175+ DC Motors Objective Questions and Answers

In this article, we shared the DC motors objective questions and answers for electrical and electronics engineers.

DC Motors Objective Questions

DC Motors Objective Questions and Answers

The below list provides all the multiple-choice questions related to DC motor.

Answers are available at the bottom of the article.

1. According to Fleming’s left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of

A)current, in the conductor
B)movement of conductor
C)none of these answers
D)the resultant force on the conductor

2. In a D.C. shunt motor, speed is

A)proportional to the square of the current
B)inversely proportional to the armature current
C)independent of armature current
D)directly proportional to the armature current

3. In variable speed motor

A)same commutating field is needed at low speed than at high speed
B)a stronger commutating field is needed at low speed than at high speed
C)none of these answers
D)a weaker commutating field is needed at low speed than at higt speed

4. The generated e.m.f. and the current are in the opposite direction in the case of

A)d.c. motors
B)none of these answers
C)d.c. generators
D)both d.c. generators and d.c. motors

5. In a D.C. generator, the iron losses mainly take place in

A)yoke
B)armature rotor
C)commutator
D)armature conductors

6. In a D.C. motor constant torque is produced due to

A)pole shoes
B)end-plates
C)rotor laminations
D)commutator

7. Speed control by the variation of flux, in a D.C. shunt motor, will give

A)constant torque drive
B)variable torque drive
C)constant power drive
D)variable power drive

8. What will happen if supply terminals of D.C. shunt motor are interchanged?

A)Motor will run at its normal speed in the same direction as it was running
B)Motor will run at speed lower than the normal speed in the same direction
C)Motor will stop
D)The direction of rotation will reverse

9. A series motor is started without load. The effect is that

A)the speed increases rapidly
B)the torque increases rapidly
C)the current drawn increases rapidly
D)the back e.m.f. decreases

10. Which of the following methods is most effective in finding out the no-load losses in a large D.C. shunt motor?

A)Ward-Leonard test
B)Block rotor test
C)Hopkinson’s test
D)Swinburne’s test
E)Field’s test

11. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of

A)induction motor
B)D.C. shunt motor
C)all of these answers
D)D.C. series motor

12. Which of the following motors one will choose to drive the rotary compressor?

A)Synchronous motor
B)D.C. shunt motor
C)Universal motor
D)D.C. series motor

13. The plugging gives the

A)smallest torque braking
B)zero torque braking
C)none of these answers
D)highest torque braking

14. Which of the following loss in a D.C. generator varies significantly with the load current?

A)Windage loss
B)Field copper loss
C)None of these answers
D)Armature copper loss

15. Why are the D.C. motors preferred for traction applications?

A)Torque and speed are inversely proportional to armature current
B)Torque is proportional to armature current
C)The speed is inversely proportional to the torque and the torque is proportional to square of armature current
D)Torque is proportional to square root of armature current

16. Which of the following D.C. motors has the least drop in speed between no-load and nominal load?

A)Shunt motor with commutating pole
B)Compound motor without commutating poles
C)Series motor without commutating poles
D)Series motor with commutating poles

17. Which of the following can be used to control the speed of a D.C. motor?

A)Thermistor
B)Transistor
C)Thyristor
D)Thyratron

18. Which of the following application requires high starting torque?

A)Locomotive
B)Air blower
C)Lathe machine
D)Centrifugal pump

19. Which of the following can be used for controlling the speed of a D.C. motor?

A)Thyratron
B)Thermistor
C)Thyristor
D)Transistor

20. If the terminals of armature of the D.C. motor are interchanged, this action will offer the following kind of braking

A)none of the answers
B)any of these answers
C)regenerative
D)plugging
E)dynamic braking

21. Which of the following load normally needs starting torque more than the rated torque?

A)Blowers
B)Air compressors
C)Conveyors
D)Centrifugal pumps

22. A face plate starter is employed for starting

A)synchronous motor
B)induction motor
C)d.c. series motor
D)universal motor

23. The losses occurring in a D.C. generator are given below. Which loss is likely to have the least proportion?

A)Armature copper losses
B)Mechanical losses
C)Magnetic losses
D)Field copper losses

