# DC Motor Questions and Answers pdf [MCQs]

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

#### 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)

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

8. The torque produced by a DC motor is proportional to the:

a) Armature current

b) Field current

c) Armature voltage

d) Field voltage

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)

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

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

17. In a DC motor, the torque produced is proportional to the:

a) Armature voltage

b) Field voltage

c) Armature current

d) Field 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

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

d) None of the above

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

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

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

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

## DC Motor MCQ | DC Machines Questions and Answers pdf

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

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

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%

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

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

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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

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

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

45. Which of the following factors can cause a DC motor to overheat?

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

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

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

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

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

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

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

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

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

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

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