled voltage source (VCVS)
- Current-controlled voltage source (CCVS) (Correct answer)
- Voltage-controlled current source (VCCS)
Correct answer: Current-controlled voltage source (CCVS)
A CCVS (transresistance source) produces a voltage proportional to a controlling current in another branch.
Question 4: What is the resonant frequency of a series RLC circuit with L = 10 mH and C = 40 µF?
- 251.6 Hz (Correct answer)
- 795.8 Hz
- 159.2 Hz
- 503.3 Hz
Correct answer: 251.6 Hz
f_0 = 1/(2π√LC) = 1/(2π√(0.01×40×10⁻⁶)) = 1/(2π×0.000632) ≈ 251.6 Hz.
Question 5: When applying the current divider rule, the current through branch R1 in a parallel circuit is:
- I_total × R1/(R1+R2)
- I_total × R2/(R1+R2) (Correct answer)
- I_total × (R1+R2)/R1
- I_total × R1×R2/(R1+R2)
Correct answer: I_total × R2/(R1+R2)
The current divider gives I_R1 = I_total × R2/(R1+R2) — the branch with lower resistance carries more current.
Question 6: An ideal voltage source has:
- Infinite internal resistance
- Zero internal resistance (Correct answer)
- Internal resistance equal to the load
- Resistance proportional to output current
Correct answer: Zero internal resistance
An ideal voltage source has zero internal resistance, maintaining constant terminal voltage regardless of load current.
Question 7: The power factor of a circuit carrying 10 A from a 120 V source while consuming 900 W of real power is:
- 0.90
- 0.75 (Correct answer)
- 1.0
- 0.60
Correct answer: 0.75
PF = P / (V × I) = 900 / (120 × 10) = 900 / 1200 = 0.75.
BEE Fundamental Circuit Analysis 5
A delta (Δ) network has resistors R_AB = 30 Ω, R_BC = 30 Ω, R_CA = 30 Ω.
What is the equivalent star (Y) resistance at each node?