24. The armature shaft of a D.C. motor must be able to withstand

A)twisting strains due to transmission of torque
B)any unbalanced magnetic pull on the armature core
C)all of these answers
D)bending moment due to the weight of the armature and commutator

25. Which of the following methods of braking is used in rolling mills?

A)Regenerative braking
B)Plugging
C)Dynamic braking
D)Mechanical brakes

26. Speed control by varying the armature circuit resistance, in a D.C. motor, provides a

A)constant torque drive
B)variable power drive
C)variable torque drive
D)constant power drive

27. The power mentioned on the nameplate of an electric motor indicates

A)the power is drawn in kW
B)the power is drawn in kVA
C)the gross power
D)the output power available at the shaft

28. Voltage equation for D.C. motor is

A)V = Eb -​​ IaRa
B)Eb = V + ​​IaRa
C)Eb = V -​​ Ia2Ra
D)V = Eb +​​ IaRa

29. Which of the following motors have almost constant speed over their full load range?

A)D.C. series motors
B)A.C. series motors
C)Both D.C. shunt motors and Low resistance squirrel cage motors
D)D.C. shunt motors
E)Low resistance squirrel cage motors

30. As there is no back e.m.f. at the instant of starting, a D.C. motor, in order to prevent a heavy current from flowing through the armature circuit

A)a high value resistor is connected across the field winding
B)a resistance is connected in series with armature
C)a resistance is connected parallel to the armature
D)armature is temporarily open circuited

31. Which of the following motor has high starting torque?

A)Induction motor
B)D.C. series motor
C)A.C. series motor
D)Synchronous motor

32. Which D.C. motor Will have the least percentage increase of input current for the same percentage increase in the torque?

A)Separately excited motor
B)Cumulative compound motor
C)Shunt motor
D)Series motor

33. When the electric train is moving down a hill the D.C. motor act as

A)D.C. shunt motor
B)D.C. shunt generator
C)D.C. series generator
D)D.C. series motor

34. In electric motors carbon brushes are used to

A)prevent sparking during commutation
B)prevent overheating of armature windings
C)provide a path for the flow of current
D)brush off carbon deposits on the commutator

35. Between Field’s test and Hopkinson’s test the main common thing is that both

A)are regenerative tests
B)use negligible power
C)need two similar mechanically coupled motors
D)need two electrically coupled series motors

36. Speed control of a cumulatively compounded D.C. motor can be effected through the change of

A)armature voltage
B)armature resistance
C)field resistance
D)any of these answers

37. Which D.C. motor has got maximum self-relieving property?

A)Cumulatively compounded motor
B)Differentially compounded motor
C)Shunt motor
D)Series motor

38. A wide and very sensitive speed control is usually required in case of

A)elevators
B)all of these answers
C)colliery winders
D)steel rolling mills

39. If the field circuit of a loaded shunt motor is suddenly opened

A)it would draw abnormally high armature current
B)it would race to almost infinite speed
C)torque developed by the motor would be reduced to zero
D)the fuse or circuit breaker will open the circuit before too much damage is done to the motor

40. The speed of a D.C. motor can be varied by varying

A)applied voltage
B)any of these answers
C)resistance in series with the armature
D)field current

41. The direction of rotation of a D.C. series motor can be changed by

A)either of interchanging supply terminals and interchanging field terminals
B)interchanging field terminals
C)interchanging supply terminals
D)None of these answers

42. In the case of D.C. shunt motors the speed is dependent on the back e.m.f. only because

A)flux is proportional to armature current
B)back e.m.f. is equal to armature drop
C)flux is practically constant in ac. shunt motors
D)armature drop is negligible

43. If Ia ​​be the armature current, then the speed of a D.C. shunt motor is

A)varies as 1 /​​ Ia
B)proportional to​​ Ia
C)independent of​​ Ia
D)varies as (​​Ia)2

44. D.C. generators are normally designed for maximum efficiency around

A)all of these answers
B)rated r.p.m.
C)full-load
D)rated voltage

45. The total losses in a well designed D.C. generator of 10 kW will be nearly

A)100 W
B)1500 W
C)500 W
D)1000 W

46. In a D.C. motor, unidirectional torque is produced with the help of

A)bushes
B)both bushes and commutator
C)end plates
D)commutator

47. For which of the following applications a D.C. motor is preferred over an A.C. motor?

A)Variable speed operation
B)High speed operation
C)Low speed operation
D)Fixed speed operation

