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Chapter 9

Chapter 9. Magnetism. Objectives. After completing this chapter, you will be able to: Identify three types of magnets Describe the basic shapes of magnets Describe the differences between permanent magnets and temporary magnets Describe how the earth functions as a magnet

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Chapter 9

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  1. Chapter 9 Magnetism

  2. Objectives • After completing this chapter, you will be able to: • Identify three types of magnets • Describe the basic shapes of magnets • Describe the differences between permanent magnets and temporary magnets • Describe how the earth functions as a magnet • State the laws of magnetism

  3. Objectives (cont’d.) • Explain magnetism based on the theory of atoms and electron spin • Explain magnetism based on the domain theory • Identify flux lines and their significance • Define permeability • Describe the magnetic effects of current flowing through a conductor

  4. Objectives (cont’d.) • Describe the principle of an electromagnet • Describe how to determine the polarity of an electro-magnet using the left-hand rule • Define magnetic induction • Define retentivity and residual magnetism • Define a magnetic shield

  5. Objectives (cont’d.) • Describe how magnetism is used to generate electricity • State the basic law of electromagnetism • Describe how the left-hand rule for generators can be used to determine the polarity of induced voltage • Describe how AC and DC generators convert mechanical energy into electrical energy

  6. Objectives (cont’d.) • Describe how a relay operates as an electromechanical switch • Discuss the similarities between a doorbell and a relay • Discuss the similarities between a solenoid and a relay • Describe how a magnetic phonograph cartridge works. • Describe how a loudspeaker operates

  7. Objectives (cont’d.) • Describe how information can be stored and retrieved using magnetic recording • Describe how a DC motor operates

  8. Magnetic Fields • Magnetite • Natural magnet • Artificial magnet • Created by rubbing soft iron with another magnet • Electromagnet • Created by current flowing through a coil of wire

  9. Magnetic Fields (cont’d.) Figure 9-2. The earth’s magnetic north and south poles are situated close to the geographic North and South Poles.

  10. Figure 9-3. The domains in unmagnetized material are randomly arranged with no overall magnetic effect Figure 9-4. When material becomes magnetized, all the domains align in a common direction.

  11. Magnetic Fields (cont’d.) Figure 9-6. Magnetic lines of flux can be seen in patterns of iron filings.

  12. Electricity and Magnetism Figure 9-7. A current flowing through a conductor creates a magnetic field around the conductor.

  13. Figure 9-8. Determining the direction of the flux lines around a conductor when the direction of the current flow is known (left-hand rule for conductors).

  14. Electricity and Magnetism (cont’d.) Figure 9-9. When current flows in opposite directions through two conductors placed next to each other, the resulting magnetic fields repel each other.

  15. Electricity and Magnetism (cont’d.) Figure 9-10. When current flows in the same direction through two conductors placed next to each other, the magnetic fields combine.

  16. Figure 9-11. Determining the polarity of an electromagnet (left-hand rule for coils).

  17. Magnetic Induction Figure 9-12. Placing an iron bar in a magnetic field extends the magnetic field and magnetizes the iron bar.

  18. MOTION FLUX CURRENT Figure 9-13. The left-hand rule for generators can be used to determine the direction of the induced current flow in a generator.

  19. Figure 9-14. Induced voltage in an AC generator.

  20. Figure 9-15. Induced voltage in an DC generator.

  21. Figure 9-18. Operation of a DC motor.

  22. Summary • Electric current always produces some form of magnetism • Magnetism is the most common method for generating electricity • One theory of magnetism is based on the spin of electrons as they orbit around an atom

  23. Summary (cont’d.) • Another theory of magnetism is based on the alignment of domains • A magnetic field surrounds a wire when current flows through it • Left-hand rule: for conductors, coils, and generators • Faraday’s law: the basic law of electromagnetism

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