Chapter 7: Electrical Theory and DC Machines

Question 1

A2C07Q06 The symbol for flux density is _____ and the symbol for magnetic flux is ______.
Select one:

a.
μ, B

b.
ɸ, B

c.
ɸ, μ

d.
B, ɸ

Answer 1

d.
B, ɸ

Question 2

The yoke in a DC machine is usually made of:
Select one:

a.
Iron or steel

b.
Copper

c.
Aluminum

d.
Insulation

e.
Semi-conducting materials

Answer 2

a.
Iron or steel

Question 3

Interpoles are connected in series with the:
Select one:

a.
Field coils

b.
Load

c.
Armature

d.
Field poles

e.
Stator

Answer 3

c.
Armature

Question 4

The air gaps between the poles and the armature in a DC generator are:
Select one:

a.
Filled with insulation

b.
Subject to sparking

c.
Increased with speed

d.
Kept comparatively small

e.
To insulate the poles from the armature

Answer 4

d.
Kept comparatively small

Question 5

In a generator, the direction of the induced EMF can be determined by applying Fleming’s _____ hand rule.
Select one:

a.
Back

b.
Two

c.
Inverse

d.
Left

e.
Right

Answer 5

e.
Right

Question 6

The end shields of a DC generator hold the:
Select one:

a.
Armature conductors at the ends of the armature

b.
Field windings tightly to the field poles

c.
Brushes in contact with the armature

d.
Rotor and the armature together

e.
Bearing housings

Answer 6

e.
Bearing housings

Question 7

Excitation of the shunt field is controlled by a:
Select one:

a.
Regulating rheostat

b.
Mechanical governor

c.
Converter

d.
Long shunt

e.
Short shunt

Answer 7

a.
Regulating rheostat

Question 8

The armature core in a DC machine is made of:
Select one:

a.
Copper

b.
Copper laminations

c.
Hard steel laminations

d.
Soft iron laminations

e.
Stainless steel laminations

Answer 8

d.
Soft iron laminations

Question 9

The practical unit used to represent resistance is:
Select one:

a.
Impedance

b.
Amp

c.
Ohm

d.
Farad

e.
Henry

Answer 9

c.
Ohm

Question 10

A2C07Q05 Temporary magnets ______________.
Select one:

a.
Are easy to magnetize

b.
Are difficult to magnetize

c.
Have high retentivity

d.
Retain their magnetic characteristics easily

Answer 10

a.
Are easy to magnetize

Question 11

In a shunt motor, if the field becomes disconnected during operation, the motor will:
Select one:

a.
Overspeed

b.
Under speed

c.
Slow down

d.
Stop

e.
Not change

Answer 11

a.
Overspeed

Question 12

Factors that determine the resistance of a conductor are:
Select one:

a.
Weight, length, diameter, and temperature

b.
Type of material, length, diameter, and temperature

c.
Weight, type of material, length, and diameter

d.
Weight, type of material, length, diameter, and temperature

e.
Weight, length, temperature, and diameter

Answer 12

b.
Type of material, length, diameter, and temperature

Question 13

The assembled armature core of a DC machine:
Select one:

A.
Is wrapped with field windings

B.
Has axial slots around its periphery

C.
Contacts the brushes

D.
Is hard-drawn copper bars

E.
Is connected with the rotor

Answer 13

B.
Has axial slots around its periphery

Question 14

A2C07Q03 The strength of the magnetic field around a coil is determined by __________ and ______________.
Select one:

a.
The rate of change of current, its magnitude

b.
The magnitude of current, the number of turns

c.
The magnitude of current, its direction

d.
The direction of current, the number of turns

Answer 14

b.
The magnitude of current, the number of turns

Question 15

The behaviour of a separately excited generator with regard to its load characteristic is that as load increases, its delivery voltage:
Select one:

a.
Steeply rises

b.
Remains constant

c.
Slightly falls

d.
Slightly fluctuates

e.
Slightly above normal

Answer 15

c.
Slightly falls

Question 16

When a high starting torque is required, but the running load may be small, the best DC motor to use would be the _____ motor.
Select one:

