15.  In case the field of a synchronous motor is underexcited, the power factor will be
A. leading
B. lagging
C. zero
D. unity

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16.  A synchronous running with normal excitation adjusts to increases in load essentially by increase in its
A. power factor
B. torque angle
C. back emf
D. armature current

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17. The back emf set up in the stator of a synchronous motor will depend on
A. rotor speed only
B. rotor excitation only
C. both rotor speed and totor excitation
D. coupling angle, rotor speed and excitation

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18. Which of the following is an unexcited single phase synchronous motor?
A. AC series motor
B. Universal motor
C. Reluctance motor
D. Repulsion motor

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19.  In a synchronous motor if the back emf generated in the armature at no load is approximately equal to the applied voltage, then
A. the torque generated is maximum
B. the excitation is said to be zero per cent
C. the excitation is said to be 100 per cent
D. the motor is said to be fully loaded

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20. In a synchronous motor, the torque angle is the
A. angle between the rotating stator flux and rotor poles
B. angle between meanetising current and back emf
C. angle between the supply voltage and the back emf
D. none of these

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21. Hunting in synchronous motor takes place when
A. friction in bearings is small
B. air gap is small
C. load is constant
D. load is variable

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