LADWP ELECTRICAL CRAFT HELPER
TRANSFORMERS FUNDAMENTALS EXAM
WITH ACTUAL QUESTIONS AND VERIFIED
ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1. A single-phase transformer has a primary winding with 2,400 turns
and a secondary winding with 240 turns. If 2,400 V is applied to
the primary, what is the ideal secondary voltage?
A. 24 V
B. 120 V
C. 240 V
D. 2,400 V
Answer: C. 240 V
Rationale: The ideal transformer voltage relationship is V₁/V₂ = N₁/N₂.
Here, 2,400/240 = 10, so the secondary voltage is 2,400/10 = 240 V.
Because the secondary has one-tenth as many turns as the primary,
this is a step-down transformer.
2. What fundamental principle allows a conventional transformer to
transfer electrical energy from one circuit to another without a
direct electrical connection between the windings?
A. Electrostatic attraction
B. Mutual electromagnetic induction
1
,C. Mechanical coupling
D. Thermal conduction
Answer: B. Mutual electromagnetic induction
Rationale: A transformer operates through electromagnetic induction.
Alternating current in the primary winding establishes a changing
magnetic flux in the core, and that changing flux induces an
electromotive force in the secondary winding. The windings are
electrically isolated in a conventional transformer but magnetically
coupled through the core.
3. Why must the primary winding of an ordinary transformer
normally be supplied with alternating current rather than steady
direct current?
A. AC has lower resistance than DC
B. DC cannot produce any magnetic field
C. A changing magnetic flux is required to induce secondary voltage
D. Transformers can only operate at frequencies above 1,000 Hz
Answer: C. A changing magnetic flux is required to induce
secondary voltage
Rationale: Faraday's law requires changing magnetic flux to induce
voltage. AC continuously changes the current and therefore the
magnetic flux in the transformer core. With steady DC, there is only a
brief transient when power is initially applied; after that, the flux
becomes essentially constant and the transformer cannot sustain
normal secondary voltage.
4. A transformer has a primary voltage of 7,200 V and a secondary
voltage of 480 V. What type of transformer is this?
2
,A. Step-up transformer
B. Isolation transformer with a 1:1 ratio
C. Step-down transformer
D. Current transformer only
Answer: C. Step-down transformer
Rationale: The secondary voltage is substantially lower than the
primary voltage. A transformer that reduces voltage from a higher
primary value to a lower secondary value is classified as a step-down
transformer. A 7,200-to-480 V transformer has a voltage ratio of 15:1.
5. Which statement best describes the relationship between voltage
and current in an ideal transformer?
A. Both voltage and current always increase together
B. If voltage is stepped down, current capacity can increase
proportionally
C. Voltage changes but power always becomes zero
D. Current is completely independent of voltage
Answer: B. If voltage is stepped down, current capacity can increase
proportionally
Rationale: For an ideal transformer, input power approximately
equals output power. Therefore, when voltage is reduced, the available
current increases correspondingly, subject to the transformer's power
rating and losses. This is why transformers can transfer substantial
power at high voltage with comparatively lower current on the
transmission side.
6. A transformer has a primary winding of 1,000 turns and a
secondary winding of 500 turns. If the primary voltage is 4,800 V,
what ideal voltage should appear across the secondary?
3
, A. 960 V
B. 1,200 V
C. 2,400 V
D. 9,600 V
Answer: C. 2,400 V
Rationale: Using V₁/V₂ = N₁/N₂, the secondary voltage is 4,800 ×
(500/1,000) = 2,400 V. The secondary has half the number of turns, so
the ideal secondary voltage is half the primary voltage.
7. What is the primary purpose of the laminated iron or steel core in a
conventional power transformer?
A. To provide mechanical rotation
B. To provide a low-reluctance path for magnetic flux
C. To increase winding resistance
D. To eliminate the need for insulation
Answer: B. To provide a low-reluctance path for magnetic flux
Rationale: The magnetic core provides an efficient path for the
alternating magnetic flux linking the primary and secondary windings.
Laminations are used to reduce circulating eddy currents within the
core, thereby reducing energy losses and unwanted heating.
8. Why are transformer cores commonly constructed from thin
insulated laminations rather than one solid block of steel?
