DC Motor MCQ Questions & Answers

DC Motor  MCQ Question and Answer

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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Correct Answer : (B)

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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Correct Answer : (B)

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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Correct Answer : (B)

25 A

Explanation:

The current drawn by a 120 V dc motor with back emf of 110 V and armature resistance of 0.4 ohm is 25 A.

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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Correct Answer : (C)

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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Correct Answer : (A)

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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Correct Answer : (C)

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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Correct Answer : (B)

Burn

Explanation:

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

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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Correct Answer : (C)

Coupling mounted on the shaft

Explanation:

9.The armature shaft 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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Correct Answer : (D)

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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Correct Answer : (D)

Output power at the shaft

Explanation:

The output indicated on the name plate of any motor is always the  Output power at the shaft.

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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Correct Answer : (D)

Both (b) and (c)

Explanation:

A thicker wire is used in dc series motor filed winding than that in a dc shunt motor To reduce resistance and to carry large load current.

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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Correct Answer : (A)

In series with the armature winding 

Explanation:

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

13.The dc compounded motors are generally 

  • ALevel compounded
  • BCumulative compounded
  • CDifferential compounded
  • DNone of these 
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Correct Answer : (B)

Cumulative compounded

Explanation:

The dc compounded motors are generally Cumulative compounded motor.

14.In a dc compound 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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Correct Answer : (A)

Control the flux

Explanation:

In a dc compound motor, the filed regulator is provided to Control the flux.

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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Correct Answer : (B)

Fleming left hand rule

Explanation:

The direction of rotation of a dc motor can be determined by Fleming left hand rule.

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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Correct Answer : (D)

Either field or armature terminals

Explanation:

The direction of rotation of a dc shunt motor can be reversed by interchanging Either field or armature terminals.

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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Correct Answer : (B)

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

Explanation:

When the supply terminals of a dc shunt motor are interchanged, the motor will run at its normal speed in the same direction as before.

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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Correct Answer : (B)

By interchanging field terminals

Explanation:

The direction of rotation of a dc series motor can be reversed By interchanging field terminals.

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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Correct Answer : (B)

directly proportional to it back emf and inversely proportional to flux

Explanation:

The speed of a dc motor is directly proportional to it back emf and inversely proportional to flux.

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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Correct Answer : (A)

increase by 5%

Explanation: