Physics
Magnetic Forces and Fields
Magnetic forces and fields refer to the interactions and properties associated with magnets and magnetic materials. These forces are responsible for the attraction or repulsion between magnetic objects and are described by the magnetic field, which is a region where magnetic forces are exerted. Understanding magnetic forces and fields is crucial for various applications, including electromagnetism and magnetic storage technologies.
Written by Perlego with AI-assistance
Related key terms
1 of 5
12 Key excerpts on "Magnetic Forces and Fields"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
An electric field is a field created by an electric charge and such fields are intimately related to magnetic fields; a changing magnetic field genera tes an electric field and a changing electric field produces a magnetic field. The full relationship between the electric and magnetic fields, and the currents and charges that create them, is described by the set of Maxwell's equations. In view of special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic field. A pure electric field in one reference frame is observed as a combination of both an electric field and a magnetic field in a movin g reference frame. In quantum physics, this elec -tromagnetic field is understood to be caused by virtual photons. Most often this quantum description is not needed because the simpler classical theory is sufficient. ________________________ WORLD TECHNOLOGIES ________________________ Magnetic fields have had many uses in an cient and modern society. The Earth produces its own magnetic field, which is important in navigation since the north pole of a compass points toward the south pole of Earth's magnetic field, located near the Earth's geographical north. Rotating magnetic fields are utilized in both electric motors and generators. Magnetic forces give information about the charge carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the disci pline of magnetic circuits. History One of the first drawings of a magnetic field, by René Descartes, 1644. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, threaded parts, through threaded pores in magnets. Although magnets and magnetism were known much earlier, one of the first descriptions of the magnetic field was produced in 1269 C.E.
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... 21.1 Define magnetic field. 21.2 Calculate the magnetic force on a moving charge in a magnetic field. 21.3 Analyze the motion of a charged particle in a magnetic field. 21.4 Describe how the masses of ions are determined using a mass spectrometer. 21.5 Calculate the magnetic force on a current in a magnetic field. 21.6 Calculate the torque on a current- carrying coil. 21.7 Calculate magnetic fields produced by currents. 21.8 Apply Ampère’s law to calculate the magnetic field due to a steady current. 21.9 Describe magnetic materials. Suranga Weeratunga/123RF. com CHAPTER 21 Magnetic Forces and Magnetic Fields This beautiful display of light in the sky is known as the northern lights (aurora borealis). It occurs when charged particles, streaming from the sun, become trapped by the earth’s magnetic field. The particles collide with molecules in the upper atmosphere, and the result is the production of light. Magnetic forces and magnetic fields are the subjects of this chapter. 21.1 Magnetic Fields Permanent magnets have long been used in navigational compasses. As Figure 21.1 illustrates, the compass needle is a permanent magnet supported so it can rotate freely in a plane. When the compass is placed on a horizontal surface, the needle rotates until one end points approximately to the north. The end of the needle that points north is labeled the north magnetic pole; the opposite end is the south magnetic pole. Magnets can exert forces on each other. Figure 21.2 shows that the magnetic forces between north and south poles have the property that like poles repel each other, and unlike poles attract. This behavior is similar to that of like and unlike electric charges. However, there is a significant difference between magnetic poles and electric charges. It is possible to separate positive from negative electric charges and produce isolated charges of either kind.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 9 Magnetic Field A magnetic field is a field of force produced by a magnetic object or particle, or by a changing electric field and is detected by the force it exerts on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. The complex mathematics underlying the magnetic field of an object is usually illustrated using magnetic field lines. These lines are strictly a mathematical concept and do not exist physically. Nonetheless, certain physical phenomena, such as the alignment of iron filings in a magnetic field, produces lines in a similar pattern to the imaginary magnetic field lines of the object. Magnets exert forces and torques on each other through the magnetic fields they create. Electric currents and moving electric charges produce magnetic fields. Even the magnetic field of a magnetic material can be modeled as being due to moving electric charges. Magnetic fields also exert forces on moving electric charges. The magnetic fields within and due to magnetic materials can be quite complicated and is described using two separate fields which can be both called a magnetic field : a magnetic B field and a magnetic H field. Energy is needed to create a magnetic field. This energy can be reclaimed when the field is destroyed and, therefore, can be considered as being stored in the magnetic field. The value of this energy depends on the values of both B and H . An electric field is a field created by an electric charge and such fields are intimately related to magnetic fields; a changing magnetic field generates an electric field and a changing electric field produces a magnetic field. The full relationship between the electric and magnetic fields, and the currents and charges that create them, is described by the set of Maxwell's equations.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 9 Magnetic Field A magnetic field is a field of force produced by moving electric charges, by electric fields that vary in time, and by the 'intrinsic' magnetic field of elementary particles associated with the spin of the particle. There are two separate but closely related fields to which the name 'magnetic field' can refer: a magnetic B field and a magnetic H field. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. The magnetic field is most commonly defined in terms of the Lorentz force it exerts on moving electric charges. The relationship between the magnetic and electric fields, and the currents and charges that create them, is described by the set of Maxwell's equations. In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic field tensor; the aspect of the electromagnetic field that is seen as a magnetic field is dependent on the reference frame of the observer. In quantum physics, the electromagnetic field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields have had many uses in ancient and modern society. The Earth produces its own magnetic field, which is important in navigation since the north pole of a compass points toward the south pole of Earth's magnetic field, located near the Earth's geographical north. Rotating magnetic fields are utilized in both electric motors and generators. Magnetic forces give information about the charge carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits. ________________________ WORLD TECHNOLOGIES ________________________ History One of the first drawings of a magnetic field, by René Descartes, 1644.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Orange Apple(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 4 Magnetic Field A magnetic field is a field of force produced by moving electric charges, by electric fields that vary in time, and by the 'intrinsic' magnetic field of elementary particles associated with the spin of the particle. There are two separate but closely related fields to which the name 'magnetic field' can refer: a magnetic B field and a magnetic H field. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. The magnetic field is most commonly defined in terms of the Lorentz force it exerts on moving electric charges. The relationship between the magnetic and electric fields, and the currents and charges that create them, is described by the set of Maxwell's equations. In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic field tensor; the aspect of the electromagnetic field that is seen as a magnetic field is dependent on the reference frame of the observer. In quantum physics, the electromagnetic field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields have had many uses in ancient and modern society. The Earth produces its own magnetic field, which is important in navigation since the north pole of a compass points toward the south pole of Earth's magnetic field, located near the Earth's geographical north. Rotating magnetic fields are utilized in both electric motors and generators. Magnetic forces give information about the charge carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits. ________________________ WORLD TECHNOLOGIES ________________________ History One of the first drawings of a magnetic field, by René Descartes, 1644.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
______________________________ WORLD TECHNOLOGIES ______________________________ Chapter- 8 Magnetic Field A magnetic field is a field of force produced by moving electric charges, by electric fields that vary in time, and by the 'intrinsic' magnetic field of elementary particles associated with the spin of the particle. There are two separate but closely related fields to which the name 'magnetic field' can refer: a magnetic B field and a magnetic H field. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. The magnetic field is most commonly defined in terms of the Lorentz force it exerts on moving electric charges. The relationship between the magnetic and electric fields, and the currents and charges that create them, is described by the set of Maxwell's equations. In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic field tensor; the aspect of the electromagnetic field that is seen as a magnetic field is dependent on the reference frame of the observer. In quantum physics, the electromagnetic field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields have had many uses in ancient and modern society. The Earth produces its own magnetic field, which is important in navigation since the north pole of a compass points toward the south pole of Earth's magnetic field, located near the Earth's geographical north. Rotating magnetic fields are utilized in both electric motors and generators. Magnetic forces give information about the charge carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits. ______________________________ WORLD TECHNOLOGIES ______________________________ History One of the first drawings of a magnetic field, by René Descartes, 1644.
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 21 Magnetic forces and magnetic fields LEARNING OBJECTIVES After reading this module, you should be able to: 21.1 define magnetic field 21.2 calculate the magnetic force on a moving charge in a magnetic field 21.3 analyse the motion of a charged particle in a magnetic field 21.4 describe how the masses of ions are determined using a mass spectrometer 21.5 calculate the magnetic force on a current in a magnetic field 21.6 calculate the torque on a current‐carrying coil 21.7 calculate magnetic fields produced by currents 21.8 apply Ampère’s law to calculate the magnetic field due to a steady current 21.9 describe magnetic materials. INTRODUCTION This beautiful display of light in the sky is known as the northern lights (aurora borealis). It occurs when charged particles, streaming from the sun, become trapped by the earth’s magnetic field. The particles collide with molecules in the upper atmosphere, and the result is the production of light. Magnetic forces and magnetic fields are the subjects of this chapter. Source: Suranga Weeratunga / 123RF.com 21.1 Magnetic fields LEARNING OBJECTIVE 21.1 Define magnetic field. FIGURE 21.1 The needle of a compass is a permanent magnet that has a north magnetic pole (N) at one end and a south magnetic pole (S) at the other. S N Permanent magnets have long been used in navigational compasses. As figure 21.1 illus- trates, the compass needle is a permanent magnet supported so it can rotate freely in a plane. When the compass is placed on a horizontal surface, the needle rotates until one end points approximately to the north. The end of the needle that points north is labelled the north magnetic pole; the opposite end is the south magnetic pole. Magnets can exert forces on each other. Figure 21.2 shows that the magnetic forces between north and south poles have the property that like poles repel each other, and unlike poles attract. This behaviour is similar to that of like and unlike electric charges.
