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EET103 TEKNOLOGI ELEKTRIK
KEMAGNETAN DAN
KEELEKTROMAGNETAN
Magnetism And Electromagnetism
Kemagnetan dan keelektromagnetan
• Kemagnetan: magnet, medan magnet dan
fluks, domain magnet, magnet kekal, magnet
sementara.
• Keelektromagnetan: medan magnet dan arus
elektrik, daya gerak magnet dan ketepuan,
keengganan litar magnet, kuantiti dan unit
magnetik, histerisis, daya elektromagnet, kilas
dalam gegelung.
• Aruhan elektromagnet: voltan aruhan dalam
gegelung, hukum lenz dan aturan tangan kanan
flemming, dan arus pusar.
KEMAGNETAN: MAGNET
• Magnetism: a force field that acts on some
materials but not on the materials
• Magnets: physical devices that possess
magnetism
• Lodestone: natural magnet
KEMAGNETAN: MEDAN MAGNET
DAN FLUKS
• Magnetic field: the force of magnetism
• Flux (Φ): invisible lines of force that make
up the magnetic field
• Magnetic field is strongest at the ends of the
magnet.
Medan Magnet dan Fluks
• Most magnets have a north pole and a
south pole.
• Flux leaves the north pole and enters the
south pole.
• Like poles repel; unlike poles attract.
Creation of poles
• Each time the magnet is broken, a new pair of
poles is created
Reaction of Like Poles
S
N
N
S
Like poles produce a repelling force on
these held-in-place magnets. The flux
loops are distorted.
Reaction of Like Poles
S
N
N
S
Like poles produce a repelling force
on these held-in-place magnets.
When freed, the magnets move apart
and the distortion decreases.
Reaction of Like Poles
S
N
N
S
Like poles produce a repelling force.
The magnets move apart and the distortion decreases.
Reaction of Like Poles
S
N
N
S
Like poles produce a repelling force.
The magnets move apart and the distortion decreases.
Reaction of unlike poles
• Unlike poles attract
each other.
• The force of attraction
is greatest when the
poles are touching.
KEMAGNETAN: DOMAIN MAGNET,
MAGNET KEKAL DAN MAGNET
SEMENTARA
• Magnetic materials: materials that are attracted by
magnetic fields
• Common magnetic materials: iron, iron compounds
and alloys containing iron or steel
• Nonmagnetic materials: materials that are not
attracted by magnets
• Nonmagnetic materials does not stop magnetic flux
• Magnetic materials have magnetic domains.
• Current-carrying conductors produce magnetic fields
Magnetic Domains in a Magnetic Field
(case 1)
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
TEMPORAR
Y MAGNET
Domains are randomly arranged in this
unmagnetized temporary magnetic material.
When subjected to a magnetic force field,
the domains are aligned with the field.
When the magnetic force field is removed,
the domains return to a random arrangement.
Magnetic Domains in a Magnetic Field
(case 2)
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
N
S
PERMANEN
TMAGNET
Domains are randomly arranged in this
unmagnetized permanent magnetic material.
When subjected to a magnetic force field,
the domains are aligned with the field.
When the magnetic force field is removed,
the domains remain aligned.
Kemagnetan dan keelektromagnetan
• Kemagnetan: magnet, medan magnet dan fluks,
domain magnet, magnet kekal, magnet
sementara.
• Keelektromagnetan: medan magnet dan arus
elektrik, daya elektromagnet, daya gerak
magnet dan ketepuan, keengganan litar
magnet, kuantiti dan unit magnetik, histerisis,
daya elektromagnet, kilas dalam gegelung
• Aruhan elektromagnet: voltan aruhan dalam
gegelung, hukum lenz dan aturan tangan kanan
flemming, dan arus pusar, histerisis, kilas dalam
gegelung.
KEELEKTROMAGNETAN: MEDAN
MAGNET DAN ARUS ELEKTRIK
• Electromagnetism:
production of a
magnetic field by
current flowing in a
conductor.
• The magnetic field
has no poles.
Dot: current flowing
out
cross: current flowing
in
Current in a conductor produces flux around the conductor.
A larger current produces more flux.




Conductor
Use the left-hand rule to determine
the direction of the flux.
Left hand rule
• The direction of the flux around a
conductor can be determined by using:
Force between conductors
Flux Around Parallel Conductors






The conductors repel
each other when
the currents are in
opposite directions.
Flux Around Parallel Conductors
The conductors repel each other when
the currents are in opposite directions.






Flux Around Parallel Conductors
The conductors repel each other when
the currents are in opposite directions.






Flux Around Parallel Conductors
The conductors repel each other when
the currents are in opposite directions.






Flux Around Parallel Conductors
The conductors attract each other when
the currents are in the same direction.




Flux Around Parallel Conductors
The conductors attract each other when
the currents are in the same direction.


Flux Around Parallel Conductors
The conductors attract each other when
the currents are in the same direction.


