magnetic circuit parameters
Magnetic flux (
)
where:
– magnetic flux (Maxwell)
In cgs units:
– reluctance (Gilbert/Henry)
magnetic circuit units
Weber – SI unit of magnetic flux
equal to 108 lines or maxwells.
Named after the German
physicist Wilhelm Weber (18041891)
Maxwell – cgs unit of magnetic
flux equal to one line of force.
Named after the Scottish
physicist, James Clerk Maxwell
(1831-1879)
magnetic circuit units
Gilbert – cgs unit of
magnetomotive force. Named
after the English physician and
physicist, William Gilbert (15401603)
where:
– mmf (Gilbert)
N – number of turns
I – electrical current flowing
(ampere)
magnetic circuit units
Tesla – SI unit of magnetic flux
density equal to Webers per
square meter. Named after the
Crotian-American engineer
Nikola Tesla (1856-1943)
Gauss – cgs unit of magnetic flux
density equal to Maxwells per
square centimeter. Name after
the German mathematician
Johann Karl Freidrich Gauss
(1777-1855)
magnetic circuit units
Oersted – cgs unit of magnetic
field strength equal to Gilbert per
centimeter. Named after the
Danish physicist and chemist
Hans Christian Oersted (17771851)
magnetic field strength (H)
The mmf per unit length of path
of the magnetic flux.
where:
– magnetic field strength
(ampere-turn per meter)
– mean length of flux lines
(meter)
– magnetomotive force
(ampere-turn)
magnetic field strength (H)
Reluctance – the opposition
offered in a magnetic circuit to
the flow of magnetic flux
Permeance – the reciprocal of
reluctance
magnetic field strength (H)
Permeability – the ability of a
material to allow magnetic flux to
flow
Reluctivity – reciprocal of
permeability
reluctance in series
reluctance in parallel
energy stored in a magnetic circuit
where:
Wm – energy stored (joule)
µ - permeability of core
electric and magnetic circuits
Electric circuit
Magnetic circuit
Symbol
Unit
Quantity
V or E
Volt
I
R
J
G
Symbol
Unit
Quantity
Emf
Amp-turn
Mmf
Amp
Current
Weber
Magnetic flux
Ohm
Resistance
1/H
Reluctance
V/m
Field strength
H
Amp/m
Magnetization
A/m
Current density
B
Tesla
Flux density
Ω-m
Resistivity
m/H
Reluctivity
Siemens
Conductance
Henry
Permeance
S/m
Conductivity
H/m
Permeability
P
magnetic units conversion
Quantity
SI
CGS
Magnetomotive
force
Ampere-turn
(A-t)
Gilbert
(Gb)
Magnetic field
strength H
Ampere-meter
(A/m)
Oersted
(Oe;
Gb/cm)
Magnetic flux
Weber (Wb)
Maxwell
(Mx)
Magnetic flux
density B
Tesla (T;
Wb/m2)
Gauss (G;
Mx/cm2)
Relation
electromagnetic induction
Faraday’s law
The magnitude of the
electromotive force (emf) induced
in a circuit is proportional to the
rate of change of the magnetic
flux that cuts across the circuit.
Faraday’s first law of electromagnetic induction
Electromotive force is induced
whenever a conductor cuts
magnetic flux.
Faraday’s second law of electromagnetic
induction
The magnitude of the induced
emf is proportional to the relative
rate of change of flux.
Mathematically,
where:
– induced emf (volt)
– number of turns of the
conductor
– rate of change of flux (Wb/sec)
Lenz’s law
In electromagnetic induction, the
current set up by an induced
voltage tends to create flux
whose direction opposes any
change in the existing flux.
induced emf in a short length of wire
Based from the first law, a
voltage can be induced in a
conductor if moved across a
magnetic field so that flux cutting
results. This is also known as
Faraday’s principle.
