Hi Learners, in this article we have listed 60+ important MCQs on DC Motor which will be useful for your competitive exams, various interviews, viva, and other exams. The questions and answers are all collected from different exams and interviews of previous years.
You can also learn: Synchronous Motor: Working Principle, Types & Applications
These listed MCQs will be helpful for your conceptual clarity and preparation about DC Motor.
1. Effect of armature flux on the main flux in a d.c. motor is that
a) It makes a distribution of the flux density across both sections unequal
b) It inclines lines of force through the air gap such that they do not remain radial
c) Both (a) and (b)
d) None of these
Answer: c
2. For a series motor, field flux is
a) Proportional to temperature
b) Constant
c) Proportional to armature current
Answer: c
3. Speed of d.c. a series motor at no load is
a) 1500 rpm
b) 3000 rpm
c) Infinity
d) Zero
Answer: c
4. The function of the commutator in a d.c. the machine is
a) To change the alternating voltage to direct voltage
b) To change a.c. to d.c.
c) To improve commutation
d) For easy speed control
Answer: a
5. Field flux is constant in
a) Compound motor
b) Shunt motor
c) Series motor
d) None of these
Answer: c
6. Dummy coil in a d.c. the machine is used to
a) For the mechanical balance of the armature
b) Eliminate armature reaction
c) Eliminate reactance voltage
d) None of these
Answer: a
7. If back e.m.f. suddenly disappears in a d.c. motor
a) Motor will start the action as a generator
b) Motor will stop
c) Windings will burn due to high armature current
d) Nothing will happen
Answer: c
8. Four points in d.c. motor is used
a) To increase the field current
b) Not to affect the current through hold on coil even if any change in field current takes place
c) To increase the field current
d) None of these
Answer: b
9. Torque-speed characteristic of a series motor is
a) Parabola
b) Rectangular hyperbola
c) Linear
d) None of these
Answer: b
10. The direction of rotation of a d.c. series motor can be changed by interchanging
a) Field terminals
b) Voltage terminals
c) Both (a) and (b)
d) None of these
Answer: c
11. Use of the starter in d.c. motors are necessary because
a) They are not self-starting
b) To light the high initial current by inserting high resistance
c) To overcome back emf
d) None of these
Answer: b
12. For most of the application purposes
a) Depends on the requirement
b) Compound motor is used
c) Shunt motor is used
d) Series motor is used
Answer: a
13. Speed of a d.c. motor depends upon
a) Field flux
b) Armature resistance
c) Applied voltage
d) All of these
Answer: d
14. The armature winding of a series motor is excited
a) Resistively
b) Conductively
c) Inductively
d) None of these
Answer: b
15. Synchronous reactance is defined as reactance
a) Due to armature reaction and leakage of flux both
b) Due to the armature reaction of the machine
c) Due to leakage flux
d) Of synchronous machine
Answer: a
16. The torque produced by a series combination of two d.c. series motor is
a) Half the torque when they are connected in parallel
b) Twice the torque when they are connected in parallel
c) Four times the torque when they are connected in parallel
d) Equal to the torque when they are connected in parallel
Answer: c
17. In the series-parallel control method when two d.c. series motors are connected in series, the speed of the set is
a) Half of the speed of the motors
b) Rated speed of any of the motors
c) One-fourth of the speed of the motors
d) Same as in parallel
Answer: c
18. If the field current of a shunt motor is changed, then
a) Torque remains constant but h.p. will change
b) Horsepower remains constant but torque will change
c) Both remain constant
d) Both will change
Answer: b
19. If a d.c. the motor is connected across a.c. supply, the motor will
a) Run at a lower speed
b) Burn
c) Run at normal speed
d) Run continuously but for sparking at brushes
Answer: b
20. Shunt motor has
a) Low speed at high loads and high speed at low loads
b) Low speed at low loads and high speed at low loads
c) Widely varying speed
d) Constant speed
Answer: d
21. In the field flux method of speed control
a) Any speed can be attained
b) Speeds above normal speed can be attained
c) Speeds below normal speed can be attained
d) None of these
Answer: b
22. Speed of the d.c. motor can be varied by
a) Varying armature resistance
b) Varying supply voltage
c) Either (a) or (b)
d) Varying field current
Answer: c
23. Dynamic braking is generally used for
a) Shunt motors
b) Compound motors
c) Series motors
d) All of these
Answer: d
24. Stalling current is the maximum value of
a) Load current for which speed is zero
b) Field current for which speed is maximum
c) Load current for which speed is maximum
d) Diverter current for which speed is maximum
Answer: c
25. Torque developed in d.c. motor depends on
a) Armature
b) Speed
c) Magnetic field
d) Both (a) and (c)
