Question 1

Which component in a DC machine is responsible for collecting the current generated in the armature conductors?

Accepted Answer

Commutator

Question 2

In a DC machine, what is the primary material used for brushes, and why is it chosen?

Accepted Answer

Carbon or graphite, because they provide good electrical contact and wear resistance

Question 3

What is the main function of the commutator in a DC motor?

Accepted Answer

To provide current to the armature conductors

Question 4

If a DC machine has 24 armature coils, how many commutator segments should it have?

Accepted Answer

$24$

Question 5

Which winding method is NOT typically used for armature windings in DC machines?

Accepted Answer

Random winding

Question 6

Why are armature conductors insulated from each other and from the armature core?

Accepted Answer

To prevent short circuits and ensure proper current flow

Question 7

What is the purpose of providing air ducts for axial air flow in the armature core?

Accepted Answer

To cool the armature and reduce current losses

Question 8

In the construction of an A.C. induction motor, what is the stator core typically made of?

Accepted Answer

Thin metal sheets called laminations

Question 9

Which of the following statements about the commutator is TRUE?

Accepted Answer

It consists of copper segments insulated from each other

Question 10

A DC generator is running and the commutator is not making proper contact with the brushes. What is the most likely consequence?

Accepted Answer

The output current will be unstable or interrupted

Question 11

Which part of a DC machine is keyed to the shaft and rotates with it?

Accepted Answer

Armature

Question 12

In a practical scenario, why might an engineer choose wave winding over lap winding for a DC machine?

Accepted Answer

Wave winding is preferred for high voltage, low current applications

Question 13

Which of the following is a critical reason for using laminations in the stator core of an AC induction motor?

Accepted Answer

To reduce eddy current losses

Question 14

If the armature winding in a DC machine is not properly insulated, which of the following is most likely to occur?

Accepted Answer

Short circuits between conductors

Question 15

In a DC machine, what is the relationship between the number of commutator segments ($N_c$) and the number of armature coils ($N_a$)?

Accepted Answer

$N_c = N_a$

Question 16

Which of the following best describes the role of brushes in a DC machine?

Accepted Answer

They collect or supply current by maintaining physical contact with the commutator segments

Question 17

A DC motor is used in a medical device requiring precise speed control. Which component is most critical for ensuring smooth current supply to the armature?

Accepted Answer

Brushes

Question 18

In the context of reducing current losses in the armature core, which engineering solution is most effective?

Accepted Answer

Providing air ducts for axial air flow

Question 19

Which of the following is NOT a function of the commutator in a DC machine?

Accepted Answer

Insulating the armature from the shaft

Question 20

A factory is experiencing frequent failures in their DC motors due to excessive brush wear. Which material change could most likely improve brush life?

Accepted Answer

Switching to graphite brushes

Fundamentals of DC and AC Machine Construction (Not Statistics)

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