where:
– induced emf (volt)
– flux density at the location of
the conductor (Tesla)
– length of the conductor (meter)
– relative velocity (meter per
second)
– flux cut by the conductor
(Weber)
– time of flux cutting (second)
The existence of a magnetic
field can always be traced
to:
a. a source of voltage
b. the geometric field
c. the solar magnetic field
d. the motion of electrically
charged particles
A permanent magnet:
a. needs no power source
b. works only off of dc
c. works only off of ac
d. can work of either dc or
ac
The atomic number of an
element is:
a. the number of ions in the
nucleus
b. the number of electrons
orbiting the nucleus
c. the number of charged
carriers
d. the number of protons in
the nucleus
Elements can join together
to form:
a. ions
b. isotopes
c. nuclei
d. compounds
If you placed a bar of ion
inside a cylindrical coil of
wire, and then run dc
through the wire, you have:
a. a rheostat
b. a permanent magnet
c. a flux meter
d. an electromagnet
The geomagnetic field is
distorted by
a. radio signals
b. the gravitational of the
moon
c. the magnetic field of the
moon
d. the solar winds
The tiniest element of
matter is the
a. atom
b. proton
c. electron
d. neutron
All matter, weather a gas, a
solid or a liquid is composed
of
a. atoms
b. protons
c. electrons
d. neutrons
Known as the simplest type
of atom to exist
a. hydrogen
b. oxygen
c. helium
d. boron
Revolve about the positive
nucleus in a definite orbit
a. electron
b. neutron
c. proton
d. atom
Diameter of hydrogen atom
a. 1.1 x 10-8 cm
b. 1.1 x 10-8 mn
c. 1.1 x 10-8 nm
d. 1.1 x 10-8 pm
Uncharged particles that
have no effect upon the
atomic charge
a. neutron
b. proton
c. nucleon
d. electron
Find the velocity that an
electron must attain in order
to be emitted from a
tungsten material if Ø=4.53
volts (work function for
Tungsten). m=9.1 x 1031 kg
and e=1x10-19
a. 1.26 m/sec
b. 1.26 mm/sec
c. 0.126 km/sec
d. 12.26 km/sec
The point in a magnet
where the intensity of
magnetic lines of force is
maximum
a. magnetic pole
b. south pole
c. north pole
d. great circle
The name given to
nonmetallic materials that
have the ferromagnetic
properties of iron
a. ferrites
b. ferromagnetic
c. diamagnetic
d. paramagnetic
The point at which a
magnetic material losses its
ferromagnetic properties is
called
a. Curie temperature
b. inferred absolute
temperature
c. room temperature
d. absolute temperature
A commercially alloy of
aluminum, nickel, and iron
with cobalt, copper and
titanium added to produced
about 12 grades
a. brass
b. alnico
c. manganin
d. constantan
The air space between
poles of a magnet is called
a. air gap
b. free space
c. atmosphere
d. vacuum
The idea preventing one
component from affecting
another through their
common electric or
magnetic field is called
a. shielding
b. Hall effect
c. grounding
d. limiting
An effect which is generally
used in the gauss meter to
measure flux density
a. skin effect
b. Hall effect
c. piezoelectric effect
d. magnetic effect
How much is the flux in
Webers?
a. 5 x 10-5
b. 5 x 105
c. 5 x 103
d. 5 x 10-3
Calculate the flux density in
tesla for a 200µWb flux
through an area of 5 x 10-4
sq. m.
a. 0.4
b. 0.3
c. 0.2
d. 0.1
The magnetic flux of 2000
lines is how many
maxwells?
a. 2000
b. 3000
c. 1000
d. 4000
The CGS unit of
magnetomotive force (mmf)
is:
a. Maxwell
b. Ampere-turn
c. Gilbert
d. Weber
One ampere-turn equals
a. 1.26 Gilberts
b. 1.36 Gilberts
c. 1.46 Gilberts
d. 1.56 Gilberts
An alloy consisting of 40
percent iron and 60 percent
nickel
a. hipernik
b. manganin
c. permalloy
d. alnico
A collapsing field around a
coil
a. tends to oppose the
decay of coil current
b. helps the decay of coil
current
c. tends to aid current flow
reversal
d. does not affect the coil
current flow
The coefficient of coupling
between two-air core coil
depends on
a. self inductance of the
two coils and their
mutual inductance
b. self inductance of the
two coils only
c. mutual inductance of the
coils only
d. the flux produced by one
of them
Whenever a conductor cuts
magnetic flux, an emf is
induced. This statement is
known as the
a. Ohm’s law
b. Joule’s law
c. Faraday’s law
d. Coulomb’s law
Magnetic lines of force is
called
a. current
b. hysteresis
c. flux
d. magnetomotive force
A solenoid 25 cm long is
wound with 200 turns, what
is the value of the field
strength inside the solenoid,
when the carrying a current
of 2 amperes
a. 1600 At/m
b. 1400 At/m
c. 1200 At/m
d. 1000 At/m
The force between two
magnetic varies with
distance between the
variation is
a. in inversely proportional
to the square of the
distance
b. in direct proportional to
the square of the
distance
c. in inversely proportional
to the distance
d. in direct proportional to
the distance
According to the Lenz’s law
the direction of the induced
emf and hence current
a. always opposes the
cause producing it
b. maybe found by the left
hand rule
c. maybe found by the right
hand rule
d. is determined by the rate
of cutting flux
Discovered the relationship
between magnetism and
electricity that serves as the
foundation for the theory of
electromagnetism
a. Hans Christian Oersted
b. Luigi Galvani
c. Andre Ampere
d. Charles Coulomb
Demonstrated that forced
between charges is
inversely related to the
square of the distance
between them in 1784
a. Andre Ampere
b. Charles Coulomb
c. Luigi Galvani
d. William Gilbert
Demonstrated in 1831 the
theory of electromagnetic
induction
a. James Clerk Maxwell
b. Andre Ampere
c. Charles Coulomb
d. Michael Faraday
One electron volt (1ev) is
equivalent to
a. 1.6 x 10-19 J
b. 1.5 x 10-19 J
c. 1.4 x 10-19 J
d. 1.3 x 10-19 J
The permissible number of
orbiting electrons in the first
shell or K shell is
a. 3
b. 1
c. 2
d. 4
A material such as
Germanium has exactly ___
valence electron(s)
a. 8
b. 2
c. 4
d. 1
Germanium atom has 32
protons and ___ electron(s)
a. 32
b. 41
c. 30
d. 28
Copper atom has how many
neutrons?
a. 32
b. 29
c. 33
d. 32
A unit of magnetic flux
density is:
a. ampere
b. tesla
c. volt per ampere
d. ampere per volt
An electrically charged atom
is:
a. an ion
b. an isotope
c. a conductor
d. a charge carrier
Alnico is:
a. the trade name for
manufacturer of toroid
cores
b. a type of wire used in
making electromagnets
c. a solenoid coil
d. an alloy used in making
permanent magnets
In a toroidal coil, the
magnetic flux line are:
a. perpendicular to the
plane containing the
toroid
b. circles within the toroid
c. radiating outward in all
directions
d. straight lines within the
toroid
Two atoms having the same
number of protons, but
different numbers of
neutron, represent different
a. elements
b. ions
c. isotopes
d. charge Carriers
If on looking at any one end
of a solenoid, the direction
of current flow is found to
the clockwise then the end
under observation is a
south-pole is called
a. end rule
b. cork screw rule
c. right hand rule
d. left hand rule
If the solenoid is gripped by
the right hand with the
fingers pointing the direction
of current flow the
outstretched thumb will then
point to the north-pole is
known as:
a. helix rule
b. end rule
c. cork screw rule
d. left hand rule
If a right handed bottleopener cork screw is
assumed to be along the
conductor so as to advance
in the direction of current
flow, the motion of its handle
will indicate the direction of
magnetic flux produced
around the conductor is
known as:
a. right hand rule
b. left hand rule
c. cork screw rule
d. end rule
The property of magnetic
materials of retaining
