Licensed Electrical Contractor Electrical Contractor Electrical Theory & Fundamentals 1 — Questions and Answers
Question 1: A 480-volt circuit draws 16 amperes of current. What is the resistance of the load?
- 24 ohms
- 30 ohms (Correct answer)
- 496 ohms
- 7,680 ohms
Correct answer: 30 ohms
Using Ohm's Law, R = V ÷ I = 480 ÷ 16 = 30 ohms. Dividing the voltage by the current gives the resistance of the load.
Question 2: Three resistors of 10 ohms, 15 ohms, and 25 ohms are connected in series to a 150-volt source. What is the current flowing through the circuit?
- 1.5 amperes
- 2.0 amperes
- 3.0 amperes (Correct answer)
- 5.0 amperes
Correct answer: 3.0 amperes
In a series circuit, total resistance is the sum of all resistors: 10 + 15 + 25 = 50 ohms. Applying Ohm's Law: I = V ÷ R = 150 ÷ 50 = 3.0 amperes.
Question 3: An electric motor draws 12 amperes from a 240-volt supply. What is the power consumed by the motor?
- 252 watts
- 1,440 watts
- 2,880 watts (Correct answer)
- 28,800 watts
Correct answer: 2,880 watts
Power is calculated using P = V × I = 240 × 12 = 2,880 watts. This formula relates voltage, current, and power in a purely resistive or rated-load scenario.
Question 4: What is a defining characteristic of voltage in a parallel circuit?
- Voltage divides equally among all branches
- Voltage is highest across the branch with the most resistance
- Voltage across each branch equals the source voltage (Correct answer)
- Voltage decreases with each additional branch added
Correct answer: Voltage across each branch equals the source voltage
In a parallel circuit, all branches are connected directly across the same two nodes, so every branch sees the full source voltage regardless of its resistance.
Question 5: Two 40-microfarad capacitors are connected in series. What is the total capacitance of the combination?
- 10 µF
- 20 µF (Correct answer)
- 40 µF
- 80 µF
Correct answer: 20 µF
For capacitors in series, 1/C_total = 1/C1 + 1/C2 = 1/40 + 1/40 = 2/40, so C_total = 20 µF. Series capacitance behaves opposite to series resistance — it decreases.
Question 6: What is the standard frequency of alternating current (AC) supplied to residential and commercial buildings in the United States?
- 25 Hz
- 50 Hz
- 60 Hz (Correct answer)
- 120 Hz
Correct answer: 60 Hz
The U.S. power grid operates at 60 Hz, meaning the current completes 60 full cycles per second. Most other countries use 50 Hz as their standard frequency.
Licensed Electrical Contractor Electrical Contractor Electrical Theory & Fundamentals 1
A 480-volt circuit draws 16 amperes of current.
What is the resistance of the load?