DC Motor Questions and Answers pdf [MCQs]: We will discuss the chapter DC Motors Questions with Answers from the subject Electricity Engineering.
DC Motor Questions and Answers pdf
1. Which of the following is NOT a type of DC motor?
a) Shunt-wound
b) Compound-wound
c) Series-wound
d) All of the above are types of DC motors
Answer: d) All of the above are types of DC motors
2. In a DC motor, the armature winding is located on the:
a) Rotor
b) Stator
c) Both rotor and stator
d) None of the above
Answer: a) Rotor
3. The function of the commutator in a DC motor is to:
a) Control the speed of the motor
b) Reverse the direction of the motor
c) Convert AC voltage to DC voltage
d) Switch the current direction in the armature winding
Answer: d) Switch the current direction in the armature winding
4. A shunt-wound DC motor has:
a) High starting torque and low speed regulation
b) Low starting torque and high speed regulation
c) High starting torque and high speed regulation
d) Low starting torque and low speed regulation
Answer: c) High starting torque and high speed regulation
5. Which of the following is NOT a disadvantage of a DC motor?
a) Requires periodic maintenance
b) Limited speed range
c) High cost
d) Generates electromagnetic interference (EMI)
Answer: c) High cost
6. The speed of a DC motor is controlled by varying the:
a) Voltage applied to the armature
b) Voltage applied to the field winding
c) Resistance of the armature winding
d) Resistance of the field winding
Answer: a) Voltage applied to the armature
7. The back EMF in a DC motor is proportional to the:
a) Armature current
b) Field current
c) Armature voltage
d) Field voltage
Answer: a) Armature current
8. The torque produced by a DC motor is proportional to the:
a) Armature current
b) Field current
c) Armature voltage
d) Field voltage
Answer: a) Armature current
9. A compound-wound DC motor has:
a) High starting torque and high speed regulation
b) Low starting torque and high speed regulation
c) High starting torque and low speed regulation
d) Low starting torque and low speed regulation
Answer: a) High starting torque and high speed regulation
10. Which of the following is a disadvantage of a series-wound DC motor?
a) Limited speed range
b) Low starting torque
c) High cost
d) Generates electromagnetic interference (EMI)
Answer: a) Limited speed range
11. The efficiency of a DC motor is highest at:
a) Low load and high speed
b) High load and low speed
c) High load and high speed
d) Low load and low speed
Answer: b) High load and low speed
12. The armature reaction in a DC motor results in:
a) Increased efficiency
b) Reduced speed regulation
c) Reduced torque
d) Distortion of the magnetic field
Answer: d) Distortion of the magnetic field
13. A DC motor with a separately excited field winding has:
a) A fixed magnetic field
b) A variable magnetic field
c) No magnetic field
d) None of the above
Answer: b) A variable magnetic field
14. The no-load speed of a DC motor is:
a) The maximum speed the motor can achieve
b) The speed at which the motor produces maximum torque
c) The speed of the motor when there is no load on the shaft
d) None of the above
Answer: c) The speed of the motor when there is no load on the shaft
15. The armature resistance in a DC motor affects:
a) Starting torque
b) Speed regulation
c) Efficiency
d) All of the above
Answer: d) All of the above
16. The torque-speed characteristics of a DC motor are typically represented on a:
a) Torque-speed curve
b) Voltage-current curve
c) Resistance-capacitance curve
d) None of the above
Answer: a) Torque-speed curve
17. In a DC motor, the torque produced is proportional to the:
a) Armature voltage
b) Field voltage
c) Armature current
d) Field current
Answer: c) Armature current
18. The efficiency of a DC motor is calculated as:
a) Output power / Input power
b) Input power / Output power
c) Armature current x Field current
d) Armature voltage x Field voltage
Answer: a) Output power / Input power
19. The function of the brushes in a DC motor is to:
a) Control the speed of the motor
b) Reverse the direction of the motor
c) Provide electrical contact between the rotating armature and stationary circuit
d) Switch the current direction in the armature winding
Answer: c) Provide electrical contact between the rotating armature and stationary circuit
20. A DC motor can be used as a:
a) Generator
b) Transformer
c) Capacitor
d) None of the above
Answer: a) Generator
21. The term “armature reaction” in a DC motor refers to the:
a) Movement of the armature winding
b) Interaction between the armature and field windings
c) Voltage applied to the armature winding
d) None of the above
Answer: b) Interaction between the armature and field windings
22. The term “commutation” in a DC motor refers to the:
a) The process of reversing the direction of the motor
b) The process of switching the current direction in the armature winding
c) The process of changing the speed of the motor
d) None of the above
Answer: b) The process of switching the current direction in the armature winding
23. The speed of a DC motor can be controlled by:
a) Changing the voltage applied to the field winding
b) Changing the resistance of the armature winding
c) Changing the voltage applied to the armature winding
d) All of the above
Answer: c) Changing the voltage applied to the armature winding
24. In a DC motor, the direction of rotation can be reversed by:
a) Reversing the voltage applied to the field winding
b) Reversing the voltage applied to the armature winding
c) Reversing the current flow in the field winding
d) Reversing the current flow in the armature winding
Answer: b) Reversing the voltage applied to the armature winding
25. A DC motor operates on which principle?
a) Electromagnetic induction
b) Electromagnetic force
c) Electromagnetic radiation
d) None of the above
Answer: b) Electromagnetic force
26. A DC shunt motor is connected to a supply voltage of 220V. The armature resistance is 0.5 ohms and the field resistance is 220 ohms. Calculate the armature current when the motor is delivering a torque of 20 Nm.