magnetism after the
withdrawal of magnetizing
force is referred to as:
a. retentivity
b. reluctivity
c. resistivity
d. conductivity
The quantity of magnetism
retained by magnetic
material after withdrawal of
the magnetizing force is
called:
a. residual magnetism
b. leftover
c. hysteresis
d. coercivity
The amount of magnetizing
force to counter balance the
residual magnetism of a
magnetic material is
referred to as:
a. coercivity
b. retentivity
c. susceptibility
d. reluctivity
The straight line passing
through the two poles of a
magnet is called
a. magnetic axis
b. Cartesian axis
c. real axis
d. imaginary axis
A group of magnetically
aligned atoms
a. domain
b. range
c. lattice
d. crystal
The lagging effect between
the flux density of the
material and the
magnetizing force applied is
called:
a. hysteresis
b. eddy currents
c. reluctance
d. permeance
A law establishing the fact
that the algebraic sum of the
rises and drops of the mmf
around a close loop of a
magnetic circuit is Equal to
zero
a. Ampere’s circuital law
b. Kirchoff’s circuital law
c. Maxwell’s circuital law
d. Coulomb’s circuital law
The unit of electromotive
force
a. voltage (V)
b. ampere-turns (At)
c. tesla (T)
d. Gilberts (Gb)
The relative permeability of
paramagnetic substance is:
a. slightly greater than 1
b. equal to 1
c. slightly less than 1
d. very much greater than 1
The magnetic materials can
be easily magnetized in
both directions are known
as:
a. soft magnetic materials
b. hard magnetic materials
c. high hysteresis loss
materials
d. low hysteresis loss
materials
Materials that have
permeabilities slightly less
than that of free space are:
a. nonmagnetic
b. paramagnetic
c. ferromagnetic
d. diamagnetic
Materials whose
permeabilities are slightly
greater than that of free
space are called:
a. ferromagnetic
b. paramagnetic
c. diamagnetic
d. non-magnetic
Materials that have very
high permeabilities (hundred
and even thousands of
times that of free space) are
called:
a. paramagnetic
b. ferromagnetic
c. diamagnetic
d. non-magnetic
The unit of reluctance is:
a. At/Wb
b. Maxwell
c. Gauss
d. Weber
A natural magnet is called:
a. steel
b. lodestone
c. magnesia
d. soft iron
Permeance is analogous to:
a. conductance
b. reluctance
c. resistance
d. admittance
The magnetic potential in a
magnetic circuit can be
measured in terms of:
a. mmf
b. emf
c. farad
d. coulomb
108 maxwells is equivalent
to:
a. 1 Weber
b. 1 Tesla
c. 1 Gauss
d. 1 Gilbert
Defined as the number of
lines per unit area through
any substance in a plane at
right angles to the lines of
force.
a. flux intensity
b. flux density
c. flux lines
d. flux
The ability of a material to
conduct magnetic flux
through it is called:
a. permittivity
b. reluctivity
c. permeability
d. conductivity
The ratio of the permeability
of material to the
permeability of air of
vacuum is called:
a. relative conductivity
b. relative permittivity
c. relative permeability
d. relative reluctivity
The force acting of a unit npole placed at that point is
called:
a. electric field intensity
b. magnetic field intensity
c. intensity of
magnetization
d. electromagnetic field
intensity
Defined as the flux density
produced in it due to its own
induced magnetism
a. electric field intensity
b. magnetic field intensity
c. intensity magnetization
d. electromagnetic field
intensity
The force of attraction or
repulsion between two poles
is inversely proportional to
the square of the distance
between them is:
a. Newton’s first law
b. Newton’s second law
c. Coulomb’s first law
d. Coulomb’s second law
May be defined as that pole
which when places in a air
from a similar and equal
pole repels it with a force of
1/4 π μ (base) o Newtons
a. magnet pole
b. unit pole
c. North pole
d. South pole
The phenomenon by which
a magnetic substance
becomes magnet when it is
placed near a magnet is
called:
a. magnetic induction
b. electromagnetic
induction
c. magnetic phenomenon
d. magnetic effect
The space outside the
magnet where its pole have
a force of attraction or
repulsion on a magnetic
pole is called:
a. electric field
b. magnetic field
c. electromagnetic field
d. free space field
The total number of
magnetic lines of force in a
magnetic field is called
