Physics
Permanent and Induced Magnetism
Permanent magnetism refers to the inherent magnetic properties of certain materials, such as iron or steel, that can retain their magnetization without an external magnetic field. Induced magnetism, on the other hand, occurs when a material becomes magnetized in the presence of an external magnetic field but loses its magnetization when the field is removed.
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5 Key excerpts on "Permanent and Induced Magnetism"
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
6. Note the distinctive magnetic characteristics for both soft and hard magnetic materials. 7. Describe the phenomenon of superconductivity. Magnetism—the phenomenon by which materials exert an attractive or repulsive force or influence on other materials—has been known for thousands of years. However, the underlying principles and mechanisms that explain magnetic phenomena are complex and subtle, and their understanding has eluded scientists until relatively recent times. Many modern technological devices rely on magnetism and magnetic materials, including electrical power generators and transformers, electric motors, radio, television, tele- phones, computers, and components of sound and video reproduction systems. Iron, some steels, and the naturally occurring mineral lodestone are well-known examples of materials that exhibit magnetic properties. Not so familiar, however, is the fact that all substances are influenced to one degree or another by the presence of a magnetic field. This chapter provides a brief description of the origin of magnetic fields and discusses magnetic field vectors and magnetic parameters; diamagnetism, paramagnetism, ferromagnetism, and ferrimagnetism; different magnetic materials; and superconductivity. Magnetic Dipoles Magnetic forces are generated by moving electrically charged particles; these magnetic forces are in addition to any electrostatic forces that may exist. Often it is convenient to think of magnetic forces in terms of fields. Imaginary lines of force may be drawn to indicate the direction of the force at positions in the vicinity of the field source. The magnetic field distributions as indicated by lines of force are shown for a current loop and a bar magnet in Figure 18.1. Magnetic dipoles are found to exist in magnetic materials and in some respects are analogous to electric dipoles (Section 12.19).
- Robert J. Naumann(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
25 Magnetism and Magnetic Materials Magnetism may be thought of as electricity in motion. It is actually a relativistic effect of moving charges according to Einstein ’ s special theory of relativity. One observes a mag-netic fi eld in a reference frame that electrons are fl owing through, but in a reference frame that moves with the electrons, one observes only an electric fi eld. Natural ferromagnets in the form of loadstones were known to the ancient Chinese who used them for navigation. Hans Christian Ørsted was the fi rst person to connect magnetism with electricity when he noticed that a fl owing current in fl uenced a compass needle. Magnetic materials continue to play an ever increasing role in our modern technical society. For example, the recent discovery of low-cost iron-neodymium-boron magnets has made it possible to build highly ef fi cient permanent magnet motors that are used in hybrid vehicles and will be used in future electric vehicles. Another example is the continued development of magnetic storage media, which have extended hard drive storage capaci-ties far beyond what anyone would have expected a decade ago and have made high performance computers affordable to almost everyone. In order to understand how these materials function, we need to start with some basic principles. 25.1 Basic Relationships Just as the capacitance was increased when a dielectric with polarization P was placed between the plates of a capacitor, the magnetic fi eld in, or in the vicinity of, a material is altered by the magnetization M of the material. By analogy with the electric fi eld case in which we wrote D ¼ « E , we can write for the case of the magnetism B ¼ m H , where H is the applied magnetic fi eld (A = m), B is the resulting fl ux density (V s = m 2 ¼ Wb = m 2 ¼ T), and m is the permeability of the medium.