a.
Series

b.
Shunt

c.
Compound

d.
Under compounded

e.
Over compounded

Answer 16

c.
Compound

Question 17

When a current carrying conductor is placed in a magnetic field, the field produced by the conductor _____ the magnetic field between the poles.
Select one:

a.
Adds to

b.
Subtracts from

c.
Distorts

d.
Crosses

e.
Straightens

Answer 17

c.
Distorts

Question 18

The separately excited DC generator has a _____ load characteristic:
Select one:

a.
Rising

b.
Level

c.
Falling

d.
Series

e.
Parallel

Answer 18

c.
Falling

Question 19

The valence (free) electrons of a conductor, when connected to the poles of a battery, move towards:
Select one:

a.
Both poles at the same time

b.
The negative pole

c.
The positive pole

d.
Either or both poles, quite randomly

e.
The cathode

Answer 19

c.
The positive pole

Question 20

As the flux of a shunt motor remains constant, its torque is:
Select one:

a.
Inversely proportional to armature current.

b.
Proportional to armature current.

c.
Increased.

d.
Decreased.

e.
Unchanged.

Answer 20

b.
Proportional to armature current.

Question 21

In a shunt motor, if the field becomes disconnected during operation, the motor will:
Select one:

a.
Overspeed

b.
Under speed

c.
Slow down

d.
Stop

e.
Not change

Answer 21

a.
Overspeed

Question 22

Factors that determine the resistance of a conductor are:
Select one:

a.
Weight, length, diameter, and temperature

b.
Type of material, length, diameter, and temperature

c.
Weight, type of material, length, and diameter

d.
Weight, type of material, length, diameter, and temperature

e.
Weight, length, temperature, and diameter

Answer 22

b.
Type of material, length, diameter, and temperature

Question 23

The assembled armature core of a DC machine:
Select one:

A.
Is wrapped with field windings

B.
Has axial slots around its periphery

C.
Contacts the brushes

D.
Is hard-drawn copper bars

E.
Is connected with the rotor

Answer 23

B.
Has axial slots around its periphery

Question 24

A2C07Q03 The strength of the magnetic field around a coil is determined by __________ and ______________.
Select one:

a.
The rate of change of current, its magnitude

b.
The magnitude of current, the number of turns

c.
The magnitude of current, its direction

d.
The direction of current, the number of turns

Answer 24

b.
The magnitude of current, the number of turns

Question 25

The behaviour of a separately excited generator with regard to its load characteristic is that as load increases, its delivery voltage:
Select one:

a.
Steeply rises

b.
Remains constant

c.
Slightly falls

d.
Slightly fluctuates

e.
Slightly above normal

Answer 25

c.
Slightly falls

Question 26

When a high starting torque is required, but the running load may be small, the best DC motor to use would be the _____ motor.
Select one:

a.
Series

b.
Shunt

c.
Compound

d.
Under compounded

e.
Over compounded

Answer 26

c.
Compound

Question 27

When a current carrying conductor is placed in a magnetic field, the field produced by the conductor _____ the magnetic field between the poles.
Select one:

a.
Adds to

b.
Subtracts from

c.
Distorts

d.
Crosses

e.
Straightens

Answer 27

c.
Distorts

Question 28

The separately excited DC generator has a _____ load characteristic:
Select one:

a.
Rising

b.
Level

c.
Falling

d.
Series

e.
Parallel

Answer 28

c.
Falling

Question 29

The valence (free) electrons of a conductor, when connected to the poles of a battery, move towards:
Select one:

a.
Both poles at the same time

b.
The negative pole

c.
The positive pole

d.
Either or both poles, quite randomly

e.
The cathode

Answer 29

c.
The positive pole

Question 30

As the flux of a shunt motor remains constant, its torque is:
Select one:

a.
Inversely proportional to armature current.

b.
Proportional to armature current.

c.
Increased.

d.
Decreased.

e.
Unchanged.

Answer 30

b.
Proportional to armature current.