Physics
Magnetism and Electromagnetic Induction
Magnetism is the force exerted by magnets and moving charges. Electromagnetic induction is the process of generating an electromotive force in a closed circuit by varying the magnetic field around it. These phenomena are fundamental to understanding the behavior of electric currents and the operation of devices such as generators and transformers.
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10 Key excerpts on "Magnetism and Electromagnetic Induction"
- J. Felipe de Almeida(Author)
- 2021(Publication Date)
- Editora Dialética(Publisher)
CHAPTER 2 - ELECTRICITY, Magnetism and Electromagnetic InductionThe phenomena of electricity and magnetism originate in a behavior of elemental matter known as electric charge. These phenomena behave through laws that can be observed in experiments. Although electricity and magnetism have similar effects, their actions are distinct. Understanding how this behaves in the form of interaction, even without prior knowledge of the fundamental origin of the electric charge, is enough for its actions to be applied.This chapter deals with the basics of electricity, magnetism, and electromagnetic induction. We have been decided to start this study presenting the laws that establish the behavior of electrical charges in conductors, i.e. electricity, due to the transport of electrical charges presents its practicality in electrical circuits. In this way, the electric and magnetic link is simpler to be understood. This consideration is generally accepted because electromagnetic induction has the narrow end of its effect acting on some conductor. From this, the wave characteristics of this relationship will be deduced.The division of this Chapter is being shown in the conceptual map of Figure 2.1. It must be made clear, however, that the path chosen is not self-sufficient and definitive as something to be memorized. For those who already have some affinity for circuit theory, note that this is one of several ways to map all this content and one might well not agree. This proposal is intended to approach a very close theory to experiment.Figure 2.1 – Conceptual map of the basic laws of electricity and electromagnetic induction.2.1 ELECTRICITY
The study that deals with purely electrical phenomena is called electricity. These phenomena are generated as a result of the interaction of charges contained in atoms. Electricity arises in matter when the count of the number of electrons that make up its atomic structure becomes unbalanced relative to its number of protons contained in the nucleus. Under equilibrium, any material is electrically neutral. In this way, matter is electrified by either an excess or deficiency of electrons in its elemental structure. This is because there is no change in the number of positive charges reserved for protons in simple electrification processes. This modification happens due to spontaneous emission of radioactive decay or by nuclear reaction processes, as these elements are strongly linked to the forces called nuclear force. Thus, when matter becomes electrified, this behavior can be shown in two ways: one with a manifestation of attraction in relation to another electrified material, and another in the form of a repulsion. However, in relation to discharged matter, the two ways of behaving are the same.
eBook - PDF- James Shipman, Jerry Wilson, Charles Higgins, Bo Lou, James Shipman(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
An illustration of an electromagnetic wave is shown in ●●Fig. 8.24. The wave is trav- eling in the x direction. The electric (E) and magnetic (B) field vectors are at angles of 90° to each other. Accelerated, oscillating charged particles produce electromagnetic waves of various frequencies or wavelengths. These waves form an electromagnetic spec- trum, as discussed in Chapter 6.3. Electromagnetism is one of the most important aspects of physical science, and most of our current technology is directly related to this crucial interaction. Two basic prin- ciples of this interaction are as follows: 1. Moving electric charges (current) give rise to magnetic fields. 2. A magnetic field may deflect a moving electric charge. The first principle forms the basis of an electromagnet considered previously. Electromagnets are found in a variety of applications, such as doorbells, telephones, and devices used to move magnetic materials (see Fig. 8.20). Magnetic Force on Moving Electric Charge The second of the electromagnetic principles may be described in a qualitative way: A magnetic field can be used to deflect moving electric charges. A stationary electric charge in a magnetic field experiences no force, but when a moving charge enters a magnetic field as shown in ●● Fig. 8.25, it experiences a force. This magnetic force (F mag ) is perpendicular to the plane formed by the velocity vector (v) and the magnetic field (B). In the figure, the force initially would be out of the page, and with an extended field, the negatively charged particle would follow a circular arc path. If the moving charge were positive, then it would be deflected in the opposite direction, or into the page. Also, if a charge, positive or negative, is moving parallel to a magnetic field, there is no force on the charge. This effect can be demonstrated experimentally, as shown in ●● Fig.
