south pole north pole sn magnet magnetic field. sn needle paper copper cable thumb nail
TRANSCRIPT
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SOUTH Pole
NORTHPole
SN
MAGNETMAGNETIC FIELD
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SN
NeedlePaper
Copper Cable
Thumb Nail
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MAGNETIC CIRCUIT, ELECTROMAGNETISM
AND ELECTROMAGNETICINDUCTION
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The end of lesson, students The end of lesson, students should be ;should be ;
Understand magnetism Understand the composite series magnetic
circuit Understand the electrical and magnetic
quantities Understand hysteresis Understand electromagnetism Determine the magnetic field direction. Understand electromagnetic induction
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iNTRoDUctIONiNTRoDUctION
MAGNET isthe material that have two poles NORTH and SOUTH
SN
SOUTH Pole
NORTHPole
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iNTRoDUctIONiNTRoDUctION
MAGNET can be define as
Material that can attract piece of iron or metal
SN
Needle
Thumb Nail
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iNTRoDUctIONiNTRoDUctIONMATERIAL that ATTRACTED by the MAGNET is known as
MAGNETIC SUBSTANCES
S
Needle
Thumb Nail
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iNTRoDUctIONiNTRoDUctIONThe ABILITY to ATTRACT the MAGNETIC SUBSTANCES is known as
MAGNETISM
S
Needle
Thumb Nail
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iNTRoDUctIONiNTRoDUctION
MAGNETIC FIELD is the force around the MAGNET which can attract any MAGNETIC MATERIAL around it.
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FLUX MAGNET is the line around the MAGNET bar which form MAGNETIC FIELD.
SN
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TYpEs of MAGNETTYpEs of MAGNET
There are 2 types of MAGNET
PURE MAGNETMANUFACTURE MAGNET
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PURE MAGNET
Known as MAGNET STONE
The stone ORIGINALY have the NATURAL MAGNETIC
Basically the stone is found in the form of IRON ORE
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MANUFACTURE MAGNET
There are 2 types of MANUFACTURE MAGNET
PERMANENT MAGNETTEMPORARY MAGNET
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PERMANENT MAGNET
The ABILITY of the MAGNET to kept its MAGNETISM
The basic shape of PERMANENT MAGNET
U shapehorseshoe RODCylinderBAR
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PERMANENT MAGNET
U shapeHorseshoe Rod
Cylinder
Bar
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Permanent magnet can be obtained by:naturally or magnetic induction ( metal rub against natural magnet)
placing a magnet into the coil and then supplied with a high electrical current.
PERMANENT MAGNET
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Permanent magnet used in small devices such as:
PERMANENT MAGNET
speakers metercompass
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TEMPORARY MAGNETTEMPORARY MAGNET
BECOME MAGNET only when there is CURRENT SUPPLY to the metal
It has magnetic properties when subjected to magnetic force and it will be lost when power is removed.
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TEMPORARY MAGNETTEMPORARY MAGNETExample :
relayelectric bells
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Magnetic flux lines have direction and pole.
The direction of movement outside of the magnetic field lines is from north to south.
CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).
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The strongest magnetic field are at the magnetic poles .
DIFFERENT POLES ATTRACT each other
SAME MAGNETIC POLES will REPEL each other
SN SN
SN S N
CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).
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FLUX form a complete loop and never intersect with each other.
FLUX will try to form a loop as small as possible.
SN
CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).
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MAGNETIC QUANTITY MAGNETIC QUANTITY CHARACTERISTICSCHARACTERISTICS
Magnetic Flux Magnetic flux is the amount of
magnetic field produced by a magnetic source.
The symbol for magnetic flux is . The unit for magnetic flux is the
weber, Wb.
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MAGNETIC QUANTITYMAGNETIC QUANTITYCHARACTERISTICSCHARACTERISTICS
Magnet Flux density The symbol for magnetic flux
density is B. The unit is tesla, T the unit for area A is m2 where
1 T = 1 Wb/m.
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MAGNETIC QUANTITY MAGNETIC QUANTITY CHARACTERISTICSCHARACTERISTICS
Magnet Flux density Magnetic flux density is the
amount of flux passing through a defined area that is perpendicular to the direction of flux
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MAGNETIC QUANTITY MAGNETIC QUANTITY CHARACTERISTICSCHARACTERISTICS
Magnetic flux density = area
flux magnetic
A
ΦB Tesla
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MAGNETIC QUANTITY MAGNETIC QUANTITY CHARACTERISTICSCHARACTERISTICS
Example 3
A magnetic pole face has rectangular section having dimensions 200mm by 100mm. If the total flux emerging from the pole is 150Wb, calculate the flux density.
A
ΦB
Area, A
Flux, Φ
B?