Answer: d
26. As the load is increased, the speed of d.c. shunt motor will
a) Increase Slightly
b) Reduce slightly
c) Remains constant
d) None of these
Answer: b
27 Which method of speed control has minimum efficiency?
a) Field control method
b) Voltage control method
c) Armature control method
d) None of these
Answer: c
28. Field flux of d.c. motor can be controlled to
a) Steady speed
b) Speeds above-rated speed
c) Speeds below-rated speed
d) Speeds above and below rated speed
Answer: b
29. Ward-Leonard method of speed control is basically usefully where usually
a) a wide range of sensitive speed control is required
b) a wide range of speed control is required
c) narrow range of speed control is required
d) none of these
Answer: a
30. In the ward-Leonard system, the minimum number of machines required are
a) two
b) three
c) four
d) five
Answer: b
31. Ward-Leonard method is basically a
a) field diverter method
b) field control method
c) armature resistance control method
d) voltage control method
Answer: d
32. Speed regulation of a d.c. motor can be ideally achieved with
a) A.C. excitation to the field of the motor
b) Variable excitation to the field of the motor
c) constant excitation to the field of the motor
d) no excitation to the field of the motor
Answer: c
33. A disadvantage of the field-control method of speed control is
a) That speed above normal speed can be achieved
b) That commutation becomes unsatisfactory
c) Its low efficiency
d) None of these
Answer: b
34. If plugging is applied to a series motor for a long time, then
a) It will start revolving in another direction at a low speed
b) Motor will stop
c) Motor will burn
d) None of these
Answer: a
35. The fully load current of a 20 HP 500 V dc motor will be closer to
a) 15 A
b) 35 A
c) 60 A
d) 100 A
Answer: b
36. The speed of a series-wound dc motor
a) cannot be controlled by the diverter
b) can be controlled by a shunt field regulator
c) increases as armature circuit resistance increases
d) increases as flux decreases
Answer: d
37. An electric motor may give noise due to
a) cooling air
b) defective bearing
c) magnetic effect
d) all of the above
Answer: d
38. A dc motor having full load speed of 800 and speed regulation of 8% will have no load speed of
a) 736 rpm
b) 768 rpm
c) 864 rpm
d) 832 rpm
Answer: c
39. If conditions for maximum power for a dc motor are established, the efficiency of the motor will be
a) 100%
b) 90 to 95%
c) 81%
d) Less than 50%
Answer: d
40. The speed of a dc motor is
a) always constant
b) directly proportional to back e.m.f.
c) directly proportional to flux
d) inversely proportional to the product of back e.m.f. and flux
Answer: b
41. The ratio of starting torque to fully load torque is least in case of
a) shunt motors
b) series motors
c) compound motors
d) none
Answer: a
42. In a dc series motor, shaft torque is less than the armature torque due to
a) stray losses
b) eddy current losses
c) hysteresis losses
d) all of the above
Answer: a
43. Dc motor with self-loading properties is
a) shunt motor
b) series motor
c) differentially compound motor
d) cumulatively compound motor
Answer: c
44. Which motor will have the least percentage increases of input current for the same percentage increases in torque?
A) shunt motor
B) series motor
C) separately excited motor
D) cumulatively compound motors.