Coils
• The magnetic field around a straight wire is not
very strong.
• A strong field can be made by coiling the wire
around a piece of soft iron.
• This electromagnet is sometimes called a
solenoid.
• The shape of the magnetic field is the same as a
bar magnet.
Left hand rule
for coils
Coils
• The strength of the magnetic field around the coil
can be increased by:
1. Using a soft iron core (core means middle bit).
2. Using more turns of wire on the coil.
3. Using a bigger current.
• Reversing the direction of the current
will reverse the magnetic field direction.
KEELEKTROMAGNETAN: DAYA
GERAK MAGNET DAN KETEPUAN
• Daya gerak magnet (magnetomotive force,
mmf): effort exerted in creating a magnetic
field
• Ketepuan (saturation): A magnetic material
is saturated when an increase in mmf no
longer increase the flux in the material.
KEELEKTROMAGNETAN:
KEENGGANAN LITAR MAGNET
• Reluctance (keengganan litar magnet):
opposition to magnetic flux
• Magnetic materials are attracted to a
magnet because of their low reluctance
• Permeability: refers to a material's ability to
attract and conduct magnetic lines of flux
Low Reluctance Flux Path
Iron
Flux
Flux bends to follow a low reluctance path.
Adding a Low-Reluctance Path in
a Magnetic Field
N
S
Opposite magnetic poles produce a flux
in the air between the poles.
When a low-reluctance path is provided,
the flux increases and is concentrated in
the low-reluctance path.
KEELEKTROMAGNETAN: KUANTITI
DAN UNIT MAGNETIK
QUANTITIES
UNITS
magnetomotive force (mmf)
ampere-turn (At)
magnetic field strength (H)
ampere-turn/meter (At/m)
flux (f)
weber (Wb)
flux density (B)
tesla (T)
permeability (m)
Wb/(Atm)
relative permeability (µr)
unitless
Magnetomotive force (mmf)
• Base unit: ampere-turn (At)
• One ampere-turn is the mmf created by 1A
flowing through one turn of a coil.
Magnetic Field Strength (H)
• Magnetic field strength = field intensity =
magnetizing force
• Amount of mmf available to create a magnetic
field for each unit length of a magnetic circuit.
• Base unit: ampere-turn per meter (At/m)
mmf(A  t)
H
length(m)
Magnetic Field Strength (H)
4t
mmf = 3 A x 8 t = 24 At
8t
3A
Core length = 0.4 m
mmf = 3 A x 4 t = 12 At
24 At
H=
= 60 At / m
0.4 m
3A
Core length = 0.2 m
H=
12 At
0.2 m
= 60 At / m
The magnetic field strength is the same for the two circuits.
Flux (Φ)
• Base unit: Weber (Wb)
• One weber is the amount of flux change
required in 1s to induce 1V in a single
conductor.
Flux Density (B)
• Flux density: the amount of flux per unit
cross-sectional area
• Base unit: Tesla (T)
• One tesla is equal to one weber per square
meter.
flux(Wb)
Flux density(T) 
2
area(m )
Flux Density (B)
A
B
Material B carries twice as much flux as material A.
However, the flux density (B) is the same in both
materials because the cross-sectional area of B is two
times larger than that of A.
Permeability (µ)
• Permeability (µ): refers to ability of a
material to conduct flux
• Base unit: weber per ampere-turn-meter
(Wb/Atm)
Flux density(B)
Permeabili ty( m ) 
magnetic field strength(H )
Relative permeability (µr)
• Relative permeability (µr): compares the
permeability of the material with the air
• Example: µr of iron = 600 (iron carries 600
times as much flux as an equal amount of
air)
KEELEKTROMAGNETAN:
HISTERISIS
• Hysteresis is the tendency of a magnetic
material to retain its magnetization.
• Hysteresis causes the graph of magnetic
flux density versus magnetizing force to
form a loop rather than a line.
• The area of the loop represents the
difference between energy stored and
energy released per unit volume of
material per cycle. This difference is
called hysteresis loss.
Hysteresis loop
Hysteresis
• Retentivity - material's ability to retain a certain
amount of residual magnetic field when the
magnetizing force is removed after achieving
saturation. (The value of B at point B on the
hysteresis curve.)
• Coercive Force - The amount of reverse
magnetic field which must be applied to a
magnetic material to make the magnetic flux
return to zero. (The value of H at point C on the
hysteresis curve.)
KEELEKTROMAGNETAN: DAYA
ELEKTROMAGNET
• Motor effect: the force on a wire in a magnetic field
when current flows through the wire
• One side of the wire, the fields have the same
direction and repel the wire
• On the other side, the field have opposite
directions and attract the wire.
• We can predict which way the wire will move by
using Fleming’s Left Hand Rule
Motor effect (catapult effect)
Gambarajah ini
menggunakan
right hand rule!
Flemming’s Left Hand Rule (Motor
Rule)
• Use: To determine the direction of a force on a
current carrying conductor in a magnetic field
• The carbon rod is NOT magnetic.
• When no current flows, the rod is stationary
• When we turn on the current, the rod
experiences a force that makes it move.
• The direction of the force is determined by
Fleming' Left Hand Rule
KEELEKTROMAGNETAN: KILAS
DALAM GEGELUNG
• B – magnetic field
• F – Force
• Use Fleming’s left hand
rule to determine F
• No current flow
• Because of
momentum, the coil will
spin
• There is current flow,
therefore there is F.
Torque in coil
• The torque in coils can be determine:
T  Fd
T  Torque (Nm)
F  Force (N)
d  distance of F (m)
Kemagnetan dan keelektromagnetan
• Kemagnetan: magnet, medan magnet dan fluks,
domain magnet, magnet kekal, magnet sementara.
• Keelektromagnetan: medan magnet dan arus
elektrik, daya elektromagnet, daya gerak magnet
dan ketumpatan, keengganan litar magnet, kuantiti
dan unit magnetik, histerisis, daya elektromagnet,
kilas dalam gegelung
• Aruhan elektromagnet: voltan aruhan dalam
gegelung, hukum lenz dan aturan tangan kanan
flemming
ARUHAN ELEKTROMAGNET: VOLTAN
ARUHAN DALAM GEGELUNG
Induced Voltage