48. Which of the following motor has the poorest speed regulation?

A)Differential compound motor
B)Cumulative compound motor
C)Shunt motor
D)Series motor

49. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to

A)100% of the previous value
B)25% of the previous value
C)50% of the previous value
D)10% of the previous value
E)none of these answers

50. In the hazardous areas of gassy mines, material transportation is done by vehicles powered by

A)batteries
B)I.C. engines
C)D.C. mains
D)A.C. mains

51. Which of the following statement is incorrect? If a starter is not used with a large D.C. motor, it will draw a starting current which

A)is many times its full-load current
B)will produce very low starting torque
C)will produce an excessive line voltage drop
D)will damage the commutator

52. These days D.C. motors are widely used in

A)electric traction
B)machine shops
C)pumping sets
D)air compressors

53. Which D.C. motor has got maximum self loading property?

A)Cumulatively compounded motor
B)Differentially compounded motor
C)Series motor
D)Shunt motor

54. Compensating winding in a D.C. machine is placed

A)on yoke in the interpolar gap
B)on yoke in the pole faces
C)on armature
D)none of these answers

55. A direct online starter is used for starting motors

A)up to 10 H.P.
B)up to 15 H.P.
C)up to 5 H.P.
D)up to 20 H.P.

56. In a D.C. motor, the ratio Eb/Va indicates

A)running torque of the motor
B)the efficiency of the motor
C)speed regulation of the motor
D)starting torque of the motor

57. The condition for maximum power in case of D.C. motor is

A)supply voltage = 1/2 x back e.m.f.
B)back e.m.f. = 1/2 x supply voltage
C)supply voltage = back e.m.f.
D)back e.m.f. = 2 x supply voltage

58. Which of the following motor is used in the locomotives motor drives?

A)A.C. series motor
B)D.C. series motor
C)Synchronous motor
D)Induction motor

59. For constant torque drive which speed control method is preferred?

A)Field control
B)Armature voltage control
C)Shunt armature control
D)Mechanical loading system

60. The variable resistor shunting the field of a D.C. series motor is called a

A)field divertor
B)armature divertor
C)potential divider
D)voltage regulator

61. In Ward-Leonard control the lower limit of speed is imposed by

A)mechanical losses of motor and generator together
B)core losses of motor
C)all of these answers
D)residual magnetism of the generator

62. The speed of a D.C. series motor is

A)proportional to the armature current
B)proportional to field current
C)proportional to the square of the armature current
D)inversely proportional to the armature current

63. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will

A)increase four folds
B)be doubled
C)reduce to one-fourth value
D)remain unchanged

64. At the instant of starting when a D.C. motor is put on supply, it behaves like

A)a low resistance circuit
B)a highly resistive circuit
C)a capacitive circuit
D)none of these answers

65. All motors, basically, operate on the principle of either repulsion or

A)electro-magnetism
B)semi-conduction
C)induction
D)capacitance

66. The main disadvantage of Hopkinson’s test for finding efficiency of the shunt D.C. motors is that it

A)needs one motor and one generator
B)ignores any change in iron loss
C)requires full-load power
D)requires two identical shunt machines

67. In electric motors carbon brushes are used to

A)provide a path for flow of current
B)prevent overheating of armature windings
C)prevent sparking during commutation
D)brush off carbon deposits on the commutator

68. In D.C. machines the residual magnetism is of the order of

A)10 to 15 percent
B)50 to 75 percent
C)2 to 3 percent
D)20 to 25 percent

69. The armature torque of the D.C. shunt motor is proportional to

A)both field flux only and armature current only
B)armature current only
C)none of these answers
D)field flux only

70. Which of the following motor is preferred for operation in a highly explosive atmosphere?

A)Series motor
B)Air motor
C)Battery operated motor
D)Shunt motor

71. A series motor is best suited for driving

A)cranes and hoists
B)none of these answers
C)machine tools
D)shear and punches

72. The operation of electric generators and motors depends on the interaction between magnetic field and

A)electric current
B)commutator
C)electric field
D)copper conductors

73. Sparking at the commutator of a D.C. motor may result in

A)damage to commutator segments
B)all of these answers
C)increased power consumption
D)damage to commutator insulation

