DC Motors Exam Questions with Correct
Answers (VerifiedAnswers) Plus Rationales
2026 Q&A Instant Download PDF
DC Motors Practice Exam
Question 1
What is the primary principle of operation of a DC motor?
A. Electromagnetic induction only
B. Interaction between a magnetic field and a current-carrying
conductor
C. Electrostatic attraction between charged plates
D. Chemical conversion of electrical energy into heat
Rationale: A DC motor operates because a current-carrying
conductor placed in a magnetic field experiences a mechanical
force. The direction of this force depends on both the direction
of current and the magnetic field. This electromagnetic force
produces torque on the motor's armature, causing it to rotate.
Electromagnetic induction is important in motor back EMF, but
the fundamental motor action is the force produced by the
interaction of current and magnetic flux.
,Question 2
What type of energy conversion takes place in a DC motor?
A. Mechanical energy into electrical energy
B. Thermal energy into electrical energy
C. Electrical energy into mechanical energy
D. Chemical energy into mechanical energy
Rationale: A DC motor receives electrical power at its terminals
and converts most of that input power into mechanical output
power. Some of the input energy is inevitably lost through
winding resistance, brush contact, magnetic losses, friction,
windage, and other mechanisms. A generator performs the
reverse principal conversion, changing mechanical energy into
electrical energy.
Question 3
Which component of a conventional DC motor carries current
through the rotating armature conductors?
A. Yoke
B. Pole shoe
C. Commutator
D. Bearing
Rationale: The commutator is a segmented copper assembly
connected to the armature windings. Through the brushes, it
,supplies current to the rotating armature and reverses the
current direction in individual armature coils at appropriate
points during rotation. This switching action allows the
developed torque to remain substantially unidirectional.
Question 4
What is the main function of the brushes in a DC motor?
A. Increase the magnetic flux
B. Support the motor shaft
C. Provide electrical contact between the stationary circuit and
rotating commutator
D. Reduce armature resistance
Rationale: Brushes provide a sliding electrical connection
between the stationary external circuit and the rotating
commutator. They are commonly made from carbon or carbon-
based materials because they provide suitable electrical
conductivity while limiting mechanical wear. Brush condition,
pressure, alignment, and contact surface can significantly
influence commutation and motor performance.
Question 5
Which DC motor has the field winding connected in parallel
with the armature?
, A. Series motor
B. Compound motor only
C. Shunt motor
D. Universal motor
Rationale: In a DC shunt motor, the field winding is connected in
parallel, or shunt, with the armature circuit. Consequently, the
field winding receives approximately the supply voltage.
Because the shunt field is relatively independent of armature
current, the motor normally provides good speed regulation
compared with a series motor.
Question 6
Which DC motor generally produces the highest starting
torque?
A. Shunt motor
B. Separately excited motor
C. Series motor
D. Permanent-magnet motor
Rationale: In a series motor, the field winding is connected in
series with the armature, so the same current flows through
both. At starting, the current can be large, producing strong
field flux and large armature torque. Since torque is
Answers (VerifiedAnswers) Plus Rationales
2026 Q&A Instant Download PDF
DC Motors Practice Exam
Question 1
What is the primary principle of operation of a DC motor?
A. Electromagnetic induction only
B. Interaction between a magnetic field and a current-carrying
conductor
C. Electrostatic attraction between charged plates
D. Chemical conversion of electrical energy into heat
Rationale: A DC motor operates because a current-carrying
conductor placed in a magnetic field experiences a mechanical
force. The direction of this force depends on both the direction
of current and the magnetic field. This electromagnetic force
produces torque on the motor's armature, causing it to rotate.
Electromagnetic induction is important in motor back EMF, but
the fundamental motor action is the force produced by the
interaction of current and magnetic flux.
,Question 2
What type of energy conversion takes place in a DC motor?
A. Mechanical energy into electrical energy
B. Thermal energy into electrical energy
C. Electrical energy into mechanical energy
D. Chemical energy into mechanical energy
Rationale: A DC motor receives electrical power at its terminals
and converts most of that input power into mechanical output
power. Some of the input energy is inevitably lost through
winding resistance, brush contact, magnetic losses, friction,
windage, and other mechanisms. A generator performs the
reverse principal conversion, changing mechanical energy into
electrical energy.
Question 3
Which component of a conventional DC motor carries current
through the rotating armature conductors?
A. Yoke
B. Pole shoe
C. Commutator
D. Bearing
Rationale: The commutator is a segmented copper assembly
connected to the armature windings. Through the brushes, it
,supplies current to the rotating armature and reverses the
current direction in individual armature coils at appropriate
points during rotation. This switching action allows the
developed torque to remain substantially unidirectional.
Question 4
What is the main function of the brushes in a DC motor?
A. Increase the magnetic flux
B. Support the motor shaft
C. Provide electrical contact between the stationary circuit and
rotating commutator
D. Reduce armature resistance
Rationale: Brushes provide a sliding electrical connection
between the stationary external circuit and the rotating
commutator. They are commonly made from carbon or carbon-
based materials because they provide suitable electrical
conductivity while limiting mechanical wear. Brush condition,
pressure, alignment, and contact surface can significantly
influence commutation and motor performance.
Question 5
Which DC motor has the field winding connected in parallel
with the armature?
, A. Series motor
B. Compound motor only
C. Shunt motor
D. Universal motor
Rationale: In a DC shunt motor, the field winding is connected in
parallel, or shunt, with the armature circuit. Consequently, the
field winding receives approximately the supply voltage.
Because the shunt field is relatively independent of armature
current, the motor normally provides good speed regulation
compared with a series motor.
Question 6
Which DC motor generally produces the highest starting
torque?
A. Shunt motor
B. Separately excited motor
C. Series motor
D. Permanent-magnet motor
Rationale: In a series motor, the field winding is connected in
series with the armature, so the same current flows through
both. At starting, the current can be large, producing strong
field flux and large armature torque. Since torque is
