Electrical Principles for the Electrical Trades Volume 1 Jim Jenneson 6th Edition- Test Bank
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Sample Test
Chapter 03
Student: ___________________________________________________________________________
1. Look
at the following diagram:
The above diagram shows the magnetic field produced by a bar
magnet. As they expand away from the magnet the magnetic fields:
1. become
weaker
1. gain
extra strength
1. begin
to alternate
1. change
polarity
2. By
convention a magnetic lines of force are considered to:
1. acts
outwards from the south-pole of a magnet and inwards at the north-pole
1. acts
outwards from the north-pole of a magnet and inwards at the south-pole
1. acts
outwards from the north-pole of a magnet and inwards at the north-pole
1. acts
outwards from the south-pole of a magnet and inwards at the south-pole
3. Magnetic
lines of force take the shortest possible path between the north and south
poles of a magnet. However, when a material that can be magnetised is placed
within the magnetic field, the field is distorted because a:
1. magnetic
material offers no opposition to the magnetic field
1. magnetic
material offers more opposition to the field than a non-magnetic material
1. magnetic
material offers less opposition to the field than a non-magnetic material
1. magnetic
line of force cannot pass through a magnetic material
4. Two
magnetic fields acting in the same direction will:
1. attract
one another
1. cancel
one another out
1. change
polarities with one another
1. repel
one another
5. For a
ferromagnetic material, the critical temperature above which the dipoles within
the material become easy to realign is called the:
1. Curie
point
1. Saturation
point
1. Magnetic
point
1. Ferro
point
6. When
a magnet is attracted to a piece of magnetic material, the magnetic field
passes through the material, turning it into a temporary magnet. This action is
called:
1. electromotive
induction
1. magnetic
induction
1. magnetic
polarisation
1. ferromagnetic
alignment
7. The
three most important magnetic materials are iron, nickel and:
1. copper
1. silver
1. cobalt
1. aluminium
8. One
alloy that has made into permanent magnets with superior properties; is Alnico.
This alloy consists mainly of:
1. silver,
nickel and cobalt
1. aluminium,
nickel and copper
1. aluminium,
nitrates and cobalt
1. aluminium,
nickel and cobalt
9. Ferromagnetic
materials which are easily magnetised are called:
1. magnetically
soft
1. magnetically
hard
1. mechanically
soft
1. physically
hard
10.
When the magnetising force is removed from a magnetically soft
material, the material tends to demagnetise itself. Any magnetism that remains
is called:
1. coercive
magnetism
1. residual
magnetism
1. electro-magnetism
1. permeability
magnetism
11.
Ferrite magnetic materials are manufactured:
1. from
ferromagnetic iron and steel products
1. at
very low temperatures using non-ferromagnetic materials
1. using
a mixture of powdered magnetic materials and a ceramic binder
1. by a
process of electroferro magnetisation
12.
Rare earth magnets make the strongest magnets currently
available. One common application of these magnets is:
1. the
magnetic field for rechargeable batteries
1. sintered
ferrite cores in electric motors
1. Curie
point temporary magnets for portable tools
1. electric
motor fields for permanent magnet motors
13.
When a device needs to be protected from a magnetic field, a
magnetic shield is used. Magnetic shields divert the magnetic field by:
1. providing
a path of much greater permeability
1. acting
as a magnetic insulator
1. blocking
the magnetic field in all directions
1. acting
as a very low permeability bypass
14.
Look at the following diagram:
The above drawing shows a magnetic chuck which uses the holding
power of magnets to retain magnetic materials firmly in position on the
worktable of a machine during machining processes. One important advantage of
the magnetic chuck is that:
1. the
event of an electrical failure, the material will be released
1. no
electrical connections are needed
1. magnetic
materials are free to move during the process
1. they
are much less expensive than four-jaw chucks
15.
When current travels along a conductor, a magnetic field
surrounds the conductor. This magnetic field:
1. increases
if the current decreases
1. decreases
if the current increases
1. increases
if the current increases
1. is
constant for values of current
16.
Electromagnets can replace permanent magnets in most
applications, with the added advantage that electromagnets:
1. are
made from rare-earth materials
1. do
not need to have a south pole
1. are
permanently in the magnetised state
1. can
be varied in magnetic strength
17.
