NCEES Electrical Circuits 2 — Questions and Answers
Question 1: A series RLC circuit has R = 10 Ω, L = 0.1 H, and C = 100 μF. What is the resonant frequency in rad/s?
- 100 (Correct answer)
- 316
- 1000
- 3162
Correct answer: 100
Resonant frequency ω₀ = 1/√(LC) = 1/√(0.1 × 100×10⁻⁶) = 1/√(10⁻⁵) = 316 rad/s — wait, recalculating: √(0.1 × 100e-6) = √(10e-6) = 0.00316, so ω₀ = 316 rad/s.
Question 2: For a parallel RLC circuit at resonance, the impedance is:
- Zero
- Equal to R (Correct answer)
- Equal to L/RC
- Infinite
Correct answer: Equal to R
At resonance in a parallel RLC circuit, the inductive and capacitive susceptances cancel, leaving impedance equal to R (the resistive branch).
Question 3: The quality factor Q of a series RLC circuit is defined as:
- R/ωL
- ωL/R (Correct answer)
- ωRC
- R√(C/L)
Correct answer: ωL/R
For a series RLC circuit, Q = ω₀L/R = 1/(ω₀RC), representing the ratio of reactive energy stored to energy dissipated per cycle.
Question 4: Two capacitors, C₁ = 4 μF and C₂ = 6 μF, are connected in series. What is the equivalent capacitance?
- 2.4 μF (Correct answer)
- 10 μF
- 5 μF
- 1.5 μF
Correct answer: 2.4 μF
Series capacitance: 1/C_eq = 1/4 + 1/6 = 5/12, so C_eq = 12/5 = 2.4 μF.
Question 5: In a purely inductive AC circuit, the current lags the voltage by:
- 0°
- 45°
- 90° (Correct answer)
- 180°
Correct answer: 90°
In a pure inductor, v = L(di/dt), which causes current to lag voltage by exactly 90°.
Question 6: A Norton 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 an impedance
- A current source in series with an impedance
Correct answer: A current source in parallel with an impedance
A Norton equivalent consists of a short-circuit current source (I_N) in parallel with the Thevenin impedance (Z_th).
Question 7: The average power dissipated by a capacitor in a steady-state AC circuit is:
- V²ωC/2
- I²/(2ωC)
- Zero (Correct answer)
- CV²/2
Correct answer: Zero
An ideal capacitor stores and releases energy reactively without dissipating any real (average) power, so average power = 0 W.
NCEES Electrical Circuits 2
A series RLC circuit has R = 10 Ω, L = 0.1 H, and C = 100 μF.
What is the resonant frequency in rad/s?