74. When two D.C. series motors are connected in parallel, the resultant speed is

A)normal speed
B)zero
C)less than the normal speed
D)more than the normal speed

75. If conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be

A)80 to 90%
B)60 to 70%
C)less than 50%
D)1

76. Which of the following losses are significantly reduced by laminating the core of a D.C. generator?

A)Eddy current losses
B)Windage losses
C)Hysteresis losses
D)Copper losses

77. The purpose of retardation test on D.C. shunt machines is to find out

A)eddy current losses
B)field copper losses
C)stray losses
D)windage losses

78. Which of the following loss in a D.C. generator is dissipated in the form of heat?

A)Mechanical loss
B)All of these answers
C)Copper loss
D)Core loss

79. Ward-Leonard control is basically a

A)field diverter method
B)armature resistance control method
C)voltage control method
D)field control method

80. The simplest form of a motor controller is

A)toggle switch
B)relay
C)magnetic switch
D)drum switch

81. In Ward Leonard method of speed control of a D.C. motor, change in speed of the motor is obtained by the

A)change in armature current of D.C. motor
B)change in the field excitation of the D.C. motor
C)change in armature voltage of D.C. motor
D)change in supply voltage

82. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven

A)does not run as a generator
B)comes to stop after sometime
C)also runs as a motor
D)runs as a generator

83. A D.C. series motor, as compared to shunt and compound motors, has the highest torque at the start because of its comparatively

A)large armature current
B)lower armature resistance
C)stronger series field
D)fewer series turns

84. If​​ Bmax is the maximum flux density, then eddy current loss will vary as

A)​​Bmax
B)​​(Bmax)1.2
C)​​​​(Bmax)2
D)​​​​(Bmax)2.4

85. A D.C. motor can be easily identified by

A)size of conductor
B)commutator
C)winding
D)yoke

86. A 230 V D.C. shunt motor takes 32 A at full load. The back e.m.f. on full load, if the resistance of motor armature and shunt field windings are 0.2 Ω and 115 Ω respectively, will be

A)215 V
B)224 V
C)220 V
D)210 V

87. The type of D.C. motor used for shears and punches is

A)series motor
B)differential compound D.C. motor
C)cumulative compound D.C. motor
D)shunt motor.

88. Torque developed by a D.C. motor depends upon

A)all of these answers
B)radius of armature
C)number of conductors
D)the active length of the conductor
E)current flow through the conductors

89. Usually wide and sensitive speed control is desired in the case of

A)steel rolling mills
B)colliery winders
C)elevators
D)centrifugal pumps

90. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by

A)decreasing the armature current
B)none of these answers
C)reducing the field current
D)increasing the armature current
E)increasing the excitation current

91. Which of the following tests can be conducted on all types of D.C. machines?

A)Brake test
B)Block rotor test
C)Field’s test
D)Hopkinson’s test
E)Running down test

92. The speed of a D.C. motor, under constant load conditions, is affected by

A)back e.m.f.
B)none of these answers
C)armature current
D)field flux

93. If the no-voltage release of a D.C. motor starter fails to work on the resumption of supply after a break, the motor will

A)develop very low torque
B)not start automatically
C)get damaged
D)start automatically without trouble

94. If a D.C. motor is to be selected for conveyors, which motor would be preferred?

A)Shunt motor
B)Cumulative compound motor
C)Differentially compound motor
D)Series motor

95. Which of the following motors is most suitable for signaling devices and many kinds of timers?

A)D.C. shunt motor
B)D.C. series motor
C)Induction motor
D)Reluctance motor

96. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be

A)almost negligible
B)more than full-load current
C)rated full-load current
D)less than full-load current

97. The speed of a D.C. shunt motor more than its full-load speed can be obtained by

A)decreasing the field current
B)increasing the field current
C)decreasing the armature current
D)increasing the armature current

98. In a motor, energy conversion would not have been possible but for the

A)input energy from supply
B)use of commutator
C)production of opposing back e.m.f. Eb ​​in the armature
D)application of Fleming’s left-hand rule

99. Which D.C. motor will be preferred for machine tools?

A)Differential compound motor
B)Series motor
C)Shunt motor
D)Cumulative compound motor

100. The rated speed of a given D.C. shunt motor is 900 r.p.m. To run this machine at 1000 r.p.m., which of the following speed control scheme will be used?