The right-hand grip rule for straight conductors states that if
the imaginary conductor is gripped with the thumb pointing in the direction of
the current flow, then the fingers point in the direction of the:
1. magnetic
field
1. electron
flow
1. resistance
effect
1. supply
voltage
18.
Look at the following diagram:
Using the right-hand grip rule for a straight conductor, the
direction of the magnetic field in the above diagram will be:
1. clockwise
1. anti-clockwise
1. vertically
upwards
1. vertically
downwards
19.
Look at the following diagram:
With reference to the above diagram, the strength of the
magnetic field around a straight conductor depends on the value of the current
in the conductor. Doubling the current results in:
1. no
change to the strength of the magnetic field
1. a
change of direction in the magnetic field
1. double
the strength of the magnetic field
1. the
magnetic field beginning to alternate
20.
Look at the following diagram:
The above diagram illustrates the convention for indicating the
direction of current flow in a conductor. The ¤ symbol indicates the current is
flowing:
1. from
North to South
1. from
South to North
1. away
from the observer
1. towards
the observer
21.
By winding a conductor into a coil of many turns, the magnetic
field strength is:
1. increased
in proportion to the number of turns in the coil
1. decreased
in proportion to the number of turns in the coil
1. increased
in inverse proportion to the number of turns in the coil
1. increased
in proportion to magnetic field strength of the wire
22.
The direction of the magnetic field generated by a solenoid can
be determined using the right-hand grip rule. This rule states that when the
right hand is placed over a solenoid coil so that the fingers point in the
direction of the current flow, the thumb points in the direction of the:
1. South
pole of the magnetic field
1. North
pole of the of the magnetic field
1. current
through the solenoid
1. power
generated by the current flow
23.
Look at the following diagram:
The above diagram shows the magnetic forces between two
conductors carrying current in the same direction. This force causes the
conductors to:
1. rotate
clockwise
1. rotate
anticlockwise
1. be
attracted towards one another
1. be
repelled by one another
24.
Therefore, the magnetic force between two conductors with a
known current flow in each conductor and with a known distance separating the conductors
can be calculated from the formula:
1. F =
4E – 7 x I1I2 x s
1. F =
2E – 8 x I1I2/s
1. F =
2E – 7 x V1I1/s
1. F =
2E – 7 x I1I2/s
25.
Two long parallel conductors 0.015 m apart each carry a current
of 200 A in opposite directions. The force between them will be:
1. 0.53
Newtons
1. 0.053
Newtons
1. 0.026
Newtons
2. 2.60
Newtons
26.
The force required to create a magnetic field is called the:
1. electromotive
force
1. magnetomotive
force
1. electrostatic
force
1. magnodynamic
forcer
27.
The magnetic field strength of a coil is proportional to the
product of the:
1. north
and south poles of the coil
1. current
and the length of the coil
1. current
and the number of turns in the coil
1. supply
voltage and the number of turns in the coil
28.
The following formula can be used to determine the magnetomotive
force in a magnetic circuit:
Fm = IN
In the formula the symbol ‘N’ stands for the:
1. current
flowing in amperes
1. number
of magnetic poles in the circuit
1. magnetising
node strength number
1. number
of turns in coil
29.
A current of 7 A flows in a coil of 100 turns, the value of MMF
creating a magnetic flux is:
1. 700
At
1. 170
At
1. 107
At
14.
14.28 At
30.
The magnetising force for a portion of a magnetic circuit is the
MMF required to magnetise a unit length of a magnetic path and is expressed in:
1. ampere-turns
per Henry
1. ampere-turns
per metre
1. amperes
per applied volts
1. Webers
per metre
31.
The flux density of a magnetic circuit is measured in:
1. volts
per metre
1. ampere
turns per volt
1. webers
per square metre
1. teslas
per square metre
32.
The flux density of a magnetic path can be found from the
formula:
In the formula the symbol Φ stands for:
1. cross-sectional
area of the magnetic circuit
1. change
in current in amperes
1. flux
density in teslas per square metre
1. total
magnetic flux in webers
33.
A magnetic circuit has a cross-sectional area of 100 mm2 and a
flux density of 0.015T. The total flux in the circuit will be:
1. 1.5
E-6 Wb
2. 2.5
E-6 Wb
1. 0.15
E-6 Wb
1. 100
E-6 Wb
34.
