DC Motor MCQ Questions & Answers

1.In the block diagram of a separately excited dc motor how does the armature induced emf appear as?

  • APositive feedback
  • BNegative feedback
  • CDisturbance input
  • DOutput 
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Answer:

Negative feedback

Explanation:

2.In a dc motor energy conversion would not have been possible but for

  • AInput energy from the supply
  • BProduction of back emf in the armature
  • CUse of commutator
  • DRotation of the machine
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Answer:

Production of back emf in the armature

Explanation:

3.The current drawn by a 120 V dc motor with back emf of 110 V and armature resistance of 0.4 ohm is

  • A4 A
  • B25 A
  • C275 A 
  • D300 A
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Answer:

25 A

Explanation:

4.A 220 V dc machine has an armature resistance of 1 ohm. If the full load current is 20 A , the difference of induced voltage, when the machine is running as a motor and generator is

  • A20 V
  • B0 V
  • C40 V
  • D60 V
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Answer:

40 V

Explanation:

5.The current drawn by a 220 V dc motor of armature resistance 0.5 ohm and back emf 200V is

  • A40 A
  • B44 A
  • C400 A
  • D440 A
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Answer:

40 A

Explanation:

6.With the increase in speed of a dc motor

  • ABoth back emf as well as line current increase
  • BBoth back emf as well as line current fall
  • CBack emf increases but line current falls
  • DBack emf falls and line current increases
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Answer:

Back emf increases but line current falls

Explanation:

7.If the back in a dc motor vanishes suddenly, the motor will

  • AStart hunting 
  • BBurn
  • CRun at very high speed
  • DRun at very slow speed
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Answer:

Burn

Explanation:

8.The output power of any electrical motor is taken from the

  • AArmature
  • BField
  • CCoupling mounted on the shaft
  • DMotor frame
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Answer:

Coupling mounted on the shaft

Explanation:

9.The armature shall must be able to withstand 

  • AAny unbalanced magnetic pull on the armature core
  • BTwisting strains due to transmission of torque 
  • CBending moment due to weight of the armature and commutator
  • DAll of the above 
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Answer:

All of the above 

Explanation:

10.The output indicated on the name plate of any motor is always the 

  • AGross power
  • BPower drawn in kVA
  • CPower drawn in kW
  • DOutput power at the shaft
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Answer:

Output power at the shaft

Explanation:

11.A thicker wire is used in dc series motor filed winding than that in a dc shunt motor.

  • ATo create more flux
  • BTo reduce resistance
  • CTo carry large load current
  • DBoth (b) and (c)
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Answer:

Both (b) and (c)

Explanation:

12.In case of a conductively compensated dc series motor, the compensating winding is provided

  • AIn series with the armature winding 
  • BIn parallel with the armature winding 
  • CIn parallel with the field winding
  • DAs a separate unit 
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Answer:

In series with the armature winding 

Explanation:

13.The dc compounded motors are generally 

  • ALevel compounded
  • BCumulative compounded
  • CDifferential compounded
  • DNone of these 
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Answer:

Cumulative compounded

Explanation:

14.In a dc compounded motor, the filed regulator is provided to

  • AControl the flux
  • BLimit the armature current 
  • CDemagnetize filed partially
  • DNone Of the above 
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Answer:

Control the flux

Explanation:

15.The direction of rotation of a dc motor can be determined by

  • AFleming’s right-hand rule
  • BFleming left hand rule
  • CLenz’s law
  • DAmpere law
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Answer:

Fleming left hand rule

Explanation:

16.The direction of rotation of a dc shunt motor can be reversed by interchanging 

  • AThe supply terminals
  • BThe filed terminals only
  • CThe armature terminals only
  • DEither field or armature terminals
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Answer:

Either field or armature terminals

Explanation:

17.When the supply terminals of a dc shunt motor are interchanged 

  • AThe motor will stop
  • BThe motor will run at its normal speed in the same direction as before
  • CThe direction of rotation will reverse
  • DThe motor will run much faster in the same direction
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Answer:

The motor will run at its normal speed in the same direction as before

Explanation:

18.The direction of rotation of a dc series motor can be reversed 

  • ABy interchanging supply terminals
  • BBy interchanging field terminals
  • CEither by interchanging supply terminals or by interchanging field terminals 
  • DBy interchanging supply terminals as well as field terminals
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Answer:

By interchanging field terminals

Explanation:

19.The speed of a dc motor is 

  • Adirectly proportional to back emf and flux
  • Bdirectly proportional to it back emf and inversely proportional to flux
  • Cinversely proportional to both back emf and flux
  • Ddirectly proportional to flux and inversely proportional to back emf
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Answer:

directly proportional to it back emf and inversely proportional to flux

Explanation:

20.If the load current and flux of a dc motor are held constant and voltage applied across it armature is increased by 54%, the speed of the motor will 

  • Aincrease by 5%
  • Breduce by 5%
  • Cremain un-alternated 
  • Ddepends on other factors 
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Answer:

increase by 5%

Explanation: