LADWP Electric Distribution Mechanic
Trainee Exam – 3879 Exam Practice
Questions and Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
Electrical Fundamentals
1. Ohm's Law
A circuit has a resistance of 10 ohms and a current of 5 amperes. What is the
voltage?
A. 2 volts
B. 15 volts
C. 50 volts
D. 100 volts
Correct Answer: C. 50 volts
Rationale: Ohm's law states that voltage equals current multiplied by resistance.
Therefore, V = 5 A × 10 Ω = 50 V.
2. Electrical Current
Which unit is used to measure electrical current?
A. Volt
B. Ampere
C. Ohm
D. Watt
,Correct Answer: B. Ampere
Rationale: The ampere, commonly called an amp, is the SI unit used to measure
electric current. Voltage is measured in volts, resistance in ohms, and power in
watts.
3. Resistance
If resistance in a circuit increases while voltage remains constant, what happens
to current?
A. Current decreases
B. Current increases
C. Current remains exactly the same
D. Current becomes alternating current
Correct Answer: A. Current decreases
Rationale: According to Ohm's law, current equals voltage divided by resistance.
With constant voltage, increasing resistance results in lower current.
4. Electrical Power
An electrical load operates at 120 volts and draws 10 amperes. What is its power?
A. 12 watts
B. 120 watts
C. 1,200 watts
D. 12,000 watts
Correct Answer: C. 1,200 watts
Rationale: Electrical power can be calculated as P = V × I. Therefore, 120 volts × 10
amperes = 1,200 watts.
5. Conductors
,Which material is commonly used as an electrical conductor because of its
relatively high conductivity?
A. Rubber
B. Glass
C. Copper
D. Dry wood
Correct Answer: C. Copper
Rationale: Copper has high electrical conductivity and is widely used in electrical
conductors. Rubber, glass, and dry wood generally act as electrical insulators.
6. Insulation
What is the primary purpose of insulation around an electrical conductor?
A. Increase conductor resistance intentionally to zero current
B. Reduce unwanted current flow and help prevent contact with energized parts
C. Increase the conductor's operating voltage
D. Convert direct current to alternating current
Correct Answer: B. Reduce unwanted current flow and help prevent contact
with energized parts
Rationale: Electrical insulation separates conductors from other conductors,
grounded surfaces, and people. It helps control current paths and reduces the
likelihood of accidental contact.
7. Series Circuits
In a simple series circuit, what happens if one component becomes an open
circuit?
A. Current continues normally through every component
B. Voltage automatically doubles
C. The circuit path is interrupted
D. Resistance becomes zero
, Correct Answer: C. The circuit path is interrupted
Rationale: A series circuit has a single current path. An open at any point
interrupts that path and prevents normal current flow through the circuit.
8. Transformers
What is the primary function of a transformer in an electrical distribution system?
A. Change AC voltage from one level to another
B. Convert electrical energy directly into mechanical motion
C. Store compressed air
D. Measure conductor length
Correct Answer: A. Change AC voltage from one level to another
Rationale: Transformers use electromagnetic induction to change alternating
voltage levels. Distribution systems use transformers to provide appropriate
voltage levels for different portions of the system.
Mechanical Principles
9. Mechanical Advantage
A mechanical advantage of 4 means that an ideal machine can:
A. Produce four times the input force
B. Eliminate friction completely
C. Reduce the required input force to zero
D. Change electrical current into voltage
Correct Answer: A. Produce four times the input force
Rationale: Mechanical advantage describes the ratio of output force to input
force. An ideal mechanical advantage of 4 means the output force can be four
times the input force, although actual systems experience losses.
10. Levers
Trainee Exam – 3879 Exam Practice
Questions and Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
Electrical Fundamentals
1. Ohm's Law
A circuit has a resistance of 10 ohms and a current of 5 amperes. What is the
voltage?
A. 2 volts
B. 15 volts
C. 50 volts
D. 100 volts
Correct Answer: C. 50 volts
Rationale: Ohm's law states that voltage equals current multiplied by resistance.
Therefore, V = 5 A × 10 Ω = 50 V.
2. Electrical Current
Which unit is used to measure electrical current?
A. Volt
B. Ampere
C. Ohm
D. Watt
,Correct Answer: B. Ampere
Rationale: The ampere, commonly called an amp, is the SI unit used to measure
electric current. Voltage is measured in volts, resistance in ohms, and power in
watts.
3. Resistance
If resistance in a circuit increases while voltage remains constant, what happens
to current?
A. Current decreases
B. Current increases
C. Current remains exactly the same
D. Current becomes alternating current
Correct Answer: A. Current decreases
Rationale: According to Ohm's law, current equals voltage divided by resistance.
With constant voltage, increasing resistance results in lower current.
4. Electrical Power
An electrical load operates at 120 volts and draws 10 amperes. What is its power?
A. 12 watts
B. 120 watts
C. 1,200 watts
D. 12,000 watts
Correct Answer: C. 1,200 watts
Rationale: Electrical power can be calculated as P = V × I. Therefore, 120 volts × 10
amperes = 1,200 watts.
5. Conductors
,Which material is commonly used as an electrical conductor because of its
relatively high conductivity?
A. Rubber
B. Glass
C. Copper
D. Dry wood
Correct Answer: C. Copper
Rationale: Copper has high electrical conductivity and is widely used in electrical
conductors. Rubber, glass, and dry wood generally act as electrical insulators.
6. Insulation
What is the primary purpose of insulation around an electrical conductor?
A. Increase conductor resistance intentionally to zero current
B. Reduce unwanted current flow and help prevent contact with energized parts
C. Increase the conductor's operating voltage
D. Convert direct current to alternating current
Correct Answer: B. Reduce unwanted current flow and help prevent contact
with energized parts
Rationale: Electrical insulation separates conductors from other conductors,
grounded surfaces, and people. It helps control current paths and reduces the
likelihood of accidental contact.
7. Series Circuits
In a simple series circuit, what happens if one component becomes an open
circuit?
A. Current continues normally through every component
B. Voltage automatically doubles
C. The circuit path is interrupted
D. Resistance becomes zero
, Correct Answer: C. The circuit path is interrupted
Rationale: A series circuit has a single current path. An open at any point
interrupts that path and prevents normal current flow through the circuit.
8. Transformers
What is the primary function of a transformer in an electrical distribution system?
A. Change AC voltage from one level to another
B. Convert electrical energy directly into mechanical motion
C. Store compressed air
D. Measure conductor length
Correct Answer: A. Change AC voltage from one level to another
Rationale: Transformers use electromagnetic induction to change alternating
voltage levels. Distribution systems use transformers to provide appropriate
voltage levels for different portions of the system.
Mechanical Principles
9. Mechanical Advantage
A mechanical advantage of 4 means that an ideal machine can:
A. Produce four times the input force
B. Eliminate friction completely
C. Reduce the required input force to zero
D. Change electrical current into voltage
Correct Answer: A. Produce four times the input force
Rationale: Mechanical advantage describes the ratio of output force to input
force. An ideal mechanical advantage of 4 means the output force can be four
times the input force, although actual systems experience losses.
10. Levers