eBook - PDFGeneral Engineering Science in SI Units
The Commonwealth and International Library: Mechanical Engineering Division
- G. W. Marr, N. Hiller(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
Section 8 Electromagnetism 8.1. Introduction Before we consider the magnetic effect of an electric current, which is the main subject of this section, it will be helpful if we first of all deal very briefly with the phenomenon of permanent magnetism. 8.2. Permanent Magnetism This phenomenon was first recorded by the Greeks following on their observations of the behaviour of lodestone, a naturally occurring material which acts as a magnet. Most magnets are produced artificially, however, from iron or steel. The distin-guishing characteristics of a magnet are its ability to attract to itself other pieces of iron, and its ability to settle, when free to do so, with its magnetic axis lying in a north-south direction. These effects can be demonstrated very clearly by the simple bar type of permanent magnet. When such a magnet is dipped into a pile of small steel tacks or a heap of iron filings, and then withdrawn, a considerable quantity of tacks or filings are seen to adhere to the magnet. It is further observed that most of the tacks or filings are clustered near the ends of the bar magnet and that relatively few adhere near to the centre. This observation led to the early belief that the 148 I3LECTROMAGNETISM magnetism was concentrated in two centres near the ends of the magnet. These centres were called the poles of the magnet. When the bar magnet is suspended in a horizontal plane, it will settle with its axis lying in a north-south direction (Fig. 8.1). The end, or pole, which points towards the north is called the north-seeking pole, or more simply, the north pole; the other North seeking pole FIG. 8.1. pole is called the south pole. This property was first turned to practical advantage by the Chinese who developed the first com-pass. It is not our purpose to discuss, at this stage, present day theories about the mechanism of permanent magnets, but it must be emphasized that a single magnetic pole cannot exist.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
4. In terms of crystal structure, explain the source of ferrimagnetism for cubic ferrites. 5. (a) Describe magnetic hysteresis; (b) explain why ferromagnetic and ferrimagnetic ma- terials experience magnetic hysteresis; and (c) explain why these materials may become permanent magnets. 6. Note the distinctive magnetic characteristics for both soft and hard magnetic materials. 7. Describe the phenomenon of superconductivity. Magnetism—the phenomenon by which materials exert an attractive or repulsive force or influence on other materials—has been known for thousands of years. However, the underlying principles and mechanisms that explain magnetic phenomena are complex and subtle, and their understanding has eluded scientists until relatively recent times. Many modern technological devices rely on magnetism and magnetic materials, including electrical power generators and transformers, electric motors, radio, television, tele- phones, computers, and components of sound and video reproduction systems. Iron, some steels, and the naturally occurring mineral lodestone are well-known examples of materials that exhibit magnetic properties. Not so familiar, however, is the fact that all substances are influenced to one degree or another by the presence of a mag- netic field. This chapter provides a brief description of the origin of magnetic fields and discusses magnetic field vectors and magnetic parameters; diamagnetism, paramagnetism, ferromagnetism, and ferrimagnetism; different magnetic materials; and superconductivity. 18.1 | | INTRODUCTION 18.2 | | BASIC CONCEPTS Magnetic Dipoles Magnetic forces are generated by moving electrically charged particles; these magnetic forces are in addition to any electrostatic forces that may exist. Often it is convenient to think of magnetic forces in terms of fields. Imaginary lines of force may be drawn to indicate the direction of the force at positions in the vicinity of the field source.
eBook - PDFGeneral Engineering Science in SI Units
In Two Volumes
- G. W. Marr, N. Hiller(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
Section 8 Electromagnetism 8.1. Introduction Before we consider the magnetic effect of an electric current, which is the main subject of this section, it will be helpful if we first of all deal very briefly with the phenomenon of permanent magnetism. 8.2. Permanent Magnetism This phenomenon was first recorded by the Greeks following on their observations of the behaviour of lodestone, a naturally occurring material which acts as a magnet. Most magnets are produced artificially, however, from iron or steel. The distin-guishing characteristics of a magnet are its ability to attract to itself other pieces of iron, and its ability to settle, when free to do so, with its magnetic axis lying in a north-south direction. These effects can be demonstrated very clearly by the simple bar type of permanent magnet. When such a magnet is dipped into a pile of small steel tacks or a heap of iron filings, and then withdrawn, a considerable quantity of tacks or filings are seen to adhere to the magnet. It is further observed that most of the tacks or filings are clustered near the ends of the bar magnet and that relatively few adhere near to the centre. This observation led to the early belief that the 148 ELECTROMAGNETISM magnetism was concentrated in two centres near the ends of the magnet. These centres were called the poles of the magnet. When the bar magnet is suspended in a horizontal plane, it will settle with its axis lying in a north-south direction (Fig. 8.1). The end, or pole, which points towards the north is called the north-seeking pole, or more simply, the north pole; the other North seeking pole South seeking pole FIG. 8.1. pole is called the south pole. This property was first turned to practical advantage by the Chinese who developed the first com-pass. It is not our purpose to discuss, at this stage, present day theories about the mechanism of permanent magnets, but it must be emphasized that a single magnetic pole cannot exist.
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