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
11 | Magnetic Forces and Fields Figure 11.1 An industrial electromagnet is capable of lifting thousands of pounds of metallic waste. (credit: modification of work by “BedfordAl”/Flickr) Chapter Outline 11.1 Magnetism and Its Historical Discoveries 11.2 Magnetic Fields and Lines 11.3 Motion of a Charged Particle in a Magnetic Field 11.4 Magnetic Force on a Current-Carrying Conductor 11.5 Force and Torque on a Current Loop 11.6 The Hall Effect 11.7 Applications of Magnetic Forces and Fields Introduction For the past few chapters, we have been studying electrostatic forces and fields, which are caused by electric charges at rest. These electric fields can move other free charges, such as producing a current in a circuit; however, the electrostatic forces and fields themselves come from other static charges. In this chapter, we see that when an electric charge moves, it generates other forces and fields. These additional forces and fields are what we commonly call magnetism. Before we examine the origins of magnetism, we first describe what it is and how magnetic fields behave. Once we are more familiar with magnetic effects, we can explain how they arise from the behavior of atoms and molecules, and how magnetism is related to electricity. The connection between electricity and magnetism is fascinating from a theoretical point of view, but it is also immensely practical, as shown by an industrial electromagnet that can lift thousands of pounds of metal. Chapter 11 | Magnetic Forces and Fields 493 11.1 | Magnetism and Its Historical Discoveries Learning Objectives By the end of this section, you will be able to: • Explain attraction and repulsion by magnets • Describe the historical and contemporary applications of magnetism Magnetism has been known since the time of the ancient Greeks, but it has always been a bit mysterious.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
653 Active regions on the surface of the sun correspond to areas of intense magnetic fields. The looping magnetic field lines above this area are illuminated by the motion of charged particles. The moving charges experience a force in the magnetic field and spiral along them. In this chapter, we will study magnetic fields and the forces they apply to charged particles. The sizes of these magnetic structures can be enormous, as the earth, drawn to scale at the lower right, demonstrates. LEARNING OBJECTIVES After reading this module, you should be able to... 21.1 Define magnetic field. 21.2 Calculate the magnetic force on a moving charge in a magnetic field. 21.3 Analyze the motion of a charged particle in a magnetic field. 21.4 Describe how the masses of ions are determined using a mass spectrometer. 21.5 Calculate the magnetic force on a current in a magnetic field. 21.6 Calculate the torque on a current-carrying coil. 21.7 Calculate magnetic fields produced by currents. 21.8 Apply Ampère’s law to calculate the magnetic field due to a steady current. 21.9 Describe magnetic materials. Magnetic Forces and Magnetic Fields CHAPTER 21 21.1 Magnetic Fields Permanent magnets have long been used in navigational compasses. As Figure 21.1 illustrates, the compass needle is a permanent magnet sup- ported so it can rotate freely in a plane. When the compass is placed on a horizontal surface, the needle rotates until one end points approximately to the north. The end of the needle that points north is labeled the north magnetic pole; the opposite end is the south magnetic pole. Magnets can exert forces on each other. Figure 21.2 shows that the magnetic forces between north and south poles have the property that like poles repel each other, and unlike poles attract. This behavior is similar to that of like and unlike electric charges. How- ever, there is a significant difference between magnetic poles and electric charges.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
Like the electric field, the magnetic field has both a magnitude and a direction. We postpone a dis- cussion of the magnitude until Section 21.2, concentrating our attention here on the Chapter | 21 LEARNING OBJECTIVES After reading this module, you should be able to... 21.1 | Define magnetic field. 21.2 | Calculate the magnetic force on a moving charge in a magnetic field. 21.3 | Analyze the motion of a charged particle in a magnetic field. 21.4 | Describe how the masses of ions are determined using a mass spectrometer. 21.5 | Calculate the magnetic force on a current in a magnetic field. 21.6 | Calculate the torque on a current- carrying coil. 21.7 | Calculate magnetic fields produced by currents. 21.8 | Apply Ampère’s law to calculate the magnetic field due to a steady current. 21.9 | Describe magnetic materials. 580 Suranga Weeratunga/123RF. com S N Figure 21.1 The needle of a compass is a permanent magnet that has a north magnetic pole (N) at one end and a south magnetic pole (S) at the other. Like poles repel (a) Unlike poles attract (b) Figure 21.2 Bar magnets have a north magnetic pole at one end and a south magnetic pole at the other end. (a) Like poles repel each other, and (b) unlike poles attract. 