microsoft powerpoint chapter 3 whit learning

SOUTH
Pole
NORTH
Pole
S
N
MAG
MAGNETIC
FIELDNET

Needle
Paper
S
N
Copper
Cable
Thumb Nail

❑ INTRODUCTION
❑ TYPES OF MAGNET
❑ BASIC MAGNET LAWS
❑ ELECTROMAGNETIC EFFECTS
❑ MAGNETIC FIELD STRENGTH
❑ MAGNETIC QUANTITY CHARACTERISTICS
❑ PERMEABILITY
❑ RELUCTANCE
❑ ELECTROMAGNETIC INDUCTION
CoNTents

MAGNET is
the material that have two poles NORTH and
SOUTH
iNTRoDUctION
S
N
SOUTH
Pole
NORTH
Pole

MAGNET can be define as
Material that can attract piece of iron
or metal
iNTRoDUctION
Needle
S
N
Thumb Nail

MATERIAL that ATTRACTED by the
MAGNET is known as
MAGNETIC SUBSTANCES
iNTRoDUctION
Needle
S
Thumb Nail

iNTRoDUctION
The ABILITY to ATTRACT the
MAGNETIC SUBSTANCES
is known aNseedle
MAGNETISM
S
Thumb Nail

MAGNETIC FIELD is
the force around the MAGNET which can
attract any MAGNETIC MATERIAL around
it.
iNTRoDUctION

FLUX MAGNET is the line around
the MAGNET bar which form MAGNETIC
FIELD.
iNTRoDUctION
S
N

TYpEs of MAGNET
There are 2 types of MAGNET
O
OMANUFACTURE MAGNET

PURE MAGNET
Known as MAGNET STONE
The stone ORIGINALY have the
NATURAL MAGNETIC
Basically the stone is found in the form
of IRON ORE

MANUFACTURE
MAGNET
There are 2 types of
MANUFACTURE MAGNET
OPERMANENT MAGNET
OTEMPORARY MAGNET

PERMANENT MAGNET
The ABILITY of the MAGNET to kept
its MAGNETISM
The basic shape of PERMANENT
MAGNET
O U shape
O horseshoe
O ROD
O Cylinder
O BAR

PERMANENT MAGNET
U shape
Horseshoe Rod
Cylinder
Bar

PERMANENT MAGNET
O 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 used in small devices such
as:
PERMANENT MAGNET
speakers meter
compass

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.
TEMPORARY MAGNET

O Example :
TEMPORARY MAGNET
relay
electric bells

BASIC MAGNET LAW
O Magnetic flux lines have direction and
pole.
O The direction of movement outside of the
magnetic field lines is from north to south.

BASIC MAGNET LAW
The strongest magnetic field are at the
magnetic poles .
N S
DIFFERENT POLES ATTRACT each other
S N
SAME MAGNETIC POLES will REJECT
each other
N S S N

BASIC MAGNET LAW
O FLUX form a complete loop and never
intersect with each other.
O FLUX will try to form a loop as small as
possible.
S
N

ELECTROMAGNET
O Is a magnetic iron
core produced when
the current flowing
through the coil.
O Thus, the magnetic
field can be produced
when there is a
current flow through a
conductor.

ELECTROMAGNET
The direction of the magnetic field can be
determined using the method:
1. Right Hand Grip Rules
2. Maxwell's screw Law.
Both rules may be used to indicate the
direction of the current and the flux
produced by current carrying
conductor.

Right Hand Grip Rule
O is a physics
principle applied to
electric current
passing through a
solenoid, resulting in
a magnetic field.

O When you wrap your right hand
around the solenoid
your thumb points
in the direction of
the magnetic
north pole
your fingers in the
direction of the
conventional
current

O It 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.

O 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

O 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

Electromagnetic Effect
Direction of Magnetic
Flux around Solenoid
Direction of Current
going INside
Solenoid
going OUTside
Solenoid
Right Hand Grip
Rule

going INside
Solenoid
going OUTside
Solenoid
Maxwell Screw Law
Different Direction
Same Direction

Factors that influence the strength of the
magnetic field of a solenoid
O The number of turns
O The value of current flow
O Types of conductors to produce coil
O The thickness of the conductor

ELECTROMAGNETIC
INDUCTION
O 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.
O This effect is known as
electromagnetic induction.
O The effect of electromagnetic
induction will cause induced current.

ELECTROMAGNETIC
INDUCTION
2 laws of electromagnetic
induction:
i. Faraday’s law
ii.Lenz’z Law

Faraday’s law
O It 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.
O Induced emf on the conductor could
be produced by 2 methods
• flux cuts conductor or
• conductor cuts flux.

Faraday’s 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.

Faraday’s 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.

Faraday’s law
This induced electromagnetic field is given
by E = Blv volts
B =flux density, T
l =length of the conductor in the magnetic field,
m v =conductor velocity, m/s
If the conductor moves at the angle
 to the magnetic field, then
E = Blv sin volts

Faraday’s law
Example
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-circuited
b. its ends are connected to a load of
20 
resistance.

Faraday’s law
Solution
a. If the ends of the conductor are
open circuited no current will flow .