a. magnetic potential
b. magnetic flux intensity
c. magnetic flux density
d. magnetic flux
In SI system, the unit of
magnetic flux is
a. Weber
b. Tesla
c. Maxwell
d. Gauss
Flux linkage equals
a. flux x number of turns
b. flux x area of core
c. flux x number of turns x
area of core
d. flux x number of turns x
length of core
When a conductor is
stationary and the magnetic
field is moving or charging,
the emf induced is called:
a. dynamically induced emf
b. statistically induced emf
c. self induced emf
d. mutually induced emf
The emf induced in a coil
due to the change of its own
flux linked with it is called:
a. statistically induced emf
b. mutually induced emf
c. dynamically induced emf
d. self induced emf
A coil has an inductance of
___ henry(ies) if an emf of 1
volt is induced in it when the
current is changing at the
rate of 1 ampere per second
a. 1
b. 2
c. 3
d. 4
The emf induced in a coil
due to the changing current
of another neighboring coil
is called:
a. dynamically induced emf
b. statistically induced emf
c. mutually induced emf
d. self induced emf
May be defined as a closed
path in which magnetic
induction or flux flows
a. magnetic circuit
b. electric circuit
c. electromagnetic circuit
d. electronic circuit
The force which setups or
tends to set up magnetic
flux in a magnetic circuit
a. dynamic force
b. potential difference
c. electromotive force
d. magnetomotive force
The name given to that
property of a material which
opposes the creation of
magnetic flux in it
a. resistance
b. reluctance
c. permeance
d. conductance
It is the reciprocal of
reluctance and implies the
case or readiness with
which magnetic flux is
developed
a. permeance
b. resistance
c. reluctance
d. conductance
It is the specific reluctance
of a material
a. permeability
b. conductivity
c. resistivity
d. reluctivity
The flux that does not follow
the intended path in a
magnetic circuit is called:
a. linked flux
b. lost flux
c. leakage flux
d. leakage current
The ratio of the total flux
(flux in iron path) to the
useful flux (flux in air gap) is
called:
a. leakage factor
b. leakage coefficient
c. leakage constant
d. leakage flux
Comparing electric and
magnetic circuits, the
current of electric circuit is
analogous to which
parameter of magnetic
circuit?
a. mmf
b. flux
c. flux density
d. reluctivity
Which of the following is a
vector quantity?
a. relative permeability
b. magnetic field intensity
c. magnetic potential
d. flux density
It is difficult to magnetize
steel because of its:
a. low permeability
b. high permeability
c. high retentivity
d. high density
A substance that attracts
pieces of iron
a. semiconductor
b. superconductor
c. magnet
d. conductor
The phenomenon by which
a substance attracts pieces
of iron is called:
a. magnetism
b. electromagnetism
c. naturalism
d. materialism
The force of attraction or
repulsion between two
magnetic poles directly
proportional to their
strengths is called:
a. Newton’s first law
b. Newton’s second law
c. Coulomb’s first law
d. Coulomb’s second law
The process by which an
emf and hence current is
generated or induced in a
conductor when there is a
change in the magnetic flux
linking the conductor is
called:
a. electromagnetic
interference
b. electromagnetic
induction
c. mutual induction
d. Faraday’s law
Whenever the flux linking a
coil or current changes, an
emf is induced in it is known
as:
a. Faraday’s first law of
electromagnetic
induction
b. Faraday’s second law of
electromagnetic
induction
c. Coulomb’s law
d. Joule’s law
The magnitude of induced
emf in a coil is directly
proportional to the rate of
change flux linkages is
known as:
a. Faraday’s first law of
electromagnetic
induction
b. Faraday’s second law of
electromagnetic
induction
c. Coulomb’s law
d. Joule’s law
A substance in which
electrons easily move is:
a. an ion
b. an isotope
c. a conductor
d. a nonconductor
When the orientation of the
electric flux rotates
uniformly as a signal travels
through space, that signal
is:
a. circularly polarized
b. randomly polarized
c. unpolarized
d. irregularly polarized
What law in electronics
where an induced current
will be in such a direction
that its own magnetic field
will oppose the magnetic
fields that produce the
same?
