Journeyman Electrician’s Exam Transformers and Electrical Theory 2 — Questions and Answers
Question 1: What is the power factor of a purely resistive AC circuit?
- 0
- 0.5
- 0.707
- 1.0 (Correct answer)
Correct answer: 1.0
A purely resistive circuit has voltage and current in phase (0° phase angle), resulting in a power factor of 1.0 (unity).
Question 2: Apparent power in an AC circuit is expressed in which unit?
- Watts (W)
- Volt-amperes reactive (VAR)
- Volt-amperes (VA) (Correct answer)
- Kilowatts (kW)
Correct answer: Volt-amperes (VA)
Apparent power is the product of RMS voltage and RMS current expressed in volt-amperes (VA) or kilovolt-amperes (kVA).
Question 3: A circuit has 240V applied and draws 20 amperes. Using Ohm's Law, what is the circuit resistance?
- 4,800 ohms
- 12 ohms (Correct answer)
- 260 ohms
- 20 ohms
Correct answer: 12 ohms
R = V ÷ I = 240 ÷ 20 = 12 ohms.
Question 4: What is the correct formula for calculating true (real) power in a single-phase AC circuit?
- P = V × I
- P = V × I × PF (Correct answer)
- P = V × I × 1.732
- P = V × I × 2
Correct answer: P = V × I × PF
True power (watts) = Voltage × Current × Power Factor; omitting PF gives apparent power in VA, not real power.
Question 5: A series circuit has a resistance of 6 ohms and an inductive reactance of 8 ohms. What is the total impedance?
- 14 ohms
- 2 ohms
- 10 ohms (Correct answer)
- 48 ohms
Correct answer: 10 ohms
Z = √(R² + XL²) = √(6² + 8²) = √(36 + 64) = √100 = 10 ohms.
Question 6: What is the inductive reactance (XL) of a 0.2 Henry inductor at 60 Hz?
- 12 ohms
- 75.4 ohms (Correct answer)
- 37.7 ohms
- 120 ohms
Correct answer: 75.4 ohms
XL = 2πfL = 2 × 3.14159 × 60 × 0.2 = 75.4 ohms.
Journeyman Electrician’s Exam Transformers and Electrical Theory 2
What is the power factor of a purely resistive AC circuit?