FUNDAMENTALS OF ELECTRICAL ENGINEERING [ ENT 163 ] LECTURE #6 MAGNETISM AND ELECTROMAGNETISM HASIMAH ALI Programme of Mechatronics, School of Mechatronics Engineering, UniMAP.

CONTENTS 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.

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). Unit is weber (Wb), where 1Wb = lines. Since weber is a very large unit, thus in most practical situation, microweber is used ( lines). Magnetic flux density is the amount of flux per unit area perpendicular to the magnetic field. Symbol denoted by B, unit tesla ( T). 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.

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. THE MAGNETIC FIELD

Further Reading Engineering Electromagnetism, Mcgraw Hill,6 th edition, William, Hayt Electric Circuit Fundamentals. (7th Edition), Floyd,Prentice Hall. (chapter 7).