50. In three-phase induction motors sometimes copper bars are placed deep in the rotor to
A. improve starting torque
B. reduce copper losses
C. improve efficiency
D. improve power factor

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51.  In a three-phase induction motor
A. power factor at starting is high as compared to that while running
B. power factor at starting is low as compared to that while running
C. power factor at starting in the same as that while running
D. power factor remains through out constant

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52.  The value of transformation ratio of an induction motor can be found by
A. open-circuit test only
B. short-circuit test only
C. stator resistance test
D. none of the above

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53.  The power scale of circle diagram of an induction motor can be found from
A. stator resistance test
B. no-load test only
C. short-circuit test only
D. none of the above

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54. The shape of the torque/slip curve of induction motor is
A. parabola
B. hyperabola
C. rectangular parabola
D. straight line

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55. A change of 4% of supply voltage to an induction motor will produce a change of approximately
A. 4% in the rotor torque
B. 8% in the rotor torque
C. 12% in the rotor torque
D. 16% in the rotor torque

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56. The stating torque of the slip ring induction motor can be increased by adding
A. external inductance to the rotor
B. external resistance to the rotor
C. external capacitance to the rotor
D. both resistance and inductance to rotor

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