Faraday’s law
Solution
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)(300m)(4)
= 1.5 v
From Ohm’s law
E
R
1 .
5
I 
I 
20
I  75 mA

O The 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
Lenz’z law

MAGNETIC FIELD STRENGTH,H
(MAGNETISING FORCE)
O Defined as magnetomotive force, Fm
per metre length of measurement
being ampere-turn per metre.
l l

NI
magnetomotive force
F
H
 m
number of turns
Current
average length of magnetic circuit

Example 1
A current of 500mA is passed
Current, I
(MAGNETISING FORCE)
through a 600 turn coil wound of a
toroid of mean diameter 10cm.
Calculate the magnetic field
strength.
Turn, N
H? l
Diameter, d
H 
Fm

NI
l

(MAGNETISING FORCE)
Solution 1
I = 0.5A
N = 600
l =  x 10 x 10-
2m
H
/ metre
ampereturn
l
H  954 .81 AT / m
NI
H


600  0 .5
0 .3142

Example 2 Area,
A
Diameter, d
(MAGNETISING FORCE)
is 474 Ω and the supply voltage is
An iron ring has a cross-sectional
Resistance,area of 400 mm2. The coil resistance
R
Voltage, V
Turn,N
l l
240 V and a mean diameter of 25 cm.
it is wound with 500 turns. Calculate
the magnetic field strength, H ?
H 
Fm

NI

(MAGNETISING FORCE)
Solution 2
I = V/ R = 240 / 474 = 0.506 A
l = π D = π (25 x10-2) = 0.7854 m
H=
H=
H= 322.13 AT/m
NI
l
500  0 .
506
0 . 7854

MAGNETIC QUANTITY
CHARACTERISTICS
Magnetic Flux
O Magnetic flux is the amount of
magnetic filed produced by a
magnetic source.
O The symbol for magnetic flux is
.
O The unit for magnetic flux is the
weber, Wb.

MAGNETIC QUANTITY
CHARACTERISTICS
Magnet Flux density
O Magnetic flux density is the amount
of flux passing through a
defined area that is
perpendicular to the direction of
flux

MAGNETIC QUANTITY
CHARACTERISTICS
Magnet Flux density
O The symbol for magnetic flux density
is B.
O The unit is tesla, T and t
O the unit for area A is m2 where
1 T = 1 Wb/m.

MAGNETIC QUANTITY
CHARACTERISTICS
Magnetic flux density = magneticflux
area
A
Φ
B

Tesla

MAGNETIC QUANTITY
CHARACTERISTICS
Example 3
A magnetic pole face has rectangular
Area,
A
section having dimensions 200mm by
100mm. If the total flux emerging from
the pole is 150Wb, calculate the
flux density.
Flux, Φ
B? A
Φ
B 

MAGNETIC QUANTITY
CHARACTERISTICS
Solution 3
Magnetic flux,  = 150 Wb = 150 x 10-6
Wb Cross sectional area, A= 200mm x
100mm
= 20 000 x 10-6 m2
= 7.5 mT
A 20000106
Φ 150106

Flux density, B 

PERMEABILITY
constant ,
O This constant is called the
permeability of free space and is
equal to 4 x 10-7 H/m.
µ0

H
O For air, or any other non-magnetic
medium, the ratio of magnetic flux
density to magnetic field strength is
B


PERMEABILITY
O For any other non-magnetic medium,
the ratio
r

O For all media other than free space
H
0 r
B
 


PERMEABILITY
r is the relative permeability and
is defined as

flux density in material
r varies with the type of
magnetic material.
flux density in vacuum
r

PERMEABILITY
r for a vacuum is 1 is called
the absolute permeability.
The approximate range of values of
relative permeability rfor some
common magnetic materials are :
r = 100 –
250
O Cast iron
O Mild steel
O Cast steel
r = 200 –
800
r = 300 –
900

PERMEABILITY
Example 4
A flux density of 1.2 T is produced
Flux density,
B
in a piece of cast steel by a
magnetizing force of 1250 A/m.
Find the relative permeability of
the steel under these conditions.
H
µr? B 
0r H

PERMEABILITY
Solution 4
B   0 
r H
= 764
1.2
0
 
 H (4 102
)
(1250)
B
r

RELUCTANCE
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/Wb
 0  r
A
Hl
Fm l
l
 BA ( B / H ) A
S   


RELUCTANCE
Example 5
Determine the reluctance of a piece of
S?
Length, l
metal of length 150mm when the
relative permeability is 4 000. Find
also the absolute permeability of the
metal.
µ
r
µ?

RELUCTANCE
Solution 5
Reluctance, S
 r
l
=
 0  A
150 10 3
(4 10 7
)(4000)(1800 10 6
)
= 16 580 H-1
Absolute permeability,
   0  r
=
(4 107
)(4000)
= 5.027 x 10-3 H/m

Practice Make Perfect
HOMEWORK
4

Formula
l

NI
l
F
H  m
MAGNETIC FIELD STRENGTH
Φ
B

MAGNETIC FLUX DENSITY
0 r
A
S 
l
RELUCTANCE
A
PERMEABILITY
H
0 r
B
  


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