eBook - PDF- Richard L. Myers(Author)
- 2005(Publication Date)
- Greenwood(Publisher)
Magnetism and Electromagnetism Introduction Magnets have fascinated us since we were young children and provided some of our earliest scientific experiences. These include observations that magnets are attracted to and stick to some metal objects, magnets don't stick to nonmetals, and two magnets might attract or repel each other depending how they are aligned to each other. As early as 600 B.C.E. ancient Greeks recorded simi- lar observations on a type of iron ore called loadstone. A geographic area associated with loadstone was on the Turkish coast near the settlement of Magnesia, thus providing the source of the name used today for mag- netic phenomenon. Magnetic compasses, fashioned out of natural magnetic materials such as lodestone, appeared in China around 800 C.E. William Gilbert (1540-1603), a physician in Queen Elizabeth's court, com- pleted a major work on magnetism in 1600. Gilbert's work, entitled De Magnete, pre- sented two decades of his studies on magne- tism. De Magnete was thefirstcomprehensive scientific examination of magnetism. It dis- cussed aspects such as permanent magnetism, magnetic induction, the loss of magnetism upon heating, and magnetic poles. Gilbert adopted the term "electrick," from the Greek word elektron (elektron was a type of pine pitch or amber that attracted objects when rubbed with various substances), to explain the attractive and repulsive forces associated with charging by friction. Gilbert also pro- posed that the Earth itself was a giant magnet and introduced the idea of magnetic inclina- tion or dip angle. Gilbert was a proponent of Copernicus' heliocentric model, and his ideas were very influential on other scien- tists. He was highly praised by Galileo and is often called the father of modern electric- ity and magnetism. Until the start of the nineteenth cen- tury, magnetism was considered a distinct force separate from electricity.
eBook - PDFElectromagnetism for Engineers
An Introductory Course
- P. Hammond(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
Chapter 6 Electromagnetic Induction 6.1 THE MOTION OF ELECTRIC CHARGES THROUGH MAGNETIC FIELDS In the last chapter we began to investigate the relationship between electricity and magnetism and we saw that magnets and currents produce forces on one another. As a result of our discussion we now know a great deal about the relationship between magnets and currents, but this knowledge is still incomplete, because so far we have not discussed the motion of magnets or currents, nor have we allowed the currents to vary in strength. Moreover the last chapter has been unsatisfactory inasmuch as we have said much about forces on currents, but nothing about forces on electric charges, although it is the object of this book to deal with the statics and dynamics of electric charge. In fact the last chapter was really a digression which was needed to introduce the reader to the idea of the magnetic field and to the various terms which are used in the description and analysis of magnetic fields. In this chapter we return to the main stream of the argument. First of all we must reinterpret the force exerted on a current in a steady magnetic field in terms of the force on a moving charge. Figure 6.1 shows a succession of electric charges Q spaced at a distance δΐ moving with steady velocity v. The current is the rate of passage of 103 104 Electromagnetism for Engineers Q Q Q Q Q Q δΐ F IG. 6.1 Equivalence of moving charges and current charge, so that we can write and since δΙ = νδί (6.2) Ov We can now regard the average current / over a length δΐ as being due to the motion of a single charge Q and we can use eqn. (6.3) to state the equivalence m = Qv (6.4) which means that a current element is equivalent to a charge multiplied by its velocity.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
550 Chapter 22 | Electromagnetic Induction 22.1 | Induced Emf and Induced Current There are a number of ways a magnetic field can be used to generate an electric current, and Figure 22.1 illustrates one of them. This drawing shows a bar magnet and a helical coil of wire to which an ammeter is connected. When there is no relative motion between the magnet and the coil, as in part a of the drawing, the ammeter reads zero, indicating that no current exists. However, when the magnet moves toward the coil, as in part b, a current I appears. As the magnet approaches, the magnetic field B B that it creates at the location of the coil becomes stronger and stronger, and it is this changing field that produces the current. When the magnet moves away from the coil, as in part c, a current is also pro- duced, but with a reversed direction. Now the magnetic field at the coil becomes weaker as the magnet moves away. Once again it is the changing field that generates the current. A current would also be created in Figure 22.1 if the magnet were held stationary and the coil were moved, because the magnetic field at the coil would be changing as the coil approached or receded from the magnet. Only relative motion between the magnet and the coil is needed to generate a current; it does not matter which one moves. The current in the coil is called an induced current because it is brought about (or “in- duced”) by a changing magnetic field. Since a source of emf (electromotive force) is always needed to produce a current, the coil itself behaves as if it were a source of emf. This emf is known as an induced emf. Thus, a changing magnetic field induces an emf in the coil, and the emf leads to an induced current. 22 | Electromagnetic Induction © Jeff Greenberg/Age Fotostock Electric guitars are famous for their amplified and manipulatable sound. To produce this sound, virtually all of them have one or more electro- magnetic pickups located beneath the strings (see Section 22.6).
eBook - PDF- John Kimball(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
Magnetic fields exert forces on moving charges. 2. Moving charges produce magnetic fields. 3. Magnets are almost the same as moving charges, so mag-netic fields exert forces on magnets and magnets produce magnetic fields. 4.4.1 Basic Example Two charges ( q and Q ) provide the simplest example for the compari-son of electricity and magnetism. When these charges are not moving, their mutual repulsion (or attraction) is described by electrostatics and Coulomb’s law ( = / 2 F KQq r ). When both charges are moving, there is an additional magnetic force. The mechanism is shown in Figure 4.15. Because motion is fundamental to magnetism, it no longer suffices to picture charges as little spheres with plus or minus signs. Instead, a suggestive portrayal of magnetic effects imagines charges to be tiny screw-like (helical) objects with their orientations determined by the direction of their motion. Visualize a charge (helical shape) as embedded in a fluid. The motion of a helix through the fluid produces Velocity Velocity Force B B B B B Figure 4.15 The moving charge at the lower left creates a circulating magnetic field. The second charge moving through this field is attracted toward the first charge. 126 PHYSICS CURIOSITIES, ODDITIES, AND NOVELTIES circular stirring. The flow associated with the stirring is the magnetic field, denoted arrowrightnosp B . If a second charge moves in this magnetic field, the flow from the first charge pushes sideways on the moving fins of the second charge. The cross with B in Figure 4.15 means the field is oriented into the page on the fins. The sideways force of attraction on the second moving charge is analogous to lift on an airplane or bird’s wing. The second charge also produces a magnetic field (not shown to keep things simpler) that exerts the equal but oppositely directed attracting force on the first charge. The geometry is complicated, but the result is simple.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler, Heath Jones, Matthew Collins, John Daicopoulos, Boris Blankleider(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
CHAPTER 22 Electromagnetic induction LEARNING OBJECTIVES After reading this module, you should be able to: 22.1 predict when an induced current will flow 22.2 solve motional emf problems 22.3 calculate magnetic flux 22.4 solve problems using Faraday’s law of induction 22.5 predict the direction of an induced current using Lenz’s law 22.6 describe how sound is reproduced via induction 22.7 solve problems involving generators 22.8 define mutual induction and self‐inductance 22.9 solve problems involving transformers. INTRODUCTION Electric guitars are famous for their amplified and manipulatable sound. To produce this sound, virtually all of them have one or more electromagnetic pickups located beneath the strings (see section 22.6). These pickups work because of electromagnetic induction, which is the process by which a magnet is used to create or induce an emf in a coil of wire. In this photograph the pickup is indicated by the shiny rectangle in the white area 22.1 Induced emf and induced current LEARNING OBJECTIVE 22.1 Predict when an induced current will flow. There are a number of ways a magnetic field can be used to generate an electric current, and figure 22.1 illustrates one of them. This drawing shows a bar magnet and a helical coil of wire to which an ammeter is connected. When there is no relative motion between the magnet and the coil, as in part a of the drawing, the ammeter reads zero, indicating that no current exists. However, when the magnet moves towards the coil, as in part b, a current I appears. As the magnet approaches, the magnetic field B that it creates at the location of the coil becomes stronger and stronger, and it is this changing field that produces the current. When the magnet moves away from the coil, as in part c, a current is also produced, but with a reversed direction. Now the magnetic field at the coil becomes weaker as the magnet moves away. Once again it is the changing field that generates the current.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
LEARNING OBJECTIVES After reading this module, you should be able to... 22.1 Predict when an induced current will flow. 22.2 Solve motional emf problems. 22.3 Calculate magnetic flux. 22.4 Solve problems using Faraday’s law of induction. 22.5 Predict the direction of an induced current using Lenz’s law. 22.6 Describe how sound is reproduced via induction. 22.7 Solve problems involving generators. 22.8 Define mutual induction and self- inductance. 22.9 Solve problems involving transformers. © Jeff Greenberg/Age Fotostock CHAPTER 22 Electromagnetic Induction Electric guitars are famous for their amplified and manipulatable sound. To produce this sound, virtually all of them have one or more electromagnetic pickups located beneath the strings (see Section 22.6). These pickups work because of electromagnetic induction, which is the process by which a magnet is used to create or induce an emf in a coil of wire. In this photograph the pickup is indicated by the shiny rectangle in the white area. 22.1 Induced Emf and Induced Current There are a number of ways a magnetic field can be used to generate an electric cur- rent, and Interactive Figure 22.1 illustrates one of them. This drawing shows a bar magnet and a helical coil of wire to which an ammeter is connected. When there is no relative motion between the magnet and the coil, as in part a of the drawing, the ammeter reads zero, indicating that no current exists. However, when the magnet moves toward the coil, as in part b, a current I appears. As the magnet approaches, the magnetic field B → that it creates at the location of the coil becomes stronger and stron- ger, and it is this changing field that produces the current. When the magnet moves away from the coil, as in part c, a current is also produced, but with a reversed direc- tion. Now the magnetic field at the coil becomes weaker as the magnet moves away. Once again it is the changing field that generates the current.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
22.1 | Induced Emf and Induced Current There are a number of ways a magnetic field can be used to generate an electric current, and Figure 22.1 illustrates one of them. This drawing shows a bar magnet and a helical coil of wire to which an ammeter is connected. When there is no relative motion between the magnet and the coil, as in part a of the drawing, the ammeter reads zero, indicating that no current exists. However, when the magnet moves toward the coil, as in part b, a current I appears. As the magnet approaches, the magnetic field B B that it creates at the location of the coil becomes stronger and stronger, and it is this changing field that produces the current. When the magnet moves away from the coil, as in part c, a current is also pro- duced, but with a reversed direction. Now the magnetic field at the coil becomes weaker as the magnet moves away. Once again it is the changing field that generates the current. A current would also be created in Figure 22.1 if the magnet were held stationary and the coil were moved, because the magnetic field at the coil would be changing as the coil approached or receded from the magnet. Only relative motion between the magnet and the coil is needed to generate a current; it does not matter which one moves. The current in the coil is called an induced current because it is brought about (or “in- duced”) by a changing magnetic field. Since a source of emf (electromotive force) is always needed to produce a current, the coil itself behaves as if it were a source of emf. This emf is known as an induced emf. Thus, a changing magnetic field induces an emf in the coil, and the emf leads to an induced current. Electric guitars are famous for their amplified and manipulatable sound. To produce this sound, virtually all of them have one or more electro- magnetic pickups located beneath the strings (see Section 22.6).
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
This drawing shows a bar magnet and a helical coil of wire to which an ammeter is connected. When there is no relative motion between the magnet and the coil, as in part a of the drawing, the ammeter reads zero, indicating that no current exists. However, when the magnet moves toward the coil, as in part b, a current I appears. As the magnet approaches, the magnetic field → B that it creates at the location of the coil becomes stronger and stronger, and it is this changing field that produces the current. When the magnet moves away from the coil, as in part c, a 694 CHAPTER 22 Electromagnetic Induction current is also produced, but with a reversed direction. Now the magnetic field at the coil becomes weaker as the magnet moves away. Once again it is the changing field that generates the current. A current would also be created in Interactive Figure 22.1 if the magnet were held stationary and the coil were moved, because the magnetic field at the coil would be changing as the coil approached or receded from the magnet. Only relative motion between the magnet and the coil is needed to generate a current; it does not matter which one moves. The current in the coil is called an induced current because it is brought about (or “induced”) by a changing magnetic field. Since a source of emf (electromotive force) is always needed to produce a current, the coil itself behaves as if it were a source of emf. This emf is known as an induced emf. Thus, a changing magnetic field induces an emf in the coil, and the emf leads to an induced current. THE PHYSICS OF . . . an automobile cruise control. Induced emf and induced current are frequently used in the cruise controls found in many cars. Interactive Figure 22.2 illustrates how a cruise control operates. Usually two magnets are mounted on opposite sides of the vehicle’s drive shaft, with a stationary sensing coil positioned nearby.
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