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MAGNETIC QUANTITY MAGNETIC QUANTITY CHARACTERISTICSCHARACTERISTICS
Solution 3Magnetic flux, = 150 Wb = 150 x 10-6 WbCross sectional area, A = 200mm x 100mm
= 20 000 x 10-6 m2
Flux density,
= 7.5 mT
6
6
1020000
10150
A
ΦB
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MAGNETOMOTIVE FORCE (MMF)MAGNETOMOTIVE FORCE (MMF) The force which creates the magnetic flux in a
magnetic circuit is called magnetomotive force (mmf)
- The mmf is produced when a current passes through a coil of wire. The mmf is the product of the number of turns(N) and current (I) through the coil.
Unit = Ampere Turns (A.T)
Formula , Fm = N x I
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MAGNETIC FIELD STRENGTH,H MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)(MAGNETISING FORCE)
Defined as magnetomotive force, Fm per metre length of measurement being ampere-turn per metre.
Current
l
NI
l
FH m
magnetomotive force
number of turns
average length of magnetic circuit
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MAGNETIC FIELD STRENGTH,H MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)(MAGNETISING FORCE)
Example 1
A current of 500mA is passed through a 600 turn coil wound of a toroid of mean diameter 10cm. Calculate the magnetic field strength.
l
NI
l
FH m
Current, I
Turn, N
Diameter, d
H?
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MAGNETIC FIELD STRENGTH,H MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)(MAGNETISING FORCE)
Solution 1I = 0.5AN= 600
l = x 10 x 10-2m
mATH
H
metreampereturnl
NIH
/81.9543142.0
5.0600
/
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MAGNETIC FIELD STRENGTH,H MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)(MAGNETISING FORCE)
Example 2
An iron ring has a cross-sectional area of 400 mm2. The coil resistance is 474 Ω and the supply voltage is 240 V and a mean diameter of 25 cm. it is wound with 500 turns. Calculate the magnetic field strength, H
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MAGNETIC FIELD STRENGTH,H MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)(MAGNETISING FORCE)
Solution 2I = V/ R = 240 / 474 = 0.506 Al = π D = π (25 x10-2) = 0.7854 m H=
H=
H= 322.13 AT/m
l
NI
7854.0
506.0500
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PERMEABILITYPERMEABILITYFor air, or any other non-
magnetic medium, the ratio of magnetic flux density to magnetic field strength is constant ,
This constant is called the permeability of free space and is equal to 4 x 10-7 H/m.
H
B
µ0
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PERMEABILITYPERMEABILITY
For any other non-magnetic medium, the ratio
For all media other than free space
r
rH
B 0
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PERMEABILITYPERMEABILITY
r is the relative permeability and is defined as
r varies with the type of magnetic material.
in vacuumdensity flux
materialin density flux r
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PERMEABILITYPERMEABILITY
r for a vacuum is 1 is called the absolute permeability.
The approximate range of values of relative permeability r for some common magnetic materials are :
Cast iron r = 100 – 250Mild steel r = 200 – 800Cast steelr = 300 – 900
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PERMEABILITYPERMEABILITY
Example 4
A flux density of 1.2 T is produced in a piece of cast steel by a magnetizing force of 1250 A/m. Find the relative permeability of the steel under these conditions.
HB r0
Flux density, B
H
µr?
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PERMEABILITYPERMEABILITY
Solution 4
HB r0
764
)1250)(104(
2.17
0
H
Br
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RELUCTANCERELUCTANCE
Reluctance,S is the magnetic resistance of a magnetic circuit to presence of magnetic flux.
Reluctance,
The unit for reluctance is 1/H or H-1 or A-T/Wb
AAHBBA
HlFS
r
m
0)/(
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RELUCTANCERELUCTANCEExample 5
Determine the reluctance of a piece of metal of length 150mm and cross sectional area is 1800mm2when the relative permeability is 4 000. Find also the absolute permeability of the metal.
S?
Length, l µrµ?
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RELUCTANCERELUCTANCESolution 5Reluctance,
= = 16 579 H-1
Absolute permeability, =
AS
r0
)101800)(4000)(104(
1015067
3
r 0)4000)(104( 7
= 5.027 x 10-3 H/m
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ELECTROMAGNETELECTROMAGNET Is a magnetic iron core
produced when the current flowing through the coil.
Thus, the magnetic field can be produced when there is a current flow through a conductor.
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The direction of the magnetic field can be determined using the method:
1. Right Hand Grip Rules 2. Maxwell's screw Law. 3. Compass
Three rules may be used to indicate the direction of the current and the flux produced by current carrying conductor.
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Right Hand Grip RuleRight Hand Grip Rule
is a physics principle applied to electric current passing through a solenoid, resulting in a magnetic field.
