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SymbolsTransformerRelayPower-SystemBasic-electricalACSR-ConductorCircuit-BreakerInterview-questions-of-Basic-ElectricityInterview-questions-of-transformerInsulatorCurrent-TransformerMCQMCQ-powersystemThermal-power-stationInterview-questions-of-Power-SystemPower-ElectronicsInterview-questions-of-Underground-CableInterview-questions-of-IlluminationIlluminationMCQ-of-ElectronicsMCQ-of-Basic-ElectricalMCQ-of-Transformers MCQ-of-D.C-motor MCQ-of-D.C-generatorsMCQ-Control-SystemMCQ-Measurementsmcq-of-Generation-power-systemMCQ-of-Induction-MotorMCQ-of-Transmission-Distribution

Multiple Choice Question (MCQ) of D.C. Machines page-4

31. The back emf of a dc motor depends on

a) Field flux
b) Shape of conductors
c) Type of slip rings
d) Brush material

Ans: (a)

32. The back emf of dc motor depends on

a) Armature speed N
b) Field flux ɸ
c) Number of armature conductors
d) All of these

Ans: (d)

33. The air gap between the stator and armature of a dc motor is kept small in order to

a) Facilitate high speed operation without vibration
b) Produce strong magnetic field
c) Reduce noise
d) Improve cooling

Ans: (b)

34. In a dc machine prominent and noisy blue and green sparks indicate

a) Excessive brush wear
b) Winding fault
c) Worn out insulation
d) None of these

Ans: (b)

35. When the direction of power flow reverses, a differentially compounded motor becomes

a) Differentially compounded generator
b) A shunt generator
c) Cumulatively compounded generator
d) A series generator

Ans: (c)

36. When the direction of power flow reverses, a cumulatively compounded motor becomes

a) A differentially compounded generator
b) A cumulative compounded generator
c) A shunt generator
d) A series generator

Ans: (a)

37. Frog leg winding is

a) Same as simplex winding
b) Same as duplex winding
c) Combined lap and wave windings on a single rotor
d) Duplex wave winding on a single rotor

Ans: (c)

38. In a compound dc motor, the shunt field winding as compared to series winding will have

a) More turns of smaller diameter
b) Less turns of larger diameter
c) More turns of larger diameter
d) Less turns of smaller diameter

Ans: (a)

39. The flux is maximum in following unit of a dc motor

a) Yoke leading end of pole shoe
b) Trailing end of pole shoe
c) Yoke
d) Any of the above

Ans: (c)

40. In dc motor, the amount of flux leakage depends on

a) Length of air gap
b) Shape of the magnet core
c) Flux density used in core and teeth
d) All of these

Ans: (d)

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