A)Ward-leonard control
B)None of these answers
C)Field resistance control
D)Armature current resistance control

101. D.C. shunt motors are used for driving

A)cranes
B)machine tools
C)trains
D)hoists

102. When the armature of a D.C. motor rotates, e.m.f. induced is

A)none of these answers
B)mutually induced e.m.f.
C)back e.m.f.
D)self-induced e.m.f.

103. If a D.C. shunt motor is working at no load and if the shunt field circuit suddenly opens

A)motor will run at very slow speed
B)this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
C)nothing will happen to the motor
D)this will make armature to take heavy current, possibly burning it

104. In which of the following tests only one motor is required?

A)Swinburne’s test
B)Brake test
C)Hopkinson’s test
D)Field’s test

105. Three point starter can be used for

A)both shunt and compound motor
B)shunt motor only
C)series motor only
D)compound motor only

106. A motor for punching machine is usually subjected to

A)no load
B)intermittent load
C)continuous full load
D)continuous part load

107. A brake test on D.C. motors is usually restricted to

A)variable speed motors
B)small horse power motors
C)open frame type motors.
D)high speed motors

108. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will

A)become zero
B)remain same
C)increase
D)decrease

109. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity?

A)Brake test
B)Swinburne’s test
C)Hopkinson’s test
D)Field test

110. In the case of conductively compensated D.C. series motors, the compensating winding is provided

A)in series with armature winding
B)in parallel with field winding
C)as separately wound unit
D)in parallel with the armature winding

111. Which D.C. motor is preferred for elevators?

A)Series motor
B)Cumulative compound motor
C)Differential compound motor
D)Shunt motor

112. If the supply voltage for a D.C. motor is increased, which of the following will decrease ?

A)Full-load current
B)Operating speed
C)All of these answers
D)Starting torque

113. While starting a differential compound motor, it is best to short the series field in order to avoid

A)motor starting in wrong direction
B)excessive starting period
C)large in rush of current
D)tripping of the circuit breaker

114. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for a short duration.

A)compound motor
B)series motor
C)shunt motor
D)any of these answers

115. In a D.C. generator, all of the following could be the effects of iron losses except

A)Increase in terminal voltage
B)Rise in temperature of ventilating air
C)Loss of efficiency
D)Excessive heating of core

116. To get the speed of the D.C. motor below the normal without wastage of electrical energy ____ is used.

A)none of these answers
B)Ward Leonard control
C)rheostatic control
D)either rheostatic control or Ward Leonard control

117. In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be

A)around 90%
B)anywhere between 75% and 90%
C)1
D)less than 50%

118. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?

A)Frame
B)Commutator
C)Shaft
D)Stator

119. The function of a field regulator for compound motors is to

A)demagnetize the field partially
B)control the flux
C)none of these answers
D)limit the armature current

120. Which motor should be used for centrifugal pumps?

A)Shunt motor
B)Series motor
C)Either Series motor or Shunt motor
D)None of these answers

121. The hysteresis loss in a D.C. generator varies with the frequency of magnetic reversals as

A)​​f1.6
B)​​1/6
C)​​​​f2
D)​​f

122. The condition for maximum efficiency for a D.C. generator is

A)eddy current losses = stray losses
B)hysteresis losses = eddy current losses
C)variable losses = constant losses
D)copper losses = 0

123. Which of the following law/rule can be used to determine the direction of rotation of D.C. motor?

A)Faraday’s law
B)Lenz’s law
C)Coloumb’s law
D)Fleming’s left-hand rule

124. Which of the following motor has high starting torque?

A)D.C. series motor
B)Synchronous motor
C)A.C. series motor
D)none of these answers

125. Which loss in a D.C. generator does not vary with the load as well as flux density?

A)Copper loss
B)Hysteresis loss
C)Eddy current loss
D)Windage loss

126. Which of the following motors, on the removal of load, will run at the highest speed?

A)Shunt motor
B)Cumulative compound
C)Differential compound
D)Series motor

127. In D.C. shunt motors as load are reduced

A)the speed will remain almost constant
B)the speed will reduce
C)the speed will increase abruptly
D)the speed will increase in proportion to reduction in load

