11. The function of pole shoes in a dc machine is to
- support the field coils
- reduce the reluctance of the magnetic path
- spread out the lux to achieve uniform flux distribution in the air gap
- all of the above
12. Poles of dc machine are often laminated to
- reduce the pulsation loss
- reduce armature reaction
- reduce iron weight
- dissipate more heat
13. The ventilating ducts in most of the dc machines are
- radial
- longitudinal
- radial as well as longitudinal
- none of these
14. Armature of a dc machine is made of
- conducting material
- insulating material
- non-ferrous material
- silicon steel
15. Which of the following parts are subjected to iron loss?
- yoke
- armature core
- brushes
- pole core
16. The armature of a dc machine is laminated to reduce
- hysteresis loss
- eddy current loss
- the mass
- the inductance
17. What are the slot wedges in a dc machine made of?
- mild steel
- silicon steel
- fibre
- cast iron
18. The teeth in the armature of a dc machine are sometimes skewed. This is done to reduce
- hysteresis loss
- copper loss
- eddy current loss
- vibrations
19. The commutator of a dc motor serves the purpose of
- changing ac to dc
- converting dc into ac
- reducing friction
- avoiding arc at the brushes
20. The factors responsible for rapid wear of brushes are
- high mica insulation between commutator bars
- excessive spring pressure
- abrasion from dust
- all of the above
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