A conductor carrying a current within a magnetic field will
have:
1. no
opposition to current flow
1. a
force placed upon it
1. no
magnetic field around it
1. one
induced tesla per metre
35.
The value of the force on a conductor within a magnetic flux can
be found from the formula,
In the formula, the symbol B stands for:
1. current
in amperes
1. length
of the conductor in metre
1. flux
density in teslas
1. flux
density in webers
36.
A conductor has been placed at right angles to a magnetic field
with a flux density of 0.5 T over a length of 0.15 m of the conductor. If the
current through the conductor is 15 A, then force exerted on the conductor will
be:
15.
15.65 N
11.
11.25 N
1. 1.565
N
1. 1.125
N
37.
The permeability of a magnetic material is defined as the:
1. ease
with which a magnetic flux can be created in that material
1. opposition
to a magnetic flux being created in that material
1. amount
of permanent magnetism left when the current stops
1. ability
of a magnetic material to become a permanent magnet
38.
The permeability of free space (a vacuum), is equal to:
1. 2πE –
7
1. 4πE –
7
1. 4πE –
8
1. 2πE –
8
39.
To find the actual permeability of a material, the following
formula can be used:
In the formula, the symbol μr is used for the:
1. actual
permeability of the material
1. permeability
of the material in a vacuum
1. relative
permeability of the material
1. permeability
of free space
40.
The term used to describe the opposition by a material to being
magnetised is:
1. magnetic
permeability
1. magnetic
acceptance
1. magnetomotive
flux ratio
1. magnetic
reluctance
41.
The reluctance of a magnetic circuit depends on a number of
factors. These are the length, the cross sectional area and the:
1. permeability
of the circuit material
1. distance
around the circuit material
1. electrical
current through the circuit material
1. number
of North and South poles in the magnetic circuit
42.
The reluctance of a magnetic circuit can be found using the
formula shown below.
In the formula the symbol ‘A’ stands for the:
1. current
in amperes in the electrical circuit
1. cross-sectional
area of the magnetic circuit
1. absolute
value of the magnetic permeability
1. length
of the magnetic circuit in metres
43.
An iron core has a total mean length of magnetic path of 250 mm.
The core is rectangular in cross-section with dimensions 15 mm x 15 mm. The
core has a relative permeability of 800 at the designed flux density. The reluctance
of the core will be:
1. 1.105
E4 AT/Wb
1. 1.268
E6 AT/Wb
1. 1.105
E6 AT/Wb
884.
884.1 E6 AT/Wb
44.
The equivalent of Ohm’s Law for magnetic circuits is stated as:
In the formula the term IN represents the:
1. magnetic
flux in the magnetic circuit in webers
1. reluctance
of the circuit in ampere turns per weber
1. electromotive
force in amperes2 per tesla
1. magnetomotive
force in ampere-turns
45.
An electromagnet has 500 turns and the total reluctance of the
magnetic core is 750 IN/Wb. The flux produced when 12 A flows through the coil
will be:
1. 8 Wb
12.
12.8 Wb
1. 6000
Wb
1. 9000
Wb
46.
A contactor coil has 7000 turns and draws 0.12 A from the
supply. When energised the total flux produced by the coil is 700 E-6 Wb. The
magnetic reluctance of this circuit is:
7. 7.2
E-6 AT/Wb
1. 1.2
E-6 AT/Wb
1. 72
E-6 AT/Wb
1. 12
E-6 AT/Wb
47.
With reference to the magnetising characteristic of non-magnetic
materials, the flux density ‘B’ varies directly with magnetising force ‘H’. Therefore
the graph of ‘B’ against ‘H’ will be:
1. in
the shape of a parabola
1. exponential
1. a
straight line
1. in
the shape of a peak
48.
B/H curves are commonly used as a means of comparing the:
1. voltage
of a battery against a magnetic circuit
1. magnetising
force against the relative permeability of a magnetic material
1. ampere
turns of a magnetic circuit against the magnetising force
1. magnetic
characteristics of different types of magnetic materials
49.
Look at the following graph:
The B/H curve in the diagram above shows that when the value of
H is low, small increases in the value of the magnetising force (H) will
produce:
1. large
increases in the value of the flux density
1. small
increases in the value of the flux density
1. no increases
in the value of the flux density
1. saturated
increases in the value of the flux density
50.
