DC Machines: Construction, Operation, and Characteristics

Question 1

Which of these is NOT a type of DC machine?

Accepted Answer

Induction motor

Answer

Shunt motor

Answer

Series motor

Answer

Permanent magnet motor

Question 2

Which of the following is NOT a type of DC machine?

Accepted Answer

Induction motor

Answer

Series motor

Answer

Shunt motor

Answer

Permanent magnet motor

Question 3

What types of DC machines are there?

Accepted Answer

DC generator and DC motor

Answer

AC generator

Answer

DC transformer

Answer

DC tachogenerator

Question 4

What is the function of the armature in a DC machine?

Accepted Answer

To conduct current and generate EMF when it rotates in a magnetic field

Answer

To rotate the shaft

Answer

To generate a magnetic field

Answer

To provide mechanical support

Question 5

What is the purpose of interpoles in a DC machine?

Accepted Answer

To reduce armature reaction and improve commutation

Answer

To increase efficiency

Answer

To generate magnetic field

Answer

To control speed

Question 6

What is the key difference between a cumulative compound DC motor and a differential compound DC motor?

Accepted Answer

The direction in which the series field windings are connected

Answer

The speed-torque characteristics

Answer

The type of armature winding

Answer

The number of poles

Question 7

What is the primary purpose of a starter in a DC motor?

Accepted Answer

To limit the starting current and protect the motor from damage

Answer

To reverse the direction of rotation

Answer

To control the speed

Answer

To increase the starting torque

Question 8

The commutator in a DC machine serves to:

Accepted Answer

Reverse the direction of current flow in the armature

Answer

Step up the voltage in the armature

Answer

Interrupt the armature current

Answer

Control the speed of the machine

Question 9

The field winding in a DC generator is responsible for:

Accepted Answer

Producing the magnetic field in the stator

Answer

Controlling the speed of rotation

Answer

Carrying the armature current

Answer

Regulating the output voltage

Question 10

A shunt generator is characterized by:

Accepted Answer

Maintaining a relatively constant output voltage under varying load conditions

Answer

Providing a constant output current

Answer

Operating at a fixed speed

Answer

Producing a variable output voltage

Question 11

The fundamental difference between a DC motor and a DC generator is that:

Accepted Answer

A DC motor converts electrical energy into mechanical energy, while a DC generator converts mechanical energy into electrical energy

Answer

DC motors operate at a fixed speed, while DC generators operate at a variable speed

Answer

DC motors have a commutator, while DC generators do not

Answer

DC motors are used for high-power applications, while DC generators are used for low-power applications

Question 12

The primary purpose of a starter in a DC motor is to:

Accepted Answer

Limit the high starting current and protect the motor from damage

Answer

Control the speed of the motor

Answer

Reverse the direction of rotation

Answer

Increase the starting torque

Question 13

A major advantage of using a compound generator is:

Accepted Answer

Improved voltage regulation under varying load conditions

Answer

Simplified maintenance

Answer

Increased efficiency

Answer

Reduced production cost

Question 14

Which component is NOT typically found in a DC motor?

Accepted Answer

Capacitor

Answer

Armature

Answer

Commutator

Answer

Field windings

Question 15

What is the primary purpose of the commutator in a DC motor?

Accepted Answer

To reverse the direction of current flow in the armature windings

Answer

To connect the armature windings to the external circuit

Answer

To store electrical energy

Question 16

Which factor does NOT influence the speed of a DC motor?

Accepted Answer

Load torque

Answer

Armature current

Answer

Field current

Answer

Supply voltage

Question 17

How does the field current typically affect the torque produced by a DC motor?

Accepted Answer

The torque is directly proportional to the field current

Answer

The torque is inversely proportional to the field current

Answer

The torque is not affected by the field current

Question 18

What is the primary purpose of a DC series motor?

Accepted Answer

To provide high starting torque

Answer

To ensure a constant speed

Answer

To achieve high efficiency

Answer

To operate quietly

Question 19

Which type of DC generator utilizes permanent magnets to produce a magnetic field?

Accepted Answer

Permanent magnet generator

Answer

AC generator

Answer

Induction generator

Answer

Synchronous generator

Question 20

What is the main function of the armature windings in a DC generator?

Accepted Answer

To generate electromotive force (EMF)

Answer

To minimize sparking

Answer

To store electrical energy

Answer

To connect the generator to an external circuit

Question 21

Which factor does NOT affect the output voltage of a DC generator?

Accepted Answer

Load current

Answer

Strength of the magnetic field

Answer

Speed of rotation

Answer

Number of armature conductors

Question 22

How does the speed of a DC generator typically relate to its output voltage?

Accepted Answer

Output voltage is directly proportional to speed

Answer

Output voltage is not affected by speed

Answer

Output voltage is inversely proportional to speed

Question 23

What is the primary function of a DC motor?

Accepted Answer

To convert electrical energy into mechanical energy

Answer

To amplify electrical signals

Answer

To store electrical energy

Answer

To regulate voltage in a circuit

Question 24

Which factor primarily determines the direction of rotation of a DC motor?

Accepted Answer

Polarity of the applied voltage across the armature

Answer

Strength of the magnetic field generated by the field windings

Answer

Speed of rotation of the armature

Answer

Direction of the current flow in the armature

Question 25

Which of the following is a type of DC generator?

Accepted Answer

Shunt generator

Answer

AC generator

Answer

Induction generator

Answer

Three-phase generator

Question 26

What is the function of the commutator in a DC machine?

Accepted Answer

To reverse the direction of current flow in the armature windings

Answer

To reduce the speed of rotation

Answer

To increase the voltage output

Question 27

How are series-wound and shunt-wound DC motors different?