a) 90 A
b) 100 A
c) 110 A
d) 120 A
Answer: a) 90 A
27. Which type of DC motor is most suitable for applications where high starting torque is required?
a) Series motor
b) Shunt motor
c) Compound motor
d) Synchronous motor
Answer: a) Series motor
28. The speed of a DC motor can be increased by:
a) Increasing the armature voltage
b) Decreasing the armature voltage
c) Increasing the field current
d) Decreasing the field current
Answer: a) Increasing the armature voltage
29. In a DC motor, if the back EMF is greater than the supply voltage, the motor will:
a) Stop rotating
b) Continue to rotate at a constant speed
c) Increase in speed
d) Decrease in speed
Answer: c) Increase in speed
30. Which of the following statements about a DC motor is true?
a) The direction of rotation can be changed by changing the direction of the current in the field winding
b) The direction of rotation can be changed by changing the direction of the current in the armature winding
c) The direction of rotation is determined by the design of the motor and cannot be changed
d) None of the above
Answer: b) The direction of rotation can be changed by changing the direction of the current in the armature winding
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31. The armature winding of a DC motor is connected to a commutator, which consists of:
a) A ring of insulating material
b) A ring of conducting material
c) A series of brushes
d) A and C
Answer: b) A ring of conducting material
32. The torque produced by a DC motor is directly proportional to the:
a) Field current
b) Armature voltage
c) Armature current
d) Field voltage
Answer: c) Armature current
33. Which type of DC motor is most suitable for applications where constant speed is required?
a) Series motor
b) Shunt motor
c) Compound motor
d) Synchronous motor
Answer: b) Shunt motor
34. The efficiency of a DC motor is typically in the range of:
a) 30-50%
b) 50-70%
c) 70-90%
d) 90-100%
Answer: c)
35. What is the function of a commutator in a DC motor?
a) To connect the armature to the power supply
b) To reverse the direction of the magnetic field
c) To convert AC power to DC power
d) To change the direction of the current in the armature winding
Answer: d) To change the direction of the current in the armature winding
36. The direction of rotation of a DC motor is determined by:
a) The direction of the current in the field winding
b) The direction of the current in the armature winding
c) The design of the motor
d) None of the above
Answer: b) The direction of the current in the armature winding
37. In a DC motor, the back EMF is:
a) The voltage generated in the field winding
b) The voltage generated in the armature winding
c) The voltage supplied to the motor
d) None of the above
Answer: b) The voltage generated in the armature winding
38. Which of the following is not a type of DC motor?
a) Series motor
b) Shunt motor
c) Compound motor
d) Synchronous motor
Answer: d) Synchronous motor
39. Which of the following statements about a DC shunt motor is true?
a) It has a high starting torque
b) Its speed is proportional to the armature voltage
c) It is suitable for applications where constant speed is required
d) It is not affected by changes in load
Answer: b) Its speed is proportional to the armature voltage
40. The speed of a DC motor is inversely proportional to:
a) The armature current
b) The field current
c) The armature voltage
d) The field voltage
Answer: a) The armature current
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41. The efficiency of a DC motor is defined as:
a) The ratio of the output power to the input power
b) The ratio of the input power to the output power
c) The ratio of the mechanical power to the electrical power
d) The ratio of the electrical power to the mechanical power
Answer: a) The ratio of the output power to the input power
42. A DC motor has a rated voltage of 24 V and a rated current of 2 A. What is the rated power of the motor?
a) 24 W
b) 48 W
c) 72 W
d) 96 W
Answer: b) 48 W
43. In a DC series motor, the torque-speed characteristics are:
a) Almost constant at all loads
b) High at low speeds and low at high speeds
c) Low at low speeds and high at high speeds
d) Independent of the load
Answer: b) High at low speeds and low at high speeds
44. The speed regulation of a DC motor is defined as:
a) The percentage change in speed from no load to full load
b) The percentage change in torque from no load to full load
c) The percentage change in armature current from no load to full load
d) The percentage change in armature voltage from no load to full load
Answer: a) The percentage change in speed from no load to full load
45. Which of the following factors can cause a DC motor to overheat?
a) Excessive load
b) Low voltage
c) High speed
d) All of the above
Answer: d) All of the above
46. A DC shunt motor is running at its rated speed with no load. What happens to the speed if the field current is increased?
a) The speed decreases
b) The speed increases
c) The speed remains the same
d) The motor stalls
Answer: c) The speed remains the same
47. A DC motor is driving a load that requires a constant torque. Which type of DC motor is suitable for this application?
a) Series motor
b) Shunt motor
c) Compound motor
d) None of the above
Answer: b) Shunt motor
48. The armature resistance of a DC motor is 0.5 Ω and the armature current is 10 A. What is the voltage drop across the armature?