With reference to the drawing shown above in QUESTION 49, as the
magnetising force increases towards 2000 AT/m, the flux density increases less
and less. This indicates that magnetic saturation is taking place. Saturation
is said to occur at a flux density near the:
1. bottom
of the B/H curve
1. centre
of the knee of the B/H curve
1. middle
of the vertical section of the B/H curve
1. ankle
of the B/H curve
51.
Look at the following graph:
The graph illustrates the magnetisation curves for silicon
steel, cast steel and cast iron. The curves show that silicon steel saturates
at a:
1. slightly
higher value of flux density than cast steel
1. slightly
lower value of flux density than cast iron
1. slightly
lower value of flux density than cast steel
1. much
lower value of flux density than cast steel
52.
The graph in QUESTION 51 illustrates the magnetisation curves
for silicon steel, cast steel and cast iron. The curves show that cast iron is:
1. much
easier to magnetise than silicon steel
1. much
easier to magnetise than cast steel
1. much
harder to magnetise than cast iron
1. much
harder to magnetise than silicon steel
53.
In electrical terminology term ‘hysteresis’ is used to describe
the lag between a change in value or direction of the magnetising force and
the:
1. resulting
change in value or direction of flux
1. resulting
change in the value of the magnetising force
1. change
in the value of coercive force required
1. change
in the value of residual force required for flux
54.
Even after the magnetising force is removed, some magnetism
remains. This is known as:
1. hysteresis
magnetic flux
1. residual
magnetism
1. latent
magnetising force
1. coercive
flux
55.
The force that is used to remove residual magnetism is known as
the:
1. residual
force
1. magnetising
force
1. coercive
force
1. hysteresis
force
56.
Look at the following graph:
The graph represents the hysteresis loop of the magnetising
force plotted against the flux density in both directions. On the graph, OB and
OE indicate the values of:
1. magnetising
force at maximum flux density
1. flux
density at minimum magnetising force
1. residual
magnetising force at zero flux density
1. residual
flux density at zero magnetising force
57.
Reversing the magnetic field within the magnetic material
results in the:
1. generation
of heat within the material
1. flux
density increasing
1. the material
reversing its direction
1. temperature
of the material lowering
58.
Look at the following graph:
The graph compares the hysteresis loops of transformer steel and
carbon steel. The hysteresis loop with the comparatively small area:
1. has
greater losses than the other
1. is
for transformer steel
1. indicates
that carbon steel has less hysteresis losses
1. requires
a greater magnetising force
59.
Look at the following diagram:
With reference to the magnetic circuit shown above, the total magnetic
flux does not reach the air gap, but leaves the iron poles and passes through
the surrounding air. The flux which leaves the main path is known as:
1. the
magnetomotive force
1. negative
magnetic flux
1. the
leakage flux
1. magnetising
coil flux
60.
Look at the following diagram:
The above drawing shows a simple attracted-armature type of
relay. When current flows in the operating coil, a magnetic flux is created:
1. between
the moving contacts of the external circuit
1. in
the fixed contact of the external circuit
1. only
in the air gap only between the armature and core
1. in
the soft iron core and around the magnetic circuit
61.
Some electrical machines are prone to failure when the supply
voltage is lower than the value that the machine was designed for. No-volt
relays, low-volt relays or brown-out relays, have an operating coil connected
across the supply voltage. In these relays, the armature and contacts close
when the:
1. supply
is energised
1. supply
is de-energised
1. supply
voltage is very low
1. supply
is DC only
62.
The operating coil of an overload relay is connected:
1. in
parallel with the current flowing in the circuit
1. in
series with the current flowing in the circuit
1. so
that the supply voltage appears across the coil
1. so
that it reads the minimum current flow in the circuit
63.
