Journeyman Electrician’s Exam Journeyman Electrician's Basic Formula 3 — Questions and Answers
Question 1: Two resistors of 12Ω and 6Ω are connected in parallel. What is the equivalent resistance?
- 18 Ω
- 9 Ω
- 4 Ω (Correct answer)
- 72 Ω
Correct answer: 4 Ω
1/R = 1/12 + 1/6 = 1/12 + 2/12 = 3/12; R = 4 Ω.
Question 2: A single-phase transformer has a primary voltage of 480V and a turns ratio of 4:1. What is the secondary voltage?
- 1,920 V
- 120 V (Correct answer)
- 240 V
- 480 V
Correct answer: 120 V
V_secondary = V_primary / turns ratio = 480 / 4 = 120 V.
Question 3: What formula is used to calculate electrical energy consumed over time?
- E = P / T
- E = P × T (Correct answer)
- E = V × T
- E = I × T
Correct answer: E = P × T
Energy (in watt-hours) = Power (watts) × Time (hours).
Question 4: A 10 kW load operates for 8 hours. How many kilowatt-hours (kWh) does it consume?
- 1.25 kWh
- 80 kWh (Correct answer)
- 18 kWh
- 0.8 kWh
Correct answer: 80 kWh
Energy = 10 kW × 8 h = 80 kWh.
Question 5: In a three-phase system, apparent power (VA) is calculated as:
- VA = V × I
- VA = √3 × V_L × I_L (Correct answer)
- VA = 3 × V × I × PF
- VA = V² / R
Correct answer: VA = √3 × V_L × I_L
Three-phase apparent power = √3 × line voltage × line current.
Question 6: A conductor has 0.5Ω of resistance and carries 10A. What is the power lost in the conductor?
- 5 W
- 50 W (Correct answer)
- 0.05 W
- 100 W
Correct answer: 50 W
P = I² × R = 10² × 0.5 = 100 × 0.5 = 50 W.
Question 7: What is the horsepower output of a motor drawing 746 W with 100% efficiency?
- 0.5 HP
- 1 HP (Correct answer)
- 2 HP
- 7.46 HP
Correct answer: 1 HP
1 HP = 746 W, so 746 W / 746 = 1 HP.
Journeyman Electrician’s Exam Journeyman Electrician's Basic Formula 3
Two resistors of 12Ω and 6Ω are connected in parallel.
What is the equivalent resistance?