31. Brushes of D.C. machines are made of
(A) carbon
(B) soft copper
(C) hard copper
(D) all of above
Ans: A
32. If B is the flux density, I the length of conductor and v
the velocity of conductor, then induced e.m.f. is given by
(A)
Blv
(B)
Blv2
(C)
Bl2v
(D)
Bl2v2
Ans: A
33. In case of a 4-pole D.C. generator provided with a two
layer lap winding with sixteen coils, the pole pitch will be
(A) 4
(B) 8
(C) 16
(D) 32
Ans: B
34. The material for commutator brushes is generally
(A) mica
(B) copper
(C) cast iron
(D) carbon
Ans: D
35. The insulating material used between the commutator
segments is normally
(A) graphite
(B) paper
(C) mica
(D) insulating varnish
Ans: C
36. In D.C. generators, the brushes on commutator remain in
contact with conductors which
(A) lie under south pole
(B) lie under north pole
(C) lie under inter-polar region
(D) are farthest from the poles
Ans: C
37. If brushes of a D.C. generator are moved in order to
bring these brushes in magnetic neutral axis, there will be
(A) demagnetisation only
(B) cross magnetisation as well as
magnetisation
(C) cross-magnetisation as well as
demagnetising
(D) cross magnetisation only
Ans: C
38. Armature reaction of an unsaturated D.C. machine is
(A) cross-magnetising
(B) demagnetising
(C) magnetising
(D) none of above
Ans: A
39. D.C. generators are connected to the bus-bars or
disconnected from them only under the floating condition
(A) to avoid sudden loading of the prime mover
(B) to avoid mechanical jerk to the shaft
(C) to avoid burning of switch contacts
(D) all above
Ans: D
40. Eddy currents are induced in the pole shoes of a D.C.
machine due to
(A) oscillating magnetic field
(B) pulsating magnetic flux
(C) relative rotation between field and
armature
(D) all above
Ans: C
41. Equalizer rings are required in case armature is
(A) wave wound
(B) lap wound
(C) delta wound
(D) duplex wound
Ans: B
42. Welding generator will have
(A) lap winding
(B) wave winding
(C) delta winding
(D) duplex wave winding
Ans: A
43. In case of D.C. machine winding, number of commutator
segments is equal to
(A) number of armature coils
(B) number of armature coil sides
(C) number of armature conductors
(D) number of armature turns
Ans: A
44. For a D.C. machines laboratory following type of D.C.
supply will be suitable
(A) rotary converter
(B) mercury are rectifier
(C) induction motor D.C. generator set
(D) synchronous motor D.C. generator set
Ans: C
45. The function of pole shoes in the case of D.C. machine is
(A) to reduce the reluctance of the
magnetic path
(B) to spread out the flux to achieve
uniform flux density
(C) to support the field coil
(D) to discharge all the above functions