a) 2.5 V
b) 5 V
c) 10 V
d) 20 V
Answer: b) 5 V
49. A DC motor is drawing 5 A from a 12 V supply. What is the power consumption of the motor?
a) 17 W
b) 30 W
c) 60 W
d) 120 W
Answer: b) 60 W
50. Which of the following is an advantage of a DC motor over an AC motor?
a) DC motors are more efficient
b) DC motors have a wider speed range
c) DC motors are easier to control
d) All of the above
Answer: d) All of the above
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51. What is the main disadvantage of a series DC motor?
a) It has low starting torque
b) It is difficult to control the speed
c) It has a tendency to become unstable at high speeds
d) It has low efficiency at high speeds
Answer: c) It has a tendency to become unstable at high speeds
52. What is the function of the field winding in a DC motor?
a) To generate the magnetic field
b) To convert electrical energy to mechanical energy
c) To regulate the speed of the motor
d) To protect the motor from overload
Answer: a) To generate the magnetic field
53. Which of the following is a disadvantage of a DC shunt motor?
a) It has a low starting torque
b) Its speed is not constant under varying loads
c) It is difficult to control the speed
d) It is expensive
Answer: b) Its speed is not constant under varying loads
54. Which of the following statements about a DC compound motor is true?
a) Its speed is proportional to the armature voltage
b) Its speed is proportional to the field current
c) It has a high starting torque
d) It is suitable for applications where constant speed is required
Answer: b) Its speed is proportional to the field current
55. What is the function of the brushes in a DC motor?
a) To connect the armature to the power supply
b) To convert AC power to DC power
c) To provide a sliding contact between the armature and the commutator
d) To regulate the speed of the motor
Answer: c) To provide a sliding contact between the armature and the commutator
56. What is the effect of increasing the voltage applied to a DC motor?
a) The speed of the motor increases
b) The torque of the motor increases
c) The power consumption of the motor increases
d) All of the above
Answer: d) All of the above
57. What is the purpose of the armature core in a DC motor?
a) To generate the magnetic field
b) To provide mechanical support for the armature winding
c) To convert electrical energy to mechanical energy
d) None of the above
Answer: b) To provide mechanical support for the armature winding
58. Which of the following is a characteristic of a DC motor?
a) It can operate on AC power
b) Its speed is not affected by the load
c) Its speed is proportional to the armature current
d) It has a constant torque at all speeds
Answer: c) Its speed is proportional to the armature current
59. A DC motor has a rated speed of 1000 rpm and a rated torque of 5 Nm. What is the rated power of the motor?
a) 500 W
b) 1000 W
c) 2500 W
d) 5000 W
Answer: b) 1000 W
60. What is the function of the armature winding in a DC motor?
a) To generate the magnetic field
b) To convert electrical energy to mechanical energy
c) To regulate the speed of the motor
d) To protect the motor from overload
Answer: b) To convert electrical energy to mechanical energy
61. Which of the following types of DC motor is used in applications where a high starting torque is required?
a) DC series motor
b) DC shunt motor
c) DC compound motor
d) All of the above
Answer: a) DC series motor
62. What is the advantage of a DC shunt motor?
a) It has a high starting torque
b) Its speed is proportional to the armature current
c) Its speed is constant under varying loads
d) It is cheaper than other types of DC motors
Answer: c) Its speed is constant under varying loads
63. Which of the following types of DC motor is used in applications where a constant speed is required?
a) DC series motor
b) DC shunt motor
c) DC compound motor
d) None of the above
Answer: b) DC shunt motor
64. Which of the following is a characteristic of a DC motor that makes it suitable for use in electric vehicles?
a) High starting torque
b) High efficiency at high speeds
c) Ability to operate on both AC and DC power
d) All of the above
Answer: a) High starting torque
65. Which of the following factors determines the speed of a DC motor?
a) The strength of the magnetic field
b) The number of poles
c) The armature voltage
d) All of the above
Answer: d) All of the above
66. Which of the following types of DC motor is used in applications where both high starting torque and constant speed are required?
a) DC series motor
b) DC shunt motor
c) DC compound motor
d) None of the above
Answer: c) DC compound motor
67. Which of the following statements about a DC motor is true?
a) It requires a special type of power supply to operate
b) It has a fixed speed under varying loads
c) It can be used in both motor and generator applications
d) It is more efficient than an AC motor
Answer: c) It can be used in both motor and generator applications
68. What is the function of the commutator in a DC motor?
a) To provide a sliding contact between the armature and the brushes
b) To convert AC power to DC power
c) To regulate the speed of the motor
d) To generate the magnetic field
Answer: a) To provide a sliding contact between the armature and the brushes
69. Which of the following factors determines the torque of a DC motor?
a) The strength of the magnetic field
b) The number of poles
c) The armature current
d) All of the above
Answer: d) All of the above
70. Which of the following types of DC motor is used in applications where high torque and variable speed are required?
a) DC series motor
b) DC shunt motor
c) DC compound motor
d) None of the above
Answer: a) DC series motor