Accepted Answer

Series-wound motors have higher starting torque but poorer speed regulation than shunt-wound motors.

Answer

Both series-wound and shunt-wound motors have the same starting torque and speed regulation.

Answer

Shunt-wound motors have higher starting torque but poorer speed regulation than series-wound motors.

Question 28

What is the relationship between the back EMF of a DC motor and its speed?

Accepted Answer

Back EMF increases as the speed of the motor increases.

Answer

Back EMF is not related to the speed of the motor.

Answer

Back EMF decreases as the speed of the motor increases.

Answer

Back EMF remains constant regardless of the speed of the motor.

Question 29

How is the efficiency of a DC generator defined?

Accepted Answer

The ratio of the output power to the input power

Answer

The ratio of the armature current to the field current

Answer

The ratio of the back EMF to the applied voltage

Answer

The ratio of the input power to the output power

Question 30

Which characteristic distinguishes a DC compound generator?

Accepted Answer

It can operate as both a shunt and a series generator.

Answer

It has only a shunt field winding.

Answer

It has only a series field winding.

Answer

It produces a constant voltage regardless of load.

Question 31

Which of the following is NOT a type of DC machine?

Accepted Answer

AC motor

Answer

DC generator

Answer

DC motor

Question 32

What is the purpose of the field winding in a DC generator?

Accepted Answer

To generate a magnetic field

Answer

To convert mechanical energy to electrical energy

Answer

To regulate the voltage output

Answer

To reverse the direction of current flow

Question 33

What is the fundamental difference between a DC motor and a DC generator?

Accepted Answer

The direction of energy conversion

Answer

Construction

Answer

Cost

Answer

Size

Question 34

What is the significance of the back electromotive force (EMF) in a DC motor?

Accepted Answer

It limits the motor's speed

Answer

It increases the torque

Answer

It controls the armature current

Answer

It reverses the direction of rotation

Question 35

Which of the following is NOT a type of DC motor?

Accepted Answer

Induction motor

Answer

Series motor

Answer

Shunt motor

Question 36

What is the primary function of the commutator in a DC machine?

Accepted Answer

To convert the alternating current produced in the armature winding to direct current

Answer

To control the speed of the machine

Answer

To increase the voltage output of the machine

Question 37

Why is a starter used in a DC motor circuit?

Accepted Answer

To limit the starting current and protect the motor from damage

Answer

To reverse the direction of rotation

Answer

To increase the voltage applied to the motor

Question 38

What is the main difference between a DC series motor and a DC shunt motor?

Accepted Answer

A series motor has a higher starting torque but lower speed regulation, while a shunt motor has a lower starting torque but better speed regulation.

Answer

A series motor has higher speed regulation, while a shunt motor has lower speed regulation

Answer

A series motor has higher efficiency, while a shunt motor has lower starting torque

Question 39

What is the primary function of a field rheostat in a DC motor circuit?

Accepted Answer

To adjust the motor speed by changing the field current

Answer

To reverse the direction of rotation

Answer

To limit the current during starting

Question 40

What is a characteristic of a DC shunt generator?

Accepted Answer

It produces a relatively constant voltage output.

Answer

It has a variable voltage output.

Answer

It has a variable current output.

Answer

It produces a constant current output.

Question 41

What is the main advantage of a DC compound generator compared to a DC shunt generator?

Accepted Answer

It provides better voltage regulation, especially under load.

Answer

It has higher efficiency.

Answer

It is smaller in size.

Answer

It is less expensive.

Question 42

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

Accepted Answer

To convert alternating current induced in the armature winding to direct current.

Answer

To increase the speed of the motor.

Answer

To reduce voltage in the armature circuit.

Answer

To provide a path for field current.

Question 43

Which DC motor type is commonly employed in applications that demand high starting torque, such as cranes or elevators?

Accepted Answer

Series wound motor

Answer

Permanent magnet motor

Answer

Separately excited motor

Answer

Shunt wound motor

Question 44

In a DC generator, the field current directly influences the generated voltage. How does increasing the field current affect the generated voltage?

Accepted Answer

Increases

Answer

Remains constant

Answer

Fluctuates randomly

Answer

Decreases

Question 45

What is the essential purpose of the armature winding in a DC generator?

Accepted Answer

To generate electromotive force (EMF) when rotated within a magnetic field.

Answer

To act as a conductor for field current.

Answer

To control the generator's speed.

Question 46

In a DC motor operating at a constant speed, how does an increase in the load affect the armature current?

Accepted Answer

Increases

Answer

Remains constant

Answer

Decreases

Answer

Varies unpredictably

Question 47

Which of the following is not a typical application for DC motors?

Accepted Answer

Large-scale power generation plants

Answer

Electric vehicles

Answer

Industrial machinery

Question 48

What is the primary advantage of utilizing a shunt wound DC motor over a series wound DC motor?

Accepted Answer

Superior speed regulation

Answer

Lower production cost

Answer

Simplified construction

Answer

Increased starting torque

Question 49

In a DC generator operating at a constant speed, how does an increase in the load affect the armature current?

Accepted Answer

Increases

Answer

Remains constant

Answer

Decreases

Answer

Fluctuates randomly

Question 50

Define back EMF in a DC motor.

Accepted Answer

An electromotive force generated in the armature winding due to its rotation in a magnetic field, opposing the applied voltage.

Answer

The voltage drop across the armature resistance

Question 51

In a DC motor connected to a variable voltage supply, how does a decrease in voltage affect the motor's speed?

Accepted Answer

Decreases

Answer

Remains constant

Answer

Fluctuates unpredictably

Answer

Increases