21.1 | Magnetic Fields 581 direction. The direction of the magnetic field at any point in space is the direction indicated by the north pole of a small compass needle placed at that point. In Fig- ure 21.3 the compass needle is symbolized by an arrow, with the head of the arrow representing the north pole. The drawing shows how compasses can be used to map out the magnetic field in the space around a bar magnet. Since like poles repel and unlike poles attract, the needle of each compass becomes aligned relative to the magnet in the manner shown in the picture. The compass needles provide a visual picture of the magnetic field that the bar magnet creates. To help visualize the electric field, we introduced electric field lines in Section 18.7.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
Like the electric field, the magnetic field has both a magnitude and a direction. We postpone a dis- cussion of the magnitude until Section 21.2, concentrating our attention here on the Chapter | 21 LEARNING OBJECTIVES After reading this module, you should be able to... 21.1 | Define magnetic field. 21.2 | Calculate the magnetic force on a moving charge in a magnetic field. 21.3 | Analyze the motion of a charged particle in a magnetic field. 21.4 | Describe how the masses of ions are determined using a mass spectrometer. 21.5 | Calculate the magnetic force on a current in a magnetic field. 21.6 | Calculate the torque on a current- carrying coil. 21.7 | Calculate magnetic fields produced by currents. 21.8 | Apply Ampère’s law to calculate the magnetic field due to a steady current. 21.9 | Describe magnetic materials. 518 Suranga Weeratunga/123RF. com S N Figure 21.1 The needle of a compass is a permanent magnet that has a north magnetic pole (N) at one end and a south magnetic pole (S) at the other. Like poles repel (a) Unlike poles attract (b) Figure 21.2 Bar magnets have a north magnetic pole at one end and a south magnetic pole at the other end. (a) Like poles repel each other, and (b) unlike poles attract. 21.1 | Magnetic Fields 519 direction. The direction of the magnetic field at any point in space is the direction indicated by the north pole of a small compass needle placed at that point. In Fig- ure 21.3 the compass needle is symbolized by an arrow, with the head of the arrow representing the north pole. The drawing shows how compasses can be used to map out the magnetic field in the space around a bar magnet. Since like poles repel and unlike poles attract, the needle of each compass becomes aligned relative to the magnet in the manner shown in the picture. The compass needles provide a visual picture of the magnetic field that the bar magnet creates. To help visualize the electric field, we introduced electric field lines in Section 18.7.
eBook - PDF- Michael Tammaro(Author)
- 2019(Publication Date)
- Wiley(Publisher)
The science of magnetism is extremely old, with the earliest reference to permanent magnets dating from the 4th century BCE. Permanent magnets produce magnetic fields, which exert forces and torques on other permanent magnets. The photo shows a ferrofluid that sits on a horizontal piece of glass, which is balanced on a strong permanent magnet (not seen). A ferrofluid is an oily liquid in which a large number of small ferromagnetic particles are suspended. In the presence of a magnetic field, these particles behave like tiny bar magnets. When a ferrofluid is influenced by a strong magnet, it can morph into a variety of complex shapes like the one shown here. SPL/Science Source Images Magnetic Forces and Magnetic Fields 21 572 Magnetic Fields | 573 21.1 Interpret the magnetic field lines that surround bar magnets and the Earth. An electric charge creates an electric field in the space surrounding it. In a similar manner, a permanent magnet creates a magnetic field in the space surrounding it. Electric currents produce magnetic fields, too, but we begin our study of magnetism with some observations about the magnetic field produced by a permanent magnet. Permanent Magnets The basic unit of electricity is the electric point charge. The electric field depends on the distance r from the point charge and is directed radially outward or inward (for positive or negative charges, respectively). The basic unit of magnetism, on the other hand, is the magnetic dipole. The magnetic field of a magnetic dipole is more complex than the elec- tric field of a point charge. A magnetic dipole can be thought of as a tiny bar magnet, and the magnetic field it creates is similar to that of the bar magnet in Figure 21.1.1(a). The needle of a small compass—which is itself a small bar magnet—points in the direction of the magnetic field. In Figure 21.1.1(a), a small compass is being used as a test magnet to map out the magnetic field.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
