FUNDAMENTALS OF ELECTRICAL
ENGINEERING
[ ENT 163 ]
LECTURE #6
MAGNETISM AND ELECTROMAGNETISM
HASIMAH ALI
Programme of Mechatronics,
School of Mechatronics Engineering, UniMAP.
Email: hashimah@unimap.edu.my
CONTENTS
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Introduction
The Magnetic Field
Electromagnetism
Electromagnetic Devices
Magnetic Hysteresis
Electromagnetic Induction
INTRODUCTION
• The operation of many types of electrical devices is based partially
on magnetic or electromagnetic principles.
• Basic principles in magnetism and electromagnetism – magnetic
field , magnetic flux, magnetic flux density, magnetic quantity and
units, magnetic hysteresis, electromagnetic induction.
THE MAGNETIC FIELD
Magnetic field is a force field that cats on some materials, also known
as magnetism.
• Magnet : physical devices that possess magnetic field.
• A permanent magnetic field – has a magnetic field surrounding it.
• Magnetic field – consists of the line of force, or flux lines that
radiate from the north pole (N) to the south pole (S) and back to
the north pole through the magnet material.
• This effectively forms a continuous magnetic field surrounding the
magnet.
• When unlike poles of two permanent magnets are placed
together, an attractive force is produced by the magnetic fields.
• When two like poles are brought close together , they repel each
other.
THE MAGNETIC FIELD
• When nonmagnetic material (e.g. paper, glass, wood, plastic) is
placed in a magnetic field, the lines of force are unaltered.
• When a magnetic material (e.g iron) is plced in the magnetic
field, the line of force tend to change course and pass through
the iron rather than through the surrounding air.
• The reason is the iron provides a magnetic path that is more
easily established than that of air.
• Therefore the iron would easily attracted to the magnet.
THE MAGNETIC FIELD
Magnetic flux is defined as the group of force lines going from the
north pole to the south pole of a magnetic. Symbol as ø (phi)
• The number of the lines of force in a magnetic field determines
the value of the flux (the more the lines of force, the greater the
flux and the stronger the magnetic field).
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• Unit is weber (Wb), where 1Wb = 10 lines.
• Since weber is a very large unit, thus in most practical situation,
microweber is used ( 1Wb  100 lines).
Magnetic flux density is the amount of flux per unit area perpendicular to
the magnetic field. Symbol denoted by B, unit tesla ( T).
B

A
Ø  flux,
A  cross sectional area of the magnetic
field.
THE MAGNETIC FIELD
How materials become magnetized:
• Ferromagnetism is phenomenon by which a material can exhibit a
spontaneous magnetization.
• Ferromagnetic material such as iron, nickel and cobalt become
magnetized when placed in the magnetic field of magnet.
• For example permanent magnet pick up paper clips, nails, iron
fillings and etc.
• In these cases, the object becomes magnetized. For example its
becomes a magnet itself under the influence of the permanent
magnetic field and becomes attracted to the magnet.
• When removed from the magnetic field, the object tends to lose its
magnetism.
THE MAGNETIC FIELD
• Phenomenon – ferromagnetic materials have magnetic
domains created within their atomic structure by the orbital
motion and spin of electrons.
• Domains – can be viewed as very small bar magnets with
north and south poles.
• When the material is not exposed to an external magnetic
field, the magnetic domains are randomly oriented.
• When the material is placed in a magnetic field, the domains
aligned themselves, thus becomes a magnet.
• Application: magnetic switch and alarm system.
Further Reading
Engineering Electromagnetism, Mcgraw Hill,6th edition, William, Hayt
Electric Circuit Fundamentals. (7th Edition), Floyd,Prentice Hall.
(chapter 7).