2
1-9. How can you vary the strength of the
magnetic field in a dc generator?
1. By varying the armature current
2. By varying the speed of armature
rotation
3. By varying the voltage applied to the
electromagnetic field coils
4. By varying the polarity of the field
poles
1-10. Under which of the following conditions
does sparking occur between the brushes
and the commutator?
1. When operating under normal
conditions
2. When there is improper commutation
3. When there is an excessive load
current
4. When commutation is in the neutral
plane
1-11. Distortion of the main field by
interaction with the armature field
defines what term?
1. Commutation
2. Mutual reaction
3. Armature reaction
4. Mutual induction
1-12. Distortion of the main field by
interaction with the armature field can be
compensated for by the use of
1. slip rings
2. interpoles
3. a commutator
4. special brushes
1-13. Motor reaction in a dc generator is a
physical force caused by the magnetic
interaction between the armature and the
field. What effect, if any, does this force
have on the operation of the generator?
1. It tends to oppose the rotation of the
armature
2. It tends to aid the rotation of the
armature
3. It causes the generator to vibrate
4. None
1-14. In dc generators, copper losses are
caused by which of the following
factors?
1. Reluctance in the field poles
2. Resistance in the armature winding
3. Reactance in the armature and field
windings
4. All of the above
1-15. Eddy currents in armature cores are kept
low by which of the following actions?
1. Using powdered iron as a core
material
2. Limiting armature current
3. Insulating the core
4. Laminating the iron in the core
1-16. What makes the drum-type armature
more efficient than the Gramme-ring
armature?
1. The drum-type armature has more
windings than the Gramme-ring
armature
2. The drum-type armature can be
rotated faster than the Gramme-ring
armature
3. The drum-type armature coils are
fully exposed to the magnetic field,
while the Gramme-ring armature
coils are only partially exposed to the
magnetic field
4. The drum-type armature has a
laminated core, while the Gramme-
ring armature has a solid core
