THE COMPREHENSIVE LADWP
ELECTRICAL MECHANIC–TEST
TECHNICIAN EXAM PREPARATION
GUIDE: PRACTICE QUESTIONS WITH
DETAILED RATIONALES AND
TECHNICAL EXPLANATIONS
Section 1: Electrical Theory and Ohm's Law (Questions 1-30)
Question 1
A 120V circuit draws 15A. What is the resistance?
A) 4Ω
B) 8Ω
C) 12Ω
D) 18Ω
Correct Answer: B) 8Ω
Rationale: According to Ohm's Law, R = V/I. Therefore, R = 120/15 = 8Ω .
Question 2
,In a purely inductive AC circuit, how does current relate to voltage?
A) Current leads voltage by 90°
B) Current lags voltage by 90°
C) Current is in phase with voltage
D) Current is 180° out of phase with voltage
Correct Answer: B) Current lags voltage by 90°
Rationale: In a purely inductive circuit, the voltage across the inductor
leads the current by 90° because the inductor opposes changes in current.
This means current lags voltage by 90° .
Question 3
Power factor is defined as:
A) kW / kVA
B) kVA / kW
C) kVAR / kW
D) kW × kVA
Correct Answer: A) kW / kVA
Rationale: Power factor is the ratio of true power (kW) to apparent power
(kVA). It represents the cosine of the phase angle between voltage and
current in an AC circuit .
Question 4
A three-phase 480V system supplies a 100A load with a power factor of 0.9.
What is the apparent power?
,A) 48 kVA
B) 74.8 kVA
C) 83.1 kVA
D) 90 kVA
Correct Answer: C) 83.1 kVA
Rationale: Apparent power in a three-phase system is calculated as S = √3
× V_L × I_L. S = 1.732 × 480 × 100 = 83,136 VA ≈ 83.1 kVA .
Question 5
What is the formula for three-phase power?
A) P = V × I
B) P = I² × R
C) P = √3 × V_L × I_L × PF
D) P = V² / R
Correct Answer: C) P = √3 × V_L × I_L × PF
Rationale: Three-phase power calculation requires the square root of 3
factor. The formula accounts for line voltage, line current, and power
factor .
Question 6
In a balanced 3-phase Wye system, what is the relationship between line
voltage and phase voltage?
A) V_L = V_ph
B) V_L = √3 × V_ph
, C) V_L = 2 × V_ph
D) V_L = V_ph / √3
Correct Answer: B) V_L = √3 × V_ph
Rationale: In a Wye configuration, the line-to-line voltage is √3 times the
phase-to-neutral voltage. For example, 120V phase gives 208V line-to-line .
Question 7
In a balanced 3-phase Wye system, what is the relationship between line
current and phase current?
A) I_L = √3 × I_ph
B) I_L = I_ph
C) I_L = I_ph / √3
D) I_L = 2 × I_ph
Correct Answer: B) I_L = I_ph
Rationale: In a Wye connection, the line current equals the phase current
because each line is directly connected to its respective phase winding .
Question 8
In a balanced 3-phase Delta system, what is the relationship between line
current and phase current?
A) I_L = I_ph
B) I_L = √3 × I_ph
C) I_L = I_ph / √3
D) I_L = 2 × I_ph
Correct Answer: B) I_L = √3 × I_ph
ELECTRICAL MECHANIC–TEST
TECHNICIAN EXAM PREPARATION
GUIDE: PRACTICE QUESTIONS WITH
DETAILED RATIONALES AND
TECHNICAL EXPLANATIONS
Section 1: Electrical Theory and Ohm's Law (Questions 1-30)
Question 1
A 120V circuit draws 15A. What is the resistance?
A) 4Ω
B) 8Ω
C) 12Ω
D) 18Ω
Correct Answer: B) 8Ω
Rationale: According to Ohm's Law, R = V/I. Therefore, R = 120/15 = 8Ω .
Question 2
,In a purely inductive AC circuit, how does current relate to voltage?
A) Current leads voltage by 90°
B) Current lags voltage by 90°
C) Current is in phase with voltage
D) Current is 180° out of phase with voltage
Correct Answer: B) Current lags voltage by 90°
Rationale: In a purely inductive circuit, the voltage across the inductor
leads the current by 90° because the inductor opposes changes in current.
This means current lags voltage by 90° .
Question 3
Power factor is defined as:
A) kW / kVA
B) kVA / kW
C) kVAR / kW
D) kW × kVA
Correct Answer: A) kW / kVA
Rationale: Power factor is the ratio of true power (kW) to apparent power
(kVA). It represents the cosine of the phase angle between voltage and
current in an AC circuit .
Question 4
A three-phase 480V system supplies a 100A load with a power factor of 0.9.
What is the apparent power?
,A) 48 kVA
B) 74.8 kVA
C) 83.1 kVA
D) 90 kVA
Correct Answer: C) 83.1 kVA
Rationale: Apparent power in a three-phase system is calculated as S = √3
× V_L × I_L. S = 1.732 × 480 × 100 = 83,136 VA ≈ 83.1 kVA .
Question 5
What is the formula for three-phase power?
A) P = V × I
B) P = I² × R
C) P = √3 × V_L × I_L × PF
D) P = V² / R
Correct Answer: C) P = √3 × V_L × I_L × PF
Rationale: Three-phase power calculation requires the square root of 3
factor. The formula accounts for line voltage, line current, and power
factor .
Question 6
In a balanced 3-phase Wye system, what is the relationship between line
voltage and phase voltage?
A) V_L = V_ph
B) V_L = √3 × V_ph
, C) V_L = 2 × V_ph
D) V_L = V_ph / √3
Correct Answer: B) V_L = √3 × V_ph
Rationale: In a Wye configuration, the line-to-line voltage is √3 times the
phase-to-neutral voltage. For example, 120V phase gives 208V line-to-line .
Question 7
In a balanced 3-phase Wye system, what is the relationship between line
current and phase current?
A) I_L = √3 × I_ph
B) I_L = I_ph
C) I_L = I_ph / √3
D) I_L = 2 × I_ph
Correct Answer: B) I_L = I_ph
Rationale: In a Wye connection, the line current equals the phase current
because each line is directly connected to its respective phase winding .
Question 8
In a balanced 3-phase Delta system, what is the relationship between line
current and phase current?
A) I_L = I_ph
B) I_L = √3 × I_ph
C) I_L = I_ph / √3
D) I_L = 2 × I_ph
Correct Answer: B) I_L = √3 × I_ph