128. Which of the following, in a D.C. motor, can sustain the maximum temperature rise?

A)Armature windings
B)Field windings
C)Slip rings
D)Commutator

129. A three point starter is considered suitable for

A)all D.C. motors
B)shunt motors
C)shunt, compound and series motors
D)shunt as well as compound motors

130. In a D.C. motor if the back e.m.f. is absent

A)motor will burn
B)motor will run at very slow speed
C)motor will not run at all
D)motor will run at very high speed

131. A D.C. series motor is that which

A)can be started easily without load
B)has a poor torque
C)has almost constant speed
D)has its field winding consisting of thick wire and less turns

132. D.C. generators are installed near the load centers to reduce

A)sparking
B)corona losses
C)line losses
D)iron losses

133. In Field’s test for series motors, one motor drives the other machine as

A)differential compound generator
B)series generator
C)separately excited generator
D)cumulative compound generator

134. If the speed of a D.C. shunt motor is increased the back e.m.f. of the motor will

A)become zero
B)decrease
C)increase
D)remain same

135. Differentially compound D.C. motors can find applications requiring

A)low starting torque
B)variable speed
C)frequent on-off cycles
D)high starting torque

136. If a D.C. motor is connected across the A.C. supply it will

A)run at normal speed
B)burn due to heat produced in the field winding by eddy currents
C)not run
D)run at lower Speed

137. In a manual shunt motor starter

A)overload relay is connected in series and no volt relay in parallel with the load
B)overload relay and no volt relay are both connected in parallel with the load
C)overload relay is connected in parallel and no volt relay in series with the load
D)overload relay and no volt relay are both connected in series with the load

138. When the speed of a D.C. motor increases

A)back e.m.f. increases and current drawn decreases
B)back e.m.f. as well as current drawn both decrease
C)back e.m.f. decreases and current drawn increases
D)back e.m.f. as well as current drawn both increase

139. Starters are used with D.C. motors because

A)these motors have high starting torque
B)to restrict armature current as there is no back e.m.f. while starting
C)back e.m.f. of these motors is zero initially
D)these motors are not self-starting

140. Which loss in a D.C. generator varies with load?

A)Copper loss
B)Windage loss
C)Eddy current loss
D)Hysteresis loss

141. For a D.C. shunt motor if the excitation is changed

A)torque, power and speed, all will change
B)torque will remain constant
C)torque will change but power will remain constant
D)torque and power both will change

142. D.C. motor is to drive a load which is almost nil for certain part of the load cycle and peak value for a short duration. We will select this

A)any of these answers
B)series motor
C)shunt motor
D)compound motor

143. A shearing machine has a cyclic load consisting of intermittent light and henry loads. Which of the following D.C. motor will be suitable for this purpose?

A)Series motor
B)Differential compound motor
C)Shunt motor
D)Cumulative compound motor

144. Which D.C. motor will be preferred for constant speed line shafting ?

A)Shunt motor
B)Cumulative compound motor
C)Series motor
D)Differentially compound motor

145. The hysteresis loss in a D.C. machine least depends on

A)Volume and grade of iron
B)Maximum value of flux density
C)Frequency of magnetic reversals
D)Rate of flow of ventilating air

146. The losses occurring in a D.C. generator are given below. Which loss is likely to have the highest proportion at rated load of the generator?

A)armature copper loss
B)eddy current loss
C)hysteresis loss
D)field copper loss

147. Which one of the following is not the function of pole shoes in a D.C. machine?

A)To spread out flux for better uniformity
B)To reduce eddy current loss
C)To reduce the reluctance of the magnetic path
D)To support the field coils

148. Which of the following statements is correct, in the case of a D.C. series motor?

A)It cannot be used where high starting torque is required
B)It should be directly connected to the load
C)It may run away if its field becomes open
D)It is a constant speed motor

149. Which of the following tests can be used to determine no-load losses in a D.C. shunt motor?

A)Swinburne’s test
B)Running down test
C)Field test
D)Brake test

150. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?