a. electromagnetic law
b. Norton’s law
c. Lenz’s law
d. Maxwell’s law
______________ has a unit
of electron volt (eV)
a. charge
b. potential difference
c. energy
d. current
What elements possess four
valence electrons?
a. insulators
b. semi-insulators
c. semiconductors
d. conductors
The difference in energy
between the valence and
conductor bands of a
semiconductor is called
a. band gap
b. extrinsic photo effect
c. conductivity
d. energy density
When an atom gains an
additional ______________,
it results to a negative ion
a. neutron
b. proton
c. electron
d. atom
What term in electronics is
used to express how fast
energy is consumed?
a. load
b. power
c. conductance
d. volt
Current carried by each of
two long parallel conductors
is doubled, if their
separation is also doubled,
the force between them
would
a. increase by four-fold
b. become half
c. increase two-fold
d. remain the same
A good material conductor
should have ________
valence electrons
a. 21
b. 1
c. 3.5
d. 10
The term used to express
the amount of electrical
energy in an electrostatic
field
a. coulombs
b. watts
c. volts
d. joules
The loss of electrical energy
in counter balancing the
residual magnetism in each
cycle is called
a. eddy current loss
b. hysteresis loss
c. copper loss
d. leakage loss
Electrons at the outer shell
a. inside shell electrons
b. conductor electrons
c. outside shell electrons
d. valence electrons
Solve for flux density (in
gauss) from a magnetic flux
of 5,000 Mx through a
perpendicular area of 2cm x
5cm
a. 5, 000G
b. 500G
c. 10, 000G
d. 50G
The property of the material
which opposes creation of
magnetic flux
a. resistance
b. permeance
c. reluctance
d. conductance
How many turns are needed
to produce a magnetizing
force of 5000At for a coil of
50 amperes?
a. 1, 000 turns
b. 5, 000 turns
c. 100 turns
d. 500 turns
When you increase the
resistance in a circuit the
flow of electrons will
___________
a. flow faster
b. be constant
c. be decreased
d. be stopped
What is residual
magnetism?
a.
the external magnetic field
when the current is flowing
through the exciting coil
b.
the flux density, which exists
in the iron core when the
magnetic field intensity, is
reduced to zero
c.
the flux density, which exists
in the iron core when the
magnetic field intensity, is at
its maximum value
d.
the flux density when the
magnetic core is saturated.
What is the law that
determines polarity of an
induced voltage?
a. Norton’s law
b. Thevenin’s law
c. Lenz’s law
d. Faraday’s law
The science of physical
phenomena at very low
temperature, approaching
absolute zero is called
_____________
a. crytanalysis
b. cybernetics
c. temperature inversion
d. cryogenics
What happens in the
resistance of copper wire
when its temperature is
raised?
a. decreased
b. steady
c. increased
d. zero
_______________
capability is analogous to
permeance
a. admittance
b. conductance
c. reluctance
d. resistance
What is the law whereby the
attraction or repulsion
between two magnetic poles
is directly proportional to
their strength?
a. Coulomb’s law
b. Newton’s law
c. Coulomb’s first law
d. Norton’s law
The particles that make up
the lattice in ionic crystal?
a. molecules
b. ions
c. electrons
d. neutrons
What do you call an
electromagnet with its core
in a form of magnetic ring?
a. paraboloid
b. solenoid
c. toroid
d. motor
___________ is the
procedure by which an atom
is given a net charge by
adding or taking away
electron
a. polarization
b. irradiation
c. ionization
d. doping
The unit of reluctance
a. Gauss
b. Weber
c. Maxwells
d. At/Wb
Find the dielectric constant
of air
a. approximately 1
b. approximately 0
c. approximately 2
d. approximately 4
Protons are about
____heavier than electrons
a. 1, 800 times
b. less than thrice
c. less
d. twice
Electric energy refers to
______________
a. joules divided by time
b. volt-coulomb
c. volt-ampere
d. watt
Refers to the lowest voltage
across any insulator that
can cause current flow
a. conduction voltage
b. breakdown voltage
c. voltage flow
d. voltage drop
The area of a conductor
whose diameter is 0.001
inch is equal to
a. one angstrom
b. one circular mil
c. one micron
d. one steradian