4
1-27. Which, if any, of the following situations
is a major electrical difference between a
dc motor and a dc generator?
1. The armatures are different
2. The shunt connections are different
3. The dc generator requires a
commutator, the dc motor does not
4. None of the above
1-28. In a dc motor, what causes counter emf?
1. Improper commutation
2. Armature reaction
3. Generator action
4. Excessive speed
1-29. In a dc motor, how, if at all, does counter
emf affect speed?
1. It causes the speed to increase
2. It causes the speed to decrease
3. It causes rapid fluctuations of the
speed
4. It does not affect speed
1-30. What is the load on a dc motor?
1. The field current
2. The armature current
3. The mechanical device the motor
moves
4. The total current drawn from the
source
1-31. When a series dc motor is operated
without a load, which of the following
conditions occurs?
1. The armature draws excessive
current
2. The voltage requirement increases
3. The armature will not turn
4. The armature speeds out of control
1-32. A dc series motor is best suited for which
of the following applications?
1. Steady load, low torque
2. Variable load, low torque
3. Steady load, high torque
4. Variable load, high torque
1-33. What is the main advantage of a shunt
motor over a series motor?
1. A shunt motor develops higher
torque at lower speeds than a series
motor
2. A shunt motor can be operated at
higher speeds than a series motor
3. A shunt motor draws less current
from the source than a series motor
4. A shunt motor maintains a more
constant speed under varying load
conditions than a series motor
1-34. How can the direction of rotation be
changed in a dc motor?
1. Only by reversing the field
connections
2. Only by reversing the armature
connections
3. By reversing both the armature
connections and the field connections
4. 4.By reversing either the armature
connections or the field connections
1-35. When the voltage applied to the armature
of a dc shunt motor is decreased, what
happens to the motor speed?
1. It becomes uncontrollable
2. It decreases
3. It increases
4. The motor stops
1-36. In a dc motor, the neutral plane shifts in
what direction as the result of armature
reaction?
1. Clockwise
2. Counterclockwise
3. In the direction of rotation
4. Opposite the direction of rotation