A)The armature may burn
B)The motor will stop
C)The motor will continue to run
D)The motor will run noisy

151. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing, and speed control

A)four point starter is used
B)all of these answers
C)drum type controller is used
D)three point starter is used

152. In the case of a shunt motor if the supply voltage is increased by 10%, which of the following will decrease?

A)starting torque
B)none of these answers
C)full load speed
D)full load current

153. Sparking is discouraged in a D.C. motor because

A)it increases the input power consumption
B)commutator gets damaged
C)none of these answers
D)both it increases the input power consumption and commutator gets damaged

154. Which of the following steps is likely to result in a reduction of hysteresis loss in a D.C. generator?

A)Providing laminations in armature core
B)Using non-magnetic material for frame
C)Providing laminations in stator
D)Using material of low hysteresis coefficient for armature core material

155. In regenerative braking

A)motor energy is dissipated in armature heating
B)motor energy is dissipated as heat
C)motor energy is dissipated in windage losses
D)motor is made to run as a generator

156. Regenerative braking on shunt motors is used when

A)the load is variable
B)the load is constantly decreasing
C)the load acts as a braking force
D)the load has overhauling characteristics.

157. Which of the following loss of D.C. motor decreases with increase in load?

A)Friction and windage loss
B)Brush contact loss
C)Core loss
D)none of these answers

158. Which of the following methods is most economical fol. finding the no-load losses of a large D.C. shunt motor?

A)Retardation test
B)Hopkinson’s test
C)Swinburne’s test
D)none of these answers

159. If​ Ta ​is the torque and​ Ia ​is the armature current for a D.C. motor, then which of the following relation is valid before saturation ?

A)Ta ​​∝​​ Ia
B)Ta ​​​​∝ I /​​ Ia ​​
C)Ta ​​​​∝​​ Ia2
D)​​Ta ​​∝​​ Ia2

160. As compared to an induction motor, the air gap in a D.C. motor is

A)less than 50%
B)same
C)between 50% and 90%
D)more

161. If a D.C. shunt motor is working at full load and if the shunt field circuit suddenly opens

A)this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
B)this will make armature to take heavy current, possibly burning it
C)nothing will happen to motor
D)motor will come to stop

162. Following motor is used where high starting torque and wide speed range control is required.

A)D.C. motor
B)Single phase capacitor start
C)None of these answers
D)Induction motor
E)Synchronous motor

163. D.C. series machine has field consisting of

A)many number of turns of thick wire
B)many number of turns of thin wire
C)few number of turns of thin wire
D)few number of turns of thick wire

164. Which motor should not be started on no-load?

A)Differentially compounded motor
B)Cumulatively compounded motor
C)Series motor
D)Shunt motor

165. The armature voltage control of the D.C. motor provides

A)constant voltage drive
B)none of these answers
C)constant torque drive
D)constant current drive

166. Regenerative braking on D.C. shunt motors is used when

A)the load has overhauling characteristics
B)the load is constantly decreasing
C)the load also acts as a braking force
D)the load is variable

167. Which of the following is not necessarily the advantage of D.C. motors over A.C. motors?

A)High starting torque
B)Low cost
C)Better speed control
D)Wide speed range

168. Which of the following method of speed control, of D.C. machine will offer minimum efficiency?

A)Voltage control method
B)Armature control method
C)Field control method
D)All of these answers

169. Hopkinson’s test on D.C. machines is conducted at

A)overload
B)no-load
C)part load
D)full-load

170. Ward-Leonard system of speed control is not recommended for

A)constant speed operation
B)very low speeds
C)wide speed range
D)frequent motor reversals

171. If the field of a D.C. shunt motor gets opened while the motor is running

A)the speed of motor will be reduced
B)the motor will continue to run at constant speed
C)the armature current will reduce
D)the motor will attain dangerously high speed

172. What is the effect produced by the electric current in an electric motor?

A)Heating as well as chemical effect
B)Magnetic effect only
C)Heating effect only
D)Heating as well as magnetic effect

173. The current drawn by the armature of D.C. motor is directly proportional to

A)the voltage across the terminals
B)the speed of the motor
C)the torque required
D)none of these answers

174. Speed control by Ward Leonard method gives uniform speed variation

A)above normal speed only
B)in one direction
C)in both directions
D)below normal speed only