Answer: b
45. The mechanical power developed by a dc motor is maximum when the ratio of back emf/applied voltage is
A) 0.7
B) 0.5
C) 3.0
D) 1.0
Answer: b
46. If the load current and flux of a dc motor are held constant and voltage applied across its armature is increased by 5 percent, the peed of motor will be
a) increases by about 5%
b) reduce by about 5%
c) remain unaltered
d) depend on other factors
Answer: a
47. A dc motor develops a torque of 140 N-m at 1400 rpm. If the motor now runs at 1000 rpm, the torque developed will be
a) 51 N-m
b) 71 N-m
c) 1000 N-m
d) 196 N-m
Answer: d
48. In a dc shunt motor if the supply voltage is increased by 10%, which of the following will increase?
a) Full load speed
b) Full load current
c) Starting torque
d) All of the above
Answer: a
49. The type of dc motor control preferred for applications where unusually wide and very sensitive speed control is required will be
a) Flux control
b) Voltage control
c) Ward-Leonard control
d) Armature control
Answer: c
50. The relationship between back emf and applied voltage in case of a dc motor is given by
a) Eb= 2 V – IaRa
b) Eb= 2 V + IaRa
c) Eb = V – IaRa
d) Eb = V + IaRa
Answer: c
51. The magnetic mechanical force in a dc motor is dependent on
a) cross-section area of the conductor
b) length of the conductor
c) nature of the material of the conductor
d) none of these
Answer: b
Also check: Only 60 MCQs on 3-Phase Induction Motor (Helpful)
52. The current drawn by a dc motor at the starting instant will be
A) V/Ra
B) Eb/Ra
C) V/2Ra
D) 2 V/Ra
Answer: a
53. If the back emf in a dc motor vanishes suddenly, the motor will
a) run at a very low speed
b) run at a very high speed
c) burn
d) start hunting
Answer: c
54. The maximum speed ratio obtainable in a Ward Leonard control, the dc motor is
a) 2:1
b) 5:1
c) 25:1
d) 250:1
Answer: c
55. A dc motor can be easily identified by looking at
a) yoke
b) commutator
c) winding
d) frame
Answer: b
56. If the flux of dc motor approaches zero
a) the motor will tend to run at an infinite speed
b) the motor will stop
c) its speed will remain unchanged
d) its speed will approach zero
Answer: a
57. In a rotating electric machine, the torque produced will be maximum when
a) torque angle is zero
b) torque angle is 90o
c) two magnetic fields are aligned with each other
d) field strength are maximum and torque angle is zero
Answer: b
58. For the operation of the milling machine, the following motor is used
a) DC short shunt compound motor
b) DC compound motor
c) DC shunt motor
d) DC series motor
Answer: c
59. In Ward, Leonard controls the lower limit of speed is imposed by
a) core losses of the motor
b) residual magnetism of the generator
c) mechanical losses of motor and generator together
d) all of the above
Answer: b
60. If the applied voltage of a dc shunt motor is halved with the load torque doubled, the armature current will be
a) halved
b) zero
c) unaltered
d) doubled
Answer: d
61. Change in the speed of a motor, under Ward Leonard’s control, occurs due to change in
a) armature voltage of dc motor
b) armature current of dc motor
c) field excitation of dc motor
d) supply voltage
Answer: a
62. The starting resistance of a dc motor is usually
a) low
b) around 100 ohms
c) very large
d) infinitely large
Answer: a
63. A dc shunt motor is running at light load. What will happen if the field winding gets opened?
a) motor will stop
b) motor will burn
c) motor will pick up high-speed
d) motor will make noise
Answer: c
64. The speed-torque characteristic of a series motor is a/an
a) Hyperbola
b) Ellipse
c) Parabola
d) Circle
Answer: a
65. For which application a dc motor is preferred over an ac motor?
a) Fixed speed operation
b) Variable speed operation
c) High-speed operation
d) Low-speed operation
Answer: b
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