Chapter 7: Electrical Theory and DC Machines Flashcards
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
d.
B, ɸ
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
a.
Iron or steel
Interpoles are connected in series with the:
Select one:
a.
Field coils
b.
Load
c.
Armature
d.
Field poles
e.
Stator
c.
Armature
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
d.
Kept comparatively small
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
e.
Right
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
e.
Bearing housings
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
a.
Regulating rheostat
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
d.
Soft iron laminations
The practical unit used to represent resistance is:
Select one:
a.
Impedance
b.
Amp
c.
Ohm
d.
Farad
e.
Henry
c.
Ohm
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
a.
Are easy to magnetize
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
a.
Overspeed
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
b.
Type of material, length, diameter, and temperature
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
B.
Has axial slots around its periphery
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
b.
The magnitude of current, the number of turns
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
c.
Slightly falls
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
c.
Compound
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
c.
Distorts
The separately excited DC generator has a _____ load characteristic:
Select one:
a.
Rising
b.
Level
c.
Falling
d.
Series
e.
Parallel
c.
Falling
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
c.
The positive pole
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.
b.
Proportional to armature current.
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
a.
Overspeed
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
b.
Type of material, length, diameter, and temperature
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
B.
Has axial slots around its periphery
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
b.
The magnitude of current, the number of turns
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
c.
Slightly falls
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
c.
Compound
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
c.
Distorts
The separately excited DC generator has a _____ load characteristic:
Select one:
a.
Rising
b.
Level
c.
Falling
d.
Series
e.
Parallel
c.
Falling
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
c.
The positive pole
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.
b.
Proportional to armature current.
