1) Iron losses in a D.C. machine are independent of variations in______________? a. speed b. load c. voltage d. speed and voltage
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2) In D.C. generators, current to the external circuit from armature is given through_____________? a. commutator b. solid connection c. slip rings d. none of above
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3) Brushes of D.C. machines are made of_________? a. carbon b. soft copper c. hard copper d. all of above
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4) If a D.C. generator fails to build up the probable cause could not be_____________? a. imperfect brush contact b. field resistance less than the critical resistance c. no residual magnetism in the generator d. faulty shunt connections tending to reduce the residual magnetism
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5) 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
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6) 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
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7) The material for commutator brushes is generally_______________? a. mica b. copper c. cast iron d. carbon
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8) The insulating material used between the commutator segments is normally_____________? a. graphite b. paper c. mica d. insulating varnish
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9) 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 interpolar region d. are farthest from the poles
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10) 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 mag¬netisation c. crossmagnetisation as well as demagnetising d. cross magnetisation only
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11) Armature reaction of an unsaturated D.C. machine is_____________? a. crossmagnetising b. demagnetising c. magnetising d. none of above
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12) D.C. generators are connected to the busbars or disconnected from them only under the floating condition________________? a. to avoid sudden loading of the primemover b. to avoid mechanicaljerk to the shaft c. to avoid burning of switch contacts d. all above
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13) 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
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14) Equilizer rings are required in case armature is_______________? a. wave wound b. lap wound c. delta wound d. duplex wound
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15) Welding generator will have____________? a. lap winding b. wave winding c. delta winding d. duplex wave winding
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16) 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
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17) 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
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18) Flashing the field of D.C. generator means:______________? a. neutralising residual magnetism b. creating residual magnetism by a D.C. source c. making the magnetic losses of forces parallel d. increasing flux density by adding extra turns of windings on poles
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19) The function of pole shoes in the case of D.C. machine is______________? a. to reduce the reluctance of the mag¬netic 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
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20) In the case of lap winding resultant pitch is____________? a. multiplication of front and back pitches b. division of front pitch by back pitch c. sum of front and back pitches d. difference of front and back pitches
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