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Right Hand Grip RuleRight Hand Grip RuleWhen you wrap your right hand
around the solenoid
your fingers in the direction of the conventional current
your thumb points in the direction of the magnetic north pole
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Right Hand Grip RuleRight Hand Grip RuleIt can also be applied to
electricity passing through a straight wire
the thumb points in the direction of the conventional current (from +ve to -ve)
the fingers point in the direction of the magnetic lines of flux.
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Another way to determine the direction of the flux and current in a conductor is to use Maxwell's screw rule.
MAXWELL’S SCREW LAW
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a right-handed screw is turned so that it moves forward in the same direction as the current, its direction of rotation will give the direction of the magnetic field.
MAXWELL’S SCREW LAW
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Electromagnetic Effect Electromagnetic Effect Direction of Current
going INside Solenoid
Direction of Magnetic Flux around Solenoid
Direction of Current going OUTside
Solenoid
Direction of Magnetic Flux around Solenoid
Right Hand Grip Rule
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Electromagnetic Effect Direction of Current
going INside Solenoid
Direction of Magnetic Flux around Solenoid
Direction of Current going OUTside
Solenoid
Direction of Magnetic Flux around Solenoid
Same Direction Different Direction
Maxwell Screw Law
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Electromagnetic Effect Electromagnetic Effect
Factors that influence the strength of the magnetic field of a solenoid
The number of turns The value of current flow Types of conductors to produce
coil The thickness of the conductor
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ELECTROMAGNETIC INDUCTION ELECTROMAGNETIC INDUCTION Definition : When a conductor is moved
across a magnetic field so as to cut through the flux, an electromagnetic force (emf) is produced in the conductor.
This effect is known as electromagnetic induction.
The effect of electromagnetic induction will cause induced current.
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ELECTROMAGNETIC INDUCTION ELECTROMAGNETIC INDUCTION
2 laws of electromagnetic induction:i. Faraday’s lawii.Lenz’z Law
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Faraday’s lawFaraday’s lawIt is a relative movement of the magnetic
flux and the conductor then causes an emf and thus the current to be induced in the conductor.
Induced emf on the conductor could be produced by 2 methods flux cuts conductor or conductor cuts flux.
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Faraday’s lawFaraday’s lawFaraday’s First Law : Flux cuts conductor
When the magnet is moved towards the coil, a deflection is noted on the galvanometer showing that a current has been produced in the coil.
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Faraday’s lawFaraday’s lawFaraday’s Second Law :Conductor cuts flux
When the conductor is moved through a magnetic field . An emf is induced in the conductor and thus a source of emf is created between the ends of the conductor.
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Faraday’s lawFaraday’s lawThis induced electromagnetic field is given by E = Blv
volts
B=flux density, Tl =length of the conductor in the magnetic field, mv=conductor velocity, m/s
If the conductor moves at the angle to the magnetic field, then
E = Blv sin volts
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Faraday’s lawFaraday’s lawExample
A conductor 300mm long moves at a uniform speed of 4m/s at right-angles to a uniform magnetic field of flux density 1.25T. Determine the current flowing in the conductor when :
a. its ends are open-circuitedb. its ends are connected to a load of 20
resistance.
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Faraday’s lawFaraday’s lawSolution
a. If the ends of the conductor are open circuited no current will flow .
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Faraday’s lawFaraday’s lawSolution
b. E.m.f. can only produce a current if there is a closed circuit. When a conductor moves in a magnetic field it will have an e.m.f. induced.Induced e.m.f. , E = Blv
=(1.25)(0.3)(4) = 1.5 v
From Ohm’s law
mAI
I
R
EI
7520
5.1
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Lenz’z lawLenz’z lawThe direction of an induced emf is always
such that it tends to set up a current opposing the motion or the change of flux responsible for inducing that emf
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FormulaFormula
AS
r0
l
NI
l
FH m
A
ΦB
MAGNETIC FIELD STRENGTH
RELUCTANCE
MAGNETIC FLUX DENSITY
PERMEABILITY H
Br0
AAHBBA
HlFS
r
m
0)/(
MAGNETOMOTIVE FORCE (MMFMAGNETOMOTIVE FORCE (MMF), Fm = N x I
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Composite magnetic circuitA series magnetic circuit that has parts of different dimensions and material is called composite magnetic circuit.Each part will have its own reluctance. Total reluctance is equal to the sum of reluctances of individual parts.
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Total reluctanceTotal reluctance
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Comparison between magnetic Comparison between magnetic and electric circuitand electric circuit
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Similarities & dissimilarities between magnetic circuit and electric circuit
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Similarities & dissimilarities between magnetic circuit and electric circuit
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Hysterisis and hysterisis lossHysterisis and hysterisis loss
Figure 7.6
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