X
Voltage is induced when conductors cut lines of flux.
Green arrow shows direction of conductor movement.
Dot and X show direction of current caused by voltage.
No voltage is induced when conductors move parallel
to the to the lines of flux.
FARADAY’S LAW
If current produces a
magnetic field, why can't a
magnetic field produce a
current ?
Michael Faraday
In 1831 two people, Michael Faraday in
the UK and Joseph Henry in the US
performed experiments that clearly
demonstrated that a changing magnetic
field produces an induced EMF (voltage)
that would produce a current if the circuit
was complete.
• When the switch was closed, a momentary deflection was
noticed in the galvanometer after which the current
returned to zero.
• When the switch was opened, the galvanometer deflected
again momentarily, in the other direction. Current was not
detected in the secondary circuit when the switch was left
closed.
• When the switch is closed, the current begins to flow and
an induced magnetic field is set up around the primary
coil. The current increases from zero to some value over a
short period of time. The changing electrical current
produced a changing magnetic field which is the cause of
the induced current.
• When the switch is opened, the current decreases which
results in a decreasing magnetic field. The result is an
induced current in the secondary circuit, in the opposite
direction. When a constant current flows in the primary
circuit, the induced magnetic field is constant. A constant
magnetic field does not induce a current in the secondary
circuit.
An e.m.f. is made to happen (or induced) in a
conductor (like a piece of metal) whenever it
'cuts' magnetic field lines by moving across
them. This does not work when it is stationary. If
the conductor is part of a complete circuit a
current is also produced.
• Faraday found that the induced e.m.f. increases if
(i) the speed of motion of the magnet or coil increases.
(ii) the number of turns on the coil is made larger.
(iii) the strength of the magnet is increased.
Faraday’s Law
f
EN
Δt
• E = Electromotive force (emf)
• Φ = Flux
• t = Number of turn
• Any change in the magnetic environment of a coil of wire
will cause a voltage (emf) to be "induced" in the coil. No
matter how the change is produced, the voltage will be
generated.
• The change could be produced by changing the magnetic
field strength, moving a magnet toward or away from the
coil, moving the coil into or out of the magnetic field,
rotating the coil relative to the magnet, etc.
• Inserting a magnet into a coil
also produces an induced
voltage or current.
• The faster speed of insertion/
retraction, the higher the
induced voltage.
ARUHAN ELEKTROMAGNET:
HUKUM LENZ
Lenz's Law states that the
induced current will always set
up a magnetic field that will
oppose the movement of the
external magnetic field
Heinrich Friedrich
Emil Lenz
• Therefore, if we move a bar magnet through a coil of wire,
according to Lenz's Law, the generated magnetic field
("effort") will oppose the magnetic field of the bar magnet
(The "cause" that produced the induced current with its
associated magnetic field).
Lenz Law experiment:
• A small force acting on the magnet causes a
changing magnetic field in the coil which will
induce a current.
• If the current flowed in the indicated direction, an
induced magnetic field would put the south pole
opposite the north pole in the external magnet.
• This would attract the magnet, causing it to
accelerate. The increased speed of the magnet
would induce a larger current which would pull
even harder on the magnet and so on.
• If we think about this situation, we see that a small
amount of work input generates a larger output of
energy. This arrangement would violate the law of
conservation of energy
• If the induced current flows in the opposite direction, the
induced current in the coil would set up a magnetic field
with the north pole opposite to the external magnet.
• In order to generate a current, we would have to exert a
force that would be opposed by the induced magnetic
field.
• The harder we push on the magnet, the more repulsion
we'd feel from the induced magnetic field.
• To increase the energy output, we would need to increase
the work input. This would be consistent with what we
know about the law of conservation of energy.
Flemming’s Right hand rule
(Generator Rule)
• Use: To determine the direction of the induced
emf/current of a conductor moving in a magnetic
field.