CEP Electrical Theory & Principles 5 — Questions and Answers
Question 1: Which of the following correctly describes the behavior of an ideal voltage source?
- Its terminal voltage varies with load current
- It maintains constant terminal voltage regardless of load current (Correct answer)
- It maintains constant current regardless of load voltage
- Its output depends on the connected resistance
Correct answer: It maintains constant terminal voltage regardless of load current
An ideal voltage source has zero internal resistance and maintains its rated voltage regardless of the current drawn by the load.
Question 2: The phase angle (θ) of a series RL circuit with R = 30 Ω and XL = 40 Ω is:
- 36.87°
- 53.13° (Correct answer)
- 45°
- 90°
Correct answer: 53.13°
θ = arctan(XL/R) = arctan(40/30) = arctan(1.333) ≈ 53.13°, indicating current lags voltage by 53.13°.
Question 3: Eddy currents in transformer cores are minimized by:
- Using solid iron cores
- Increasing the operating frequency
- Laminating the core with thin insulated sheets (Correct answer)
- Reducing the number of turns
Correct answer: Laminating the core with thin insulated sheets
Laminated cores break the eddy current paths into smaller, higher-resistance loops, reducing eddy current losses proportional to lamination thickness squared.
Question 4: The Q factor (quality factor) of a series resonant circuit is defined as:
- Q = R / XL
- Q = XL / R (Correct answer)
- Q = R × XL
- Q = 1 / (R × XL)
Correct answer: Q = XL / R
The Q factor = XL/R (or XC/R) at resonance, representing the ratio of energy stored to energy dissipated per cycle.
Question 5: In the maximum power transfer theorem, maximum power is delivered to the load when:
- Load resistance is zero
- Load resistance equals twice the source resistance
- Load resistance equals the source resistance (Correct answer)
- Load resistance is infinite
Correct answer: Load resistance equals the source resistance
Maximum power transfer occurs when R_load = R_source (or Z_load = Z_source* for AC circuits), delivering 50% of source power to the load.
Question 6: What is the reactance of a 10 mH inductor at 60 Hz?
- 3.77 Ω (Correct answer)
- 37.7 Ω
- 0.377 Ω
- 377 Ω
Correct answer: 3.77 Ω
XL = 2πfL = 2π × 60 × 0.010 = 3.77 Ω; inductive reactance is directly proportional to frequency and inductance.
Question 7: Which of the following describes the behavior of a capacitor in a DC steady-state circuit?
- It acts as a short circuit
- It acts as an open circuit (Correct answer)
- It acts as a resistor with value 1/C
- It continuously charges and discharges
Correct answer: It acts as an open circuit
In DC steady state, no current flows through a fully charged capacitor, making it equivalent to an open circuit.
CEP Electrical Theory & Principles 5
Which of the following correctly describes the behavior of an ideal voltage source?