175. In D.C. motor which of the following can sustain the maximum temperature rise?

A)Commutator
B)Armature winding
C)Field winding
D)Slip rings

176. In which of the following applications D.C. series motor is invariably tried?

A)Starter for a car
B)Fan motor
C)Motor operation in A.C. or D.C.
D)Drive for a water pump

177. During rheostatic braking the braking torque is proportional to

A)​​(speed)-1
B)​​​​(speed)2
C)​​​​(speed)
D)​​​​(speed)-2

178. Small D.C. motors up to 5 H.P. usually have

A)2 poles
B)4 poles
C)8 poles
D)6 poles

179. D.C. series motors are used

A)where load changes frequently
B)none of these answers
C)where load is constant
D)where constant operating speed is needed

180. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?

A)Differentially compounded motor
B)Shunt motor
C)Cumulatively compounded motor
D)Series motor

181. Which losses can be determined by performing the retardation test?

A)Stray losses
B)Eddy current losses
C)Copper losses
D)Friction losses

182. For which types of D.C. motor, dynamic braking is generally used?

A)Compound motors
B)Shunt motors
C)All of these answers
D)Series motors

183. During rheostat braking of D.C. series motors

A)motor is reversed in direction
B)motor is run at reduced speed
C)motor is run as a generator
D)none of these answers

184. The speed of a series motor at no load is

A)2000 r.p.m.
B)infinity
C)1000 r.p.m.
D)4000 r.p.m.

185. A D.C. shunt motor is rotating in a clockwise direction as viewed from one end. The polarity of connection of the armature and field winding is reversed simultaneously. The motor will

A)will not rotate at all
B)gain excessively high speed
C)rotate in clockwise direction
D)rotate in anti-clockwise direction

186. As the load is increased the speed of the D.C. shunt motor will

A)increase slightly
B)increase proportionately
C)remains unchanged
D)reduce slightly

187. Four point starter in the D.C. motor is used

A)not to effect the current passing through Hold on coil even if any change M the field current takes place
B)to increase the field current
C)all of these answers
D)to decrease the field current

188. The series parallel system of speed control of D.C. series motors widely used in traction work gives a speed range of about

A)1 : 10
B)1 : 6
C)1 : 4
D)1 : 8

189. The starting resistance of a D.C. motor is generally

A)infinitely large
B)around 500 ohms
C)low
D)1000 ohms

190. For starting a D.C. motor a starter is required because

A)it limits the starting current to a safe value
B)it limits the speed of the motor
C)it starts the motor
D)none of these answers

191. Field winding of a D.C. series motor is usually provided with thick wire

A)as it carries large load current
B)to provide large flux
C)to reduce the use of insulating materials
D)in order to reduce eddy current

192. Which D.C. motor is generally preferred for cranes and hoists?

A)Shunt motor
B)Differentially compounded motor
C)Series motor
D)Cumulatively compounded motor

193. In D.C. machines fractional pitch winding is used

A)to increase the generated e.m.f.
B)to reduce copper losses
C)to improve cooling
D)to reduce the sparking

194. The retardation test is applicable to shunt motors and generators and is used to find

A)the eddy current losses
B)the copper losses
C)the friction losses
D)the stray losses

195. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor

A)is to be derated by a factor recommended by the manufacturer and select the next higher H.P. motor
B)of lower H.P. should be selected
C)can be used for 50°C ambient temperature also
D)of higher H.P. should be selected

196. Which of the following D.C. motors has the least drop in speed between no-load and nominal load?

A)Series motor with commutating poles
B)Compound motor without commutating poles
C)Series motor without commutating poles
D)Shunt motor with commutating pole

Click Here for Answers

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2 thoughts on “175+ DC Motors Objective Questions and Answers”

  1. TOOK THE WHOLE TEST WRITING DOWN MY ANSWERS ON A PAER
    I SCROLL DOWN WHERE IT SAYS “Click Here for Answers” IF I CLICK IT….
    IT MAKES ME ACTUALLY TAKE THE WHOLE QUIZ ALL OVER AGAIN.

    I SHOULD BE ABLE TO JUST CHECK MY ANSWERS WITH SOME SORT OF A “KEY”

    THIS IS SO STUPID

    Reply
    • You don’t need any separate key. Just use our online quiz. The answers are displayed immediately after completing each question. This way you can test your knowledge/skills.

      Reply

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