BCIT ELECTRICAL DC MACHINES LEVEL 3
EXAM UPDATED ACTUAL 200+
QUESTIONS AND CORRECT ANSWERS
(2026/2027)
SECTION 1: DC MACHINE FUNDAMENTALS
Question 1
What is the main difference in the construction of a DC generator and a DC motor?
A) Direction of rotation
B) Type of field windings
C) Type of enclosure
D) They are constructed essentially the same
Answer: D) They are constructed essentially the same
Rationale: DC generators and DC motors are essentially the same machine in terms of
construction; the primary difference is their function . A DC motor converts electrical
power into mechanical power, while a DC generator converts mechanical power into
electrical power .
,Question 2
The rotating part of an electrical generator (or motor) is called the:
A) Rotor
B) Stator
C) Commutator
D) Field yoke
Answer: A) Rotor
Rationale: The rotor (or armature) is the rotating part of an electrical machine. The stator
is the stationary part that houses the field poles and provides the magnetic field .
Question 3
What is the electrical function of the commutator?
A) To increase voltage output
B) To reverse armature connections to maintain unidirectional current in the external
circuit
C) To convert AC to DC
D) To regulate field current
Answer: B) To reverse armature connections to maintain unidirectional current in
the external circuit
Rationale: The commutator's primary function is to reverse the connections to the
armature coils at the appropriate time to maintain unidirectional current in the external
circuit. It acts as a mechanical rectifier, converting the alternating current induced in the
armature windings into direct current .
Question 4
Which of the following is a common brush material used in DC machines?
,A) Carbon
B) Graphite
C) Metal-graphite
D) All of the above
Answer: D) All of the above
Rationale: Carbon, graphite, and metal-graphite are all common brush materials used in
DC machines . The choice depends on the specific application, voltage, and current
requirements.
Question 5
What is the function of field poles in a DC machine?
A) Support the armature
B) Produce the magnetic field required for operation
C) Transfer current to the armature
D) Reduce sparking at the brushes
Answer: B) Produce the magnetic field required for operation
Rationale: The field poles produce the magnetic field required for the operation of the DC
machine . The main pole pieces, made of soft iron or silicon steel, provide the magnetic
field when their windings are energized .
Question 6
DC machines commonly use which type of bearings?
A) Sleeve bearings
B) Ball bearings
C) Both sleeve and ball bearings
D) Needle bearings
Answer: C) Both sleeve and ball bearings
, Rationale: DC machines commonly use both sleeve and ball bearings in their end shields .
Grease nipples in the end shields indicate that the machine contains sleeve or ball
bearings that require periodic lubrication .
SECTION 2: ARMATURE WINDINGS
Question 7
What are the three basic types of armature windings?
A) Series, shunt, and compound
B) Lap, wave, and frog-leg
C) Closed, open, and semi-closed
D) Single-layer, double-layer, and random
Answer: B) Lap, wave, and frog-leg
Rationale: The three basic types of armature windings are lap-wound, wave-wound, and
frog-leg wound . Frog-leg winding is the most common type and offers a series-parallel
combination .
Question 8
Which armature winding is connected in parallel for high-current, low-voltage
applications?
A) Wave wound
B) Lap wound
C) Frog-leg wound
D) Series wound
Answer: B) Lap wound
EXAM UPDATED ACTUAL 200+
QUESTIONS AND CORRECT ANSWERS
(2026/2027)
SECTION 1: DC MACHINE FUNDAMENTALS
Question 1
What is the main difference in the construction of a DC generator and a DC motor?
A) Direction of rotation
B) Type of field windings
C) Type of enclosure
D) They are constructed essentially the same
Answer: D) They are constructed essentially the same
Rationale: DC generators and DC motors are essentially the same machine in terms of
construction; the primary difference is their function . A DC motor converts electrical
power into mechanical power, while a DC generator converts mechanical power into
electrical power .
,Question 2
The rotating part of an electrical generator (or motor) is called the:
A) Rotor
B) Stator
C) Commutator
D) Field yoke
Answer: A) Rotor
Rationale: The rotor (or armature) is the rotating part of an electrical machine. The stator
is the stationary part that houses the field poles and provides the magnetic field .
Question 3
What is the electrical function of the commutator?
A) To increase voltage output
B) To reverse armature connections to maintain unidirectional current in the external
circuit
C) To convert AC to DC
D) To regulate field current
Answer: B) To reverse armature connections to maintain unidirectional current in
the external circuit
Rationale: The commutator's primary function is to reverse the connections to the
armature coils at the appropriate time to maintain unidirectional current in the external
circuit. It acts as a mechanical rectifier, converting the alternating current induced in the
armature windings into direct current .
Question 4
Which of the following is a common brush material used in DC machines?
,A) Carbon
B) Graphite
C) Metal-graphite
D) All of the above
Answer: D) All of the above
Rationale: Carbon, graphite, and metal-graphite are all common brush materials used in
DC machines . The choice depends on the specific application, voltage, and current
requirements.
Question 5
What is the function of field poles in a DC machine?
A) Support the armature
B) Produce the magnetic field required for operation
C) Transfer current to the armature
D) Reduce sparking at the brushes
Answer: B) Produce the magnetic field required for operation
Rationale: The field poles produce the magnetic field required for the operation of the DC
machine . The main pole pieces, made of soft iron or silicon steel, provide the magnetic
field when their windings are energized .
Question 6
DC machines commonly use which type of bearings?
A) Sleeve bearings
B) Ball bearings
C) Both sleeve and ball bearings
D) Needle bearings
Answer: C) Both sleeve and ball bearings
, Rationale: DC machines commonly use both sleeve and ball bearings in their end shields .
Grease nipples in the end shields indicate that the machine contains sleeve or ball
bearings that require periodic lubrication .
SECTION 2: ARMATURE WINDINGS
Question 7
What are the three basic types of armature windings?
A) Series, shunt, and compound
B) Lap, wave, and frog-leg
C) Closed, open, and semi-closed
D) Single-layer, double-layer, and random
Answer: B) Lap, wave, and frog-leg
Rationale: The three basic types of armature windings are lap-wound, wave-wound, and
frog-leg wound . Frog-leg winding is the most common type and offers a series-parallel
combination .
Question 8
Which armature winding is connected in parallel for high-current, low-voltage
applications?
A) Wave wound
B) Lap wound
C) Frog-leg wound
D) Series wound
Answer: B) Lap wound
