 ## electrical

### Synchronous Motor MCQ Objective Questions and Answers Page - 1

1.
 Synchronous motors generally have A Salient pole rotor B Smooth cylindrical rotor C Either salient pole or smooth cylindrical rotor D None of the above Answer : Select Correct Ans Explanation :
2.
 Number of slip rings in a 3-kphase synchronous motor will be A 0 B 1 C 2 D 3 or 4 Answer : Select Correct Ans Explanation :
3.
 An ideal synchronous motor has no starting torque because the A Rotor is made up of salient poles B Relative velocity between the stator and the rotor mmfs is zero C Relative  velocity between the  stator and rotor mmfs is not zero D Rotor winding is highly reactive Answer : Select Correct Ans Explanation :
4.
 In a synchronous motor A The rotor mmf and stator mmf are stationary with respect to each other B Rotor mmf rotates slightly faster in comparison to stator mmf C None f the above D Answer : Select Correct Ans Explanation :
5.
 A synchronous machine is revolving armature and stationary field type Under steady running conditios the air gap field A Rotates ate synchronous speed  with respect to stator B Rotates at synchronous speed in the direction of rotation of rotor C Remains stationary with respect to statorRemains stationary with respect to stator D Remains stationary with respect to rotor. Answer : Select Correct Ans Explanation :
6.
 In a synchronous machine, if the armature field axisis ahead of the field flux axis in the direction of rotation the machine operating is A Synchronous motor B Synchronous generator C Asynchronous motor D Asynchronous generator Answer : Select Correct Ans Explanation :
7.
 In a synchronous machine if the axis of the filed flux coincides with that of armature flux, the machine A Will operate smoothly without any vibration B Is said to be floating C Is operating as a synchronous generator D Is operating as a synchronous motor Answer : Select Correct Ans Explanation :
8.
 In  a 3-phase synchronous motor A Remains constant at all loads B Varies with load C Varies with speed D Varies with power factor Answer : Select Correct Ans Explanation :
9.
 In a 3-phase synchronous motor A The filed mmf leads the air gap flux leads the armature mmf B The armature mmf leads the air gpap flux and air gap flux leads the field mmf C The armature mmf leads the air gap flux and air gap flux lags behind the field mmf D None of the above Answer : Select Correct Ans Explanation :
10.
 What is the angle between the induced voltage and supply voltage of a  synchronous motor under running condition A Zero B Greater than zero but ≤ 900 C Between 900 and 1800 D >180 Answer : Select Correct Ans Explanation :
11.
 The  relative speed between  the magnetic fields of stator  and rotor under steady state operation is zero for A A dc machine B An induction machine C A synchronous machine D All the above machine Answer : Select Correct Ans Explanation :
12.
 A 3- phase synchronous motor has A High starting torque B No starting torque C Low starting  current D  Low starting torque Answer : Select Correct Ans Explanation :
13.
 A 10 pole , 25Hz alternator is directly coupled to and is driven by 60 Hz synchronous motor. What is the number of poles for the synchronous motor ? A 48 B 12 C 24 D 16 Answer : Select Correct Ans Explanation :
14.
 A 3- phase synchronous motor needs dc supply for excitation A Continuously B At the starting instant only C Of stator D None of these Answer : Select Correct Ans Explanation :
15.
 The  coupling magnetic field reaction with ___system(s) is essential for extracting energy from an electrical system A Mechanical B Electrical C Both electrical and mechanical D Answer : Select Correct Ans Explanation :
16.
 The armature current of a synchronous motor on no load A Leads the applied voltage by 900 B Lags behind the applied voltage by 900 C Is in phase will applied voltage D Zero Answer : Select Correct Ans Explanation :
17.
 As the load is increased on a synchronous motor, its  speed A Decreases B Increases C Remains constant and additional load is supplied by shift in relative position no of the rotor wi D Remains constant for some time and then falls abruptly Answer : Select Correct Ans Explanation :
18.
 The synchronous motor meets increase in load by taking more armature current as A The rotor pole falls back relative to the stator pole causing an increase in motor current B The back emf decreases causing an increase in motor current C Rotating field is strengthened causing an increase in motor current D None of the above Answer : Select Correct Ans Explanation :
19.
 A synchronous motor is operating with normal excitation . With the increase in load the armature current drawn from the supply main increases due to A Increase in back emf B Fall in motor speed C Increase in resultant voltage across the armature D Increase in power factor Answer : Select Correct Ans Explanation :
20.
 The resultant voltage acting across the armature circuit of a synchronous motor (Er) is the _____of induced emf in the armature circuit (Eb) and supply voltage V A Arithmetic sum B Arithmetic difference C Phasor difference D Phasor sum Answer : Select Correct Ans Explanation :
21.
 The magnitude of emf induced in the armature of a synchronous motor (Eb) depends upon A Supply voltage B Rotor excitation C Rotor speed D Flux density Answer : Select Correct Ans Explanation :