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Single Phase Induction Motor MCQ Question & Answer

1.A single-phase induction motor is

  • ASelf-starting
  • BNot self-starting
  • CSelf-starting with the help of an auxiliary winding
  • DNone of the above
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Answer:

Self-starting with the help of an auxiliary winding

Explanation:

2.A single-phase induction motor is running at N rpm. Its synchronous speed is Ns. If its slip with respect to forward field is s, what is the slip with respect to the backward field?

  • As
  • B– s
  • C(1 – s)
  • D(2 – s)
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Answer:

(2 – s)

Explanation:

3.A rotating magnetic field is produced by current is two windings displaced by 90 electrical degrees. This is the principle of

  • APhase sequence
  • BPhase splitting
  • CPhase timing
  • DNone of these
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Answer:

Phase splitting

Explanation:

4.The torque developed by a single-phase induction motor drop to zero at

  • ASynchronous speed
  • BA speed slightly above synchronous speed
  • CA speed slightly below synchronous speed
  • DNone of the above 
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Answer:

A speed slightly below synchronous speed

Explanation:

5.The no load current of a single-phase induction motor is around ____% of full load current

  • A10
  • B20
  • C40
  • D80
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Answer:

40

Explanation:

6.The power factor at which single phase induction motors usually operate is

  • A0.7 lag
  • B0.8 lag
  • C0.7 lead
  • DUnity
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Answer:

0.7 lag

Explanation:

7.Which of the following tests are performed on single phase ac motors?

  • AStator winding resistance test
  • BBlocked rotor test
  • CNo load test
  • DAll of the above 
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Answer:

All of the above 

Explanation:

8.Single phase induction motors are made self-starting by 

  • AIncreasing rotor resistance
  • BUsing an external starting device
  • CProviding an additional winding on the stator called the auxiliary winding
  • DAny of the above methods
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Answer:

Providing an additional winding on the stator called the auxiliary winding

Explanation:

9.The two windings provided on the stator of a single-phase induction motor, one main winding and the other auxiliary winding are connected

  • AIn parallel
  • BIn series
  • CEither in series or in parallel depending on the design of the motor
  • DThrough inductive coupling
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Answer:

In parallel

Explanation:

10.The stator winding of a single-phase induction motor is splatted into two parts in order to 

  • AImprove efficiency
  • BImprove power factor 
  • CDevelop starting torque 
  • DIncrease speed
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Answer:

Develop starting torque 

Explanation:

11.In a single-phase induction motor

  • ABoth the main and auxiliary windings are placed on stator
  • BBoth the main and auxiliary windings are placed on rotor 
  • CMain winding is placed on stator and auxiliary winding on rotor
  • DAuxiliary winding is placed on stator and main winding on rotor
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Answer:

Both the main and auxiliary windings are placed on stator

Explanation:

12.Phase splitting can be accomplished in a single-phase induction motor.

  • AOnly by adding capacitor in series with the auxiliary winding
  • BOnly by causing the auxiliary winding to have high reactance 
  • COnly by causing the auxiliary winding to have low resistance
  • DBy any one of the above three methods
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Answer:

By any one of the above three methods

Explanation:

13.In a split phase motor, the ratio of number of turns of auxiliary winding to that on main winding is

  • AUnity
  • BLess than one
  • CMore than one
  • DTwo
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Answer:

Less than one

Explanation:

14.Why is a centrifugal switch used in a single-phase induction motor? 

  • ATo protect the motor from overloading
  • BTo improve the starting performance of the motor
  • CTo cut off the starting winding at an appropriate instant
  • DTo cut in the capacitor during running conditions. 
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Answer:

To cut off the starting winding at an appropriate instant

Explanation:

15.Centrifugal switch fitted on the rotor will operate when 

  • ARotor speed reaches its rated conditions 
  • BRotor speed exceeds 70 per cent of its rated value
  • CRotor speed exceeds synchronous speed
  • DRotor speed exceeds 40 per cent of its rated value 
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Answer:

Rotor speed exceeds 70 per cent of its rated value

Explanation:

16.The torque speed characteristic of two-phase induction motor is largely affected by 

  • AVoltage
  • BSpeed
  • CX/R ratio
  • DSupply frequency
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Answer:

X/R ratio

Explanation:

17.The direction of rotation of a split phase induction motor can be reversed by reversing the connections to the supply of 

  • AAuxiliary winding only
  • BMain winding only
  • CWither (a) and (b)
  • DBoth (a) and (b) simultaneously 
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Answer:

Wither (a) and (b)

Explanation:

18.The capacitor in a capacitor start induction run ac motor is connected in series with 

  • AStarting winding
  • BRunning winding
  • CSquirrel cage winding
  • DCompensating winding 
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Answer:

Starting winding

Explanation:

19.A single-phase induction motor is provided with a 3- phase slip ring rotor connected to starting resistances. The motor would 

  • ANot start
  • BResult in more starting torque
  • CProduce no difference in the starting torque
  • DRun at half the synchronous speed
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Answer:

Result in more starting torque

Explanation:

20.Capacitor in a single-phase induction motor is used for 

  • AImproving the power factor
  • BImproving the starting torque
  • CStarting the motor
  • DReducing the harmonics
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Answer:

Starting the motor

Explanation: