DC Generator Construction and Operation
Exam Questions with Correct Answers
(VerifiedAnswers) Plus Rationales 2026 Q&A
Instant Download PDF
Practice Exam
1. What is the primary function of a DC generator?
A. To convert DC electrical energy into mechanical energy
B. To convert AC electrical energy into DC electrical energy
C. To convert mechanical energy into DC electrical energy
D. To store electrical energy for later use
Rationale: A DC generator converts mechanical energy supplied
to its shaft into electrical energy. The mechanical input causes
conductors to move through a magnetic field, inducing an
electromotive force (EMF). The commutator then mechanically
rectifies the internally generated alternating voltage so that the
external output is unidirectional DC.
2. Which principle is primarily responsible for the generation
of EMF in a DC generator?
,A. Ohm's law
B. Coulomb's law
C. Lenz's law alone
D. Faraday's law of electromagnetic induction
Rationale: Faraday's law states that an EMF is induced in a
conductor whenever the magnetic flux linking the conductor
changes. In a generator, armature conductors rotate through
the magnetic field, continuously changing the flux linkage and
producing an induced EMF.
3. Which rule determines the direction of the induced current
in a generator?
A. Fleming's left-hand rule
B. Right-hand screw rule
C. Fleming's right-hand rule
D. Kirchhoff's voltage rule
Rationale: Fleming's right-hand rule is used for generators. With
the thumb representing the direction of conductor motion, the
first finger representing magnetic-field direction, and the second
finger representing induced current, the rule establishes the
relationship among these three quantities.
,4. What is the main purpose of the commutator in a DC
generator?
A. To increase the magnetic flux
B. To reduce bearing friction
C. To regulate the prime mover speed
D. To mechanically rectify the internally generated voltage
Rationale: The EMF induced in an armature coil reverses
direction as the coil passes through successive magnetic poles.
The split commutator reverses the coil's external connections at
the appropriate time, producing a unidirectional voltage at the
brushes.
5. Which component carries current from the rotating
armature to the external circuit?
A. Field pole
B. Armature core
C. Brushes
D. Yoke
Rationale: Brushes are stationary electrical contacts that press
against the rotating commutator. They collect current from the
commutator segments and deliver it to the external circuit. In
many conventional machines, carbon or carbon-based brush
, materials are used because of their suitable electrical and
mechanical properties.
6. What is the stationary magnetic structure of a conventional
DC generator called?
A. Armature
B. Rotor
C. Stator
D. Commutator
Rationale: The stator is the stationary portion of the machine
and normally contains the magnetic poles and field windings.
The armature is the rotating portion in the conventional DC
generator arrangement.
7. What is the principal function of the yoke in a DC
generator?
A. To convert AC to DC
B. To support the brushes only
C. To provide mechanical support and a magnetic return path
D. To control the prime mover speed
Rationale: The yoke forms the outer frame of the generator. It
provides mechanical strength, supports the poles, and provides
a low-reluctance path for magnetic flux between the poles. In
Exam Questions with Correct Answers
(VerifiedAnswers) Plus Rationales 2026 Q&A
Instant Download PDF
Practice Exam
1. What is the primary function of a DC generator?
A. To convert DC electrical energy into mechanical energy
B. To convert AC electrical energy into DC electrical energy
C. To convert mechanical energy into DC electrical energy
D. To store electrical energy for later use
Rationale: A DC generator converts mechanical energy supplied
to its shaft into electrical energy. The mechanical input causes
conductors to move through a magnetic field, inducing an
electromotive force (EMF). The commutator then mechanically
rectifies the internally generated alternating voltage so that the
external output is unidirectional DC.
2. Which principle is primarily responsible for the generation
of EMF in a DC generator?
,A. Ohm's law
B. Coulomb's law
C. Lenz's law alone
D. Faraday's law of electromagnetic induction
Rationale: Faraday's law states that an EMF is induced in a
conductor whenever the magnetic flux linking the conductor
changes. In a generator, armature conductors rotate through
the magnetic field, continuously changing the flux linkage and
producing an induced EMF.
3. Which rule determines the direction of the induced current
in a generator?
A. Fleming's left-hand rule
B. Right-hand screw rule
C. Fleming's right-hand rule
D. Kirchhoff's voltage rule
Rationale: Fleming's right-hand rule is used for generators. With
the thumb representing the direction of conductor motion, the
first finger representing magnetic-field direction, and the second
finger representing induced current, the rule establishes the
relationship among these three quantities.
,4. What is the main purpose of the commutator in a DC
generator?
A. To increase the magnetic flux
B. To reduce bearing friction
C. To regulate the prime mover speed
D. To mechanically rectify the internally generated voltage
Rationale: The EMF induced in an armature coil reverses
direction as the coil passes through successive magnetic poles.
The split commutator reverses the coil's external connections at
the appropriate time, producing a unidirectional voltage at the
brushes.
5. Which component carries current from the rotating
armature to the external circuit?
A. Field pole
B. Armature core
C. Brushes
D. Yoke
Rationale: Brushes are stationary electrical contacts that press
against the rotating commutator. They collect current from the
commutator segments and deliver it to the external circuit. In
many conventional machines, carbon or carbon-based brush
, materials are used because of their suitable electrical and
mechanical properties.
6. What is the stationary magnetic structure of a conventional
DC generator called?
A. Armature
B. Rotor
C. Stator
D. Commutator
Rationale: The stator is the stationary portion of the machine
and normally contains the magnetic poles and field windings.
The armature is the rotating portion in the conventional DC
generator arrangement.
7. What is the principal function of the yoke in a DC
generator?
A. To convert AC to DC
B. To support the brushes only
C. To provide mechanical support and a magnetic return path
D. To control the prime mover speed
Rationale: The yoke forms the outer frame of the generator. It
provides mechanical strength, supports the poles, and provides
a low-reluctance path for magnetic flux between the poles. In