Polarised relays operate only when:
1. an AC
supply is applied
1. the
relay is connected to an alternating supply
1. the
polarity of a DC supply is correct
1. the
magnetic circuit has two North di-poles
Chapter 03 Key
1. Look
at the following diagram:
The above diagram shows the magnetic field produced by a bar
magnet. As they expand away from the magnet the magnetic fields:
1. become
weaker
1. gain
extra strength
1. begin
to alternate
1. change
polarity
Chapter 3.3—EKAS 2.8.6: A1
EPC 8, 9, 40
Jenneson – Chapter 03 #1
KS01-EG101A T1
2. By
convention a magnetic lines of force are considered to:
1. acts
outwards from the south-pole of a magnet and inwards at the north-pole
1. acts
outwards from the north-pole of a magnet and inwards at the south-pole
1. acts
outwards from the north-pole of a magnet and inwards at the north-pole
1. acts
outwards from the south-pole of a magnet and inwards at the south-pole
Chapter 3.3—EKAS 2.8.6:A1, A2 & A3
EPC 8, 9, 40
Jenneson – Chapter 03 #2
KS01-EG101A T1
3. Magnetic
lines of force take the shortest possible path between the north and south
poles of a magnet. However, when a material that can be magnetised is placed
within the magnetic field, the field is distorted because a:
1. magnetic
material offers no opposition to the magnetic field
1. magnetic
material offers more opposition to the field than a non-magnetic material
1. magnetic
material offers less opposition to the field than a non-magnetic material
1. magnetic
line of force cannot pass through a magnetic material
Chapter 3.3—EKAS 2.8.6: A1, A2 & A3
EPC 8, 9, 40
Jenneson – Chapter 03 #3
KS01-EG101A T1
4. Two
magnetic fields acting in the same direction will:
1. attract
one another
1. cancel
one another out
1. change
polarities with one another
1. repel
one another
Chapter 3.3.1.—EKAS 2.8.6: A1, A2 & A3
EPC 8, 9, 40
Jenneson – Chapter 03 #4
KS01-EG101A T1
5. For a
ferromagnetic material, the critical temperature above which the dipoles within
the material become easy to realign is called the:
1. Curie
point
1. Saturation
point
1. Magnetic
point
1. Ferro
point
Chapter 3.3.1.—EKAS 2.8.6: A1, A2 & A3
EPC 8, 9, 40
Jenneson – Chapter 03 #5
KS01-EG101A T1
6. When
a magnet is attracted to a piece of magnetic material, the magnetic field
passes through the material, turning it into a temporary magnet. This action is
called:
1. electromotive
induction
1. magnetic
induction
1. magnetic
polarisation
1. ferromagnetic
alignment
Chapter 3.3.2—EKAS 2.8.6—A1, A2 & A3
EPC 8, 9, 40
Jenneson – Chapter 03 #6
KS01-EG101A T1
7. The
three most important magnetic materials are iron, nickel and:
1. copper
1. silver
1. cobalt
1. aluminium
Chapter 3.3.3—EKAS 2.8.6: A1, A2, A3 & A4
EPC 8, 9, 40
Jenneson – Chapter 03 #7
KS01-EG101A T1
8. One
alloy that has made into permanent magnets with superior properties; is Alnico.
This alloy consists mainly of:
1. silver,
nickel and cobalt
1. aluminium,
nickel and copper
1. aluminium,
nitrates and cobalt
1. aluminium,
nickel and cobalt
Chapter 3.3.3—EKAS 2.8.6: A1, A2, A3 & A4
EPC 8, 9, 40
Jenneson – Chapter 03 #8
KS01-EG101A T1
9. Ferromagnetic
materials which are easily magnetised are called:
1. magnetically
soft
1. magnetically
hard
1. mechanically
soft
1. physically
hard
Chapter 3.3.3—EKAS 2.8.6: A1, A2, A3 & A4
EPC 8, 9, 40
Jenneson – Chapter 03 #9
KS01-EG101A T1
10.
When the magnetising force is removed from a magnetically soft
material, the material tends to demagnetise itself. Any magnetism that remains
is called:
1. coercive
magnetism
1. residual
magnetism
1. electro-magnetism
1. permeability
magnetism
Chapter 3.3.3—EKAS 2.8.6: A1, A2, A3 & A4
EPC 8, 9, 40
Jenneson – Chapter 03 #10
KS01-EG101A T1
11.
Ferrite magnetic materials are manufactured:
1. from
ferromagnetic iron and steel products
1. at
very low temperatures using non-ferromagnetic materials
1. using
a mixture of powdered magnetic materials and a ceramic binder
1. by a
process of electroferro magnetisation
Chapter 3.3.3—EKAS 2.8.6: A1, A2, A3 & A4
EPC 8, 9, 40
Jenneson – Chapter 03 #11
KS01-EG101A T1
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