A. To increase eddy-current losses
B. To eliminate hysteresis completely
C. To reduce circulating eddy currents
D. To increase the winding turns ratio
Answer: C. To reduce circulating eddy currents
4
TRANSFORMERS FUNDAMENTALS EXAM
WITH ACTUAL QUESTIONS AND VERIFIED
ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1. A single-phase transformer has a primary winding with 2,400 turns
and a secondary winding with 240 turns. If 2,400 V is applied to
the primary, what is the ideal secondary voltage?
A. 24 V
B. 120 V
C. 240 V
D. 2,400 V
Answer: C. 240 V
Rationale: The ideal transformer voltage relationship is V₁/V₂ = N₁/N₂.
Here, 2,400/240 = 10, so the secondary voltage is 2,400/10 = 240 V.
Because the secondary has one-tenth as many turns as the primary,
this is a step-down transformer.
2. What fundamental principle allows a conventional transformer to
transfer electrical energy from one circuit to another without a
direct electrical connection between the windings?
A. Electrostatic attraction
B. Mutual electromagnetic induction
1
,C. Mechanical coupling
D. Thermal conduction
Answer: B. Mutual electromagnetic induction
Rationale: A transformer operates through electromagnetic induction.
Alternating current in the primary winding establishes a changing
magnetic flux in the core, and that changing flux induces an
electromotive force in the secondary winding. The windings are
electrically isolated in a conventional transformer but magnetically
coupled through the core.
3. Why must the primary winding of an ordinary transformer
normally be supplied with alternating current rather than steady
direct current?
A. AC has lower resistance than DC
B. DC cannot produce any magnetic field
C. A changing magnetic flux is required to induce secondary voltage
D. Transformers can only operate at frequencies above 1,000 Hz
Answer: C. A changing magnetic flux is required to induce
secondary voltage
Rationale: Faraday's law requires changing magnetic flux to induce
voltage. AC continuously changes the current and therefore the
magnetic flux in the transformer core. With steady DC, there is only a
brief transient when power is initially applied; after that, the flux
becomes essentially constant and the transformer cannot sustain
normal secondary voltage.
4. A transformer has a primary voltage of 7,200 V and a secondary
voltage of 480 V. What type of transformer is this?
2
,A. Step-up transformer
B. Isolation transformer with a 1:1 ratio
C. Step-down transformer
D. Current transformer only
Answer: C. Step-down transformer
Rationale: The secondary voltage is substantially lower than the
primary voltage. A transformer that reduces voltage from a higher
primary value to a lower secondary value is classified as a step-down
transformer. A 7,200-to-480 V transformer has a voltage ratio of 15:1.
5. Which statement best describes the relationship between voltage
and current in an ideal transformer?
A. Both voltage and current always increase together
B. If voltage is stepped down, current capacity can increase
proportionally
C. Voltage changes but power always becomes zero
D. Current is completely independent of voltage
Answer: B. If voltage is stepped down, current capacity can increase
proportionally
Rationale: For an ideal transformer, input power approximately
equals output power. Therefore, when voltage is reduced, the available
current increases correspondingly, subject to the transformer's power
rating and losses. This is why transformers can transfer substantial
power at high voltage with comparatively lower current on the
transmission side.
6. A transformer has a primary winding of 1,000 turns and a
secondary winding of 500 turns. If the primary voltage is 4,800 V,
what ideal voltage should appear across the secondary?
3
, A. 960 V
B. 1,200 V
C. 2,400 V
D. 9,600 V
Answer: C. 2,400 V
Rationale: Using V₁/V₂ = N₁/N₂, the secondary voltage is 4,800 ×
(500/1,000) = 2,400 V. The secondary has half the number of turns, so
the ideal secondary voltage is half the primary voltage.
7. What is the primary purpose of the laminated iron or steel core in a
conventional power transformer?
A. To provide mechanical rotation
B. To provide a low-reluctance path for magnetic flux
C. To increase winding resistance
D. To eliminate the need for insulation
Answer: B. To provide a low-reluctance path for magnetic flux
Rationale: The magnetic core provides an efficient path for the
alternating magnetic flux linking the primary and secondary windings.
Laminations are used to reduce circulating eddy currents within the
core, thereby reducing energy losses and unwanted heating.
8. Why are transformer cores commonly constructed from thin
insulated laminations rather than one solid block of steel?
A. To increase eddy-current losses
B. To eliminate hysteresis completely
C. To reduce circulating eddy currents
D. To increase the winding turns ratio
Answer: C. To reduce circulating eddy currents
4
