DC Machines: Master the Fundamentals for Electrical Engineers

Question 1

The torque generated by a DC motor is directly proportional to:

Accepted Answer

Product of armature and field currents.

Answer

Armature current only.

Answer

Field current only.

Answer

Supply voltage.

Question 2

A DC generator primarily functions to convert:

Accepted Answer

Mechanical energy into electrical energy.

Answer

Electrical energy into mechanical energy.

Answer

Chemical energy into electrical energy.

Answer

Thermal energy into electrical energy.

Question 3

Armature reaction in a DC machine results in:

Accepted Answer

An opposing magnetic field to the field winding.

Answer

An assisting magnetic field to the field winding.

Answer

No impact on the magnetic field.

Answer

Increased power output.

Question 4

Which application is generally not suited for DC machines?

Accepted Answer

High-fidelity audio systems.

Answer

Electric vehicles.

Answer

Industrial drives.

Answer

Renewable energy generation.

Question 5

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

Accepted Answer

Synchronous

Answer

Series

Answer

Shunt

Answer

Compound

Question 6

Which type of DC machine is commonly used for traction applications, such as electric locomotives?

Accepted Answer

Series

Answer

Shunt

Answer

Compound

Answer

Permanent magnet

Question 7

What is the effect of armature reaction in a DC machine?

Accepted Answer

It creates a cross-magnetizing effect

Answer

It causes the magnetic field to weaken

Answer

It increases the machine's efficiency

Answer

It has no significant impact

Question 8

What is a characteristic of a saturated magnetic circuit in a DC machine?

Accepted Answer

Nonlinear variation of flux

Answer

Constant inductance

Answer

High permeability

Answer

Low reluctance

Question 9

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

Accepted Answer

To conduct current to produce torque

Answer

To create the rotating magnetic field

Answer

To generate the magnetic flux

Answer

To provide mechanical support to the rotor

Question 10

Which type of DC machine maintains a nearly constant speed regardless of load?

Accepted Answer

Shunt motor

Answer

Series motor

Answer

Compound motor

Answer

Permanent magnet motor

Question 11

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

Accepted Answer

To create a stationary magnetic field

Answer

To regulate the speed

Answer

To generate voltage

Answer

To store electrical energy

Question 12

What is the fundamental principle governing the generation of torque in a DC machine?

Accepted Answer

Fleming's right-hand rule

Answer

Faraday's law of induction

Answer

Lenz's law

Answer

Gauss's law

Question 13

Which test is commonly used to assess the condition of a DC machine's insulation?

Accepted Answer

Megger test

Answer

High-potential test

Answer

Continuity test

Answer

Resistance test

Question 14

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

Accepted Answer

AC Machine

Answer

Compound Motor

Answer

Shunt Motor

Answer

Series Motor

Question 15

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

Accepted Answer

To reverse the direction of current flow in the armature conductors, ensuring continuous rotation.

Answer

To store energy and regulate voltage

Answer

To provide mechanical support to the armature

Answer

To reduce sparking and improve commutation

Question 16

What is the significance of back-EMF in a DC motor?

Accepted Answer

It opposes the applied voltage, regulating the motor's speed and limiting its maximum speed.

Answer

It reduces the current consumption of the motor, improving efficiency.

Answer

It has no significant impact on the operation of the DC motor.

Answer

It increases the torque produced by the motor, enhancing its power output.

Question 17

What is the purpose of a field weakening resistor in a DC motor?

Accepted Answer

To reduce the field current, which increases the motor's speed beyond its base speed.

Answer

To increase the field current, which reduces the motor's speed below its base speed.

Answer

To improve the motor's efficiency by reducing power losses.

Answer

To protect the motor from overloads by limiting the current flow.

Question 18

What is the fundamental principle behind the operation of DC generators?

Accepted Answer

Faraday's law of electromagnetic induction, which describes the generation of electromotive force (EMF) due to a changing magnetic field.

Answer

Kirchhoff's law, which describes the conservation of energy and charge in electrical circuits.

Answer

Lenz's law, which determines the direction of induced EMF based on the direction of magnetic field change.

Answer

Ohm's law, which relates voltage, current, and resistance in electrical circuits.