DC MACHINES 6

51. Which of the following motors is used for rolling mills ?
a) D.C. shunt motor
b) D.C. cumulative compound motor.
c) D.C. series motor.
d) D.C. differential compound motor.
ans. b

52. Armature reaction is attributed to
a) the effect of magnetic field setup by armature current.
b) the effect of magnetic field setup by field current.
c) copper loss in the armature.
d) the effect of magnetic field setup by back emf.
ans. a

53. What will happen if the supply terminals of dc shunt motor are interchanged?
a) Motor will stop.
b) Motor will run at its normal speed in the same direction as it was running .
c) The direction of rotation will reverse.
d) Motor will run at a speed lower than the normal speed in the same direction.
ans. b

54. When the electric train is moving down a hill the dc motor acts as
a) dc series motor
b) dc shunt motor
c) dc series generator
d) dc shunt generator
ans.c

55. Which of the following dc motors is suitable for high starting torque?
a) shunt motor
b) cumulative compound motor
c) series motor
d) compound motor.
ans. c

56. For which of the following dc motors is the typical field of application mentioned?
a) shunt motor - electric trains
b) series motor - machine tools
c) series motor - belt drive
d) compound motor - fly wheel drive
ans. d

57. The generator of a power station produces an electric pressure by
a) conversion point
b) magnetic induction
c) conversion of light
d) mechanical pressure
ans. d

58. Why is the air gap between stator and armature of an electric motor kept as small as possible?
a) To get stronger magnetic field
b) To make the rotation easier.
c) To reach a higher speed of rotation.
d) To improve the air circulation.
ans. a

59. Which of the following types of generators gives constant voltage output at all loads?
a) series generator
b) shunt generator
c) short shunt compound generator
d) level compound generator
ans. d

60. Interpoles are meant for
a) increasing the speed of the motor
b) decreasing counter emf
c) reducing sparking at the commutator.
d) converting armature current to dc.
ans. c