1. NORTH
Pole
SOUTH Pole N S
MAGNET
MAGNETIC FIELD

2. Needle
Paper S N
Thumb Nail
Copper Cable

3. MAGNETIC CIRCUIT, ELECTROMAGNETISM AND ELECTROMAGNETIC
INDUCTION

4. The end of lesson, students 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

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

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

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

8. iNTRoDUctION
The ABILITY to ATTRACT the MAGNETIC SUBSTANCES is known as
MAGNETISM
Needle S
Thumb Nail

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

10. FLUX MAGNET is the line around the MAGNET bar which form MAGNETIC FIELD.

11. PURE MAGNET MANUFACTURE MAGNET TYpEs of MAGNET
There are 2 types of MAGNET
PURE MAGNET
MANUFACTURE MAGNET

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

13. MANUFACTURE MAGNET PERMANENT MAGNET TEMPORARY MAGNET
There are 2 types of MANUFACTURE MAGNET
PERMANENT MAGNET
TEMPORARY MAGNET

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

15. PERMANENT MAGNET
Horseshoe
Rod
U shape
Cylinder
Bar

16. PERMANENT MAGNET 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.

17. PERMANENT MAGNET compass speakers meter
Permanent magnet used in small devices such as:
compass
speakers
meter

18. TEMPORARY 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.

19. TEMPORARY MAGNET
Example :
relay
electric bells

20. CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).
Magnetic flux lines have direction and pole.
The direction of movement outside of the magnetic field lines is from north to south.

21. CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).
The strongest magnetic field are at the magnetic poles . DIFFERENT POLES ATTRACT each other SAME MAGNETIC POLES will REPEL each other S N S N S N S N

22. CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).
FLUX form a complete loop and never intersect with each other.
FLUX will try to form a loop as small as possible. S N

23. MAGNETIC QUANTITY CHARACTERISTICS
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.

24. MAGNETIC QUANTITY CHARACTERISTICS
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.

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

26. MAGNETIC QUANTITY CHARACTERISTICS
Magnetic flux density =
Tesla

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

28. MAGNETIC QUANTITY CHARACTERISTICS
Solution 3
Magnetic flux,  = 150 Wb = 150 x 10-6 Wb
Cross sectional area, A = 200mm x 100mm
= x 10-6 m2
Flux density,
= 7.5 mT

29. Unit = Ampere Turns (A.T)
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

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

31. MAGNETIC FIELD STRENGTH,H (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.
Current, I
Turn, N
Diameter, d H?

32. MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)
Solution 1
I = 0.5A
N = 600
l =  x 10 x 10-2m

33. MAGNETIC FIELD STRENGTH,H (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

34. MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)
Solution 2
I = V/ R = 240 / 474 = A
l = π D = π (25 x10-2) = m H=
H= AT/m

35. PERMEABILITY
For 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. µ0

36. PERMEABILITY For any other non-magnetic medium, the ratio
For all media other than free space

37. PERMEABILITY
r is the relative permeability and is defined as r varies with the type of magnetic material.

38. PERMEABILITY 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 – 250
Mild steel r = 200 – 800
Cast steel r = 300 – 900

39. PERMEABILITY
Flux density, B
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. H
µr?

40. PERMEABILITY
Solution 4

41. 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-T/Wb

42. RELUCTANCE S?
Example 5 Determine the reluctance of a piece of metal of length 150mm and cross sectional area is 1800mm2when the relative permeability is Find also the absolute permeability of the metal.
Length, l µr µ?

43. RELUCTANCE = 5.027 x 10-3 H/m Solution 5 Reluctance,
Absolute permeability,
= x 10-3 H/m

44. ELECTROMAGNET
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.

45. 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.

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

47. Right Hand Grip Rule 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

48. Right Hand Grip Rule
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.

49. MAXWELL’S SCREW LAW
Another way to determine the direction of the flux and current in a conductor is to use Maxwell's screw rule.

50. MAXWELL’S SCREW LAW
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.

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

52. Electromagnetic Effect
Direction of Current going OUTside Solenoid
Direction of Current going INside Solenoid
Maxwell Screw Law
Same Direction
Different Direction
Direction of Magnetic Flux around Solenoid
Direction of Magnetic Flux around Solenoid

53. 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

54. 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.

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

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

57. Faraday’s law
Faraday’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.

58. Faraday’s law
Faraday’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.

59. 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

60. 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 :
its ends are open-circuited
its ends are connected to a load of 20  resistance.

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

62. 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)(0.3)(4)
= 1.5 v
From Ohm’s law

63. Lenz’z law
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

64. Formula MAGNETOMOTIVE FORCE (MMF), Fm = N x I MAGNETIC FIELD STRENGTH
MAGNETIC FLUX DENSITY
PERMEABILITY
RELUCTANCE

66. Composite magnetic circuit A 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.

67. Total reluctance

68. Comparison between magnetic and electric circuit

69. Similarities & dissimilarities between magnetic circuit and electric circuit

70. Similarities & dissimilarities between magnetic circuit and electric circuit

71. Hysterisis and hysterisis loss
Figure 7.6