Halderman ch039 lecture

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  • Figure 39-1 In an atom (left), electrons orbit protons in the nucleus just as planets orbit the sun in our solar system (right).
  • Figure 39-2 The nucleus of an atom has a positive (+) charge and the surrounding electrons have a negative (-) charge.
  • Figure 39-3 This figure shows a balanced atom. The number of electrons is the same as the number of protons in the nucleus.
  • Figure 39-4 Unlike charges attract and like charges repel.
  • Figure 39-5 An unbalanced, positively charged atom (ion) will attract electrons from neighboring atoms.
  • Figure 39-6 The hydrogen atom is the simplest atom, with only one proton, one neutron, and one electron. More complex elements contain higher numbers of protons, neutrons, and electrons.
  • Figure 39-7 As the number of electrons increases, they occupy increasing energy levels that are farther from the center of the atom.
  • Figure 39-8 Electrons in the outer orbit, or shell, can often be drawn away from the atom and become free electrons.
  • Figure 39-9 A conductor is any element that has one to three electrons in its outer orbit.
  • Figure 39-10 Copper is an excellent conductor of electricity because it has just one electron in its outer orbit, making it easy to be knocked out of its orbit and flow to other nearby atoms. This causes electron flow, which is the definition of electricity.
  • Figure 39-11 Insulators are elements with five to eight electrons in the outer orbit.
  • Figure 39-12 Semiconductor elements contain exactly four electrons in the outer orbit.
  • Figure 39-13 Current electricity is the movement of electrons through a conductor.
  • Figure 39-14 Conventional theory states that current flows through a circuit from positive (+) to negative (-). Automotive electricity uses the conventional theory in all electrical diagrams and schematics.
  • Figure 39-15 One ampere is the movement of 1 coulomb (6.28 billion billion electrons) past a point in 1 second.
  • Figure 39-16 An ammeter is installed in the path of the electrons similar to a water meter used to measure the flow of water in gallons per minute. The ammeter displays current flow in amperes.
  • Figure 39-17 Voltage is the electrical pressure that causes the electrons to flow through a conductor.
  • Figure 39-18 This digital multimeter set to read DC volts is being used to test the voltage of a vehicle battery. Most multimeters can also measure resistance (ohms) and current flow (amperes).
  • Figure 39-19 Resistance to the flow of electrons through a conductor is measured in ohms.
  • Figure 39-20 A display at the Henry Ford Museum in Dearborn, Michigan, which includes a hand-cranked generator and a series of light bulbs. This figure shows a young man attempting to light as many bulbs as possible. The crank gets harder to turn as more bulbs light because it requires more power to produce the necessary watts of electricity.
  • Figure 39-21 Electron flow is produced by heating the connection of two different metals.
  • Figure 39-22 Electron flow is produced by light striking a light-sensitive material.
  • Figure 39-23 Electron flow is produced by pressure on certain crystals.
  • Chart 39-1 Conductor ratings (starting with the best).
  • Figure 39-24 This figure shows a resistor color-code interpretation.
  • Figure 39-25 A typical carbon resistor.
  • Figure 39-26 A three-wire variable resistor is called a potentiometer.
  • Figure 39-27 A two-wire variable resistor is called a rheostat.
  • Halderman ch039 lecture

    1. 1. ELECTRICAL FUNDAMENTALS 39
    2. 2. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic System Diagnosis). </li></ul></ul><ul><ul><li>Define electricity. </li></ul></ul><ul><ul><li>Explain the units of electrical measurement. </li></ul></ul>
    3. 3. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Discuss the relationship among volts, amperes, and ohms. </li></ul></ul><ul><ul><li>Explain how magnetism is used in automotive applications. </li></ul></ul>
    4. 4. INTRODUCTION
    5. 5. Introduction <ul><li>Electrical system one of most important in vehicle. </li></ul><ul><li>More and more components and systems use electricity. </li></ul><ul><li>Technicians who understand automotive electronic systems are in demand. </li></ul>
    6. 6. ELECTRICITY
    7. 7. Electricity <ul><li>Background </li></ul><ul><ul><li>Universe composed of matter. </li></ul></ul><ul><ul><li>Matter is anything that has mass and occupies space. </li></ul></ul>
    8. 8. Electricity <ul><li>Background </li></ul><ul><ul><li>All matter made from elements. </li></ul></ul><ul><ul><li>Atom is smallest particle element can be broken into and still retain properties. </li></ul></ul>
    9. 9. Figure 39-1 In an atom (left), electrons orbit protons in the nucleus just as planets orbit the sun in our solar system (right).
    10. 10. Electricity <ul><li>Definition </li></ul><ul><ul><li>Movement of electrons from one atom to another. </li></ul></ul><ul><ul><li>Nucleus: dense center of atom. </li></ul></ul><ul><ul><ul><li>Protons: positive charge. </li></ul></ul></ul><ul><ul><ul><li>Neutrons: electrically neutral (no charge). </li></ul></ul></ul>
    11. 11. Electricity <ul><li>Definition </li></ul><ul><ul><li>Electrons (negative charge) surround nucleus in orbits. </li></ul></ul><ul><ul><li>Each atom has equal number of electrons and protons. </li></ul></ul><ul><ul><li>Number of electrons and protons determines how electricity conducted. </li></ul></ul>
    12. 12. Electricity <ul><li>Positive and Negative Charges </li></ul><ul><ul><li>Protons have positive charge (+). </li></ul></ul><ul><ul><li>Electrons have negative charge (–). </li></ul></ul>
    13. 13. Electricity <ul><li>Positive and Negative Charges </li></ul><ul><ul><li>Neutrons have no charge (neutral). </li></ul></ul><ul><ul><li>+ and – signs also identify parts of electrical circuit. </li></ul></ul>
    14. 14. Figure 39-2 The nucleus of an atom has a positive (+) charge and the surrounding electrons have a negative (-) charge.
    15. 15. Figure 39-3 This figure shows a balanced atom. The number of electrons is the same as the number of protons in the nucleus.
    16. 16. Electricity <ul><li>Magnets and Electrical Charges </li></ul><ul><ul><li>Ordinary magnet has two ends, or poles </li></ul></ul><ul><ul><ul><li>South pole, north pole. </li></ul></ul></ul><ul><ul><ul><li>Like poles repel each other, opposite poles attract. </li></ul></ul></ul>
    17. 17. Electricity <ul><li>Magnets and Electrical Charges </li></ul><ul><ul><li>Positive and negative charges within atom like north and south poles. </li></ul></ul><ul><ul><li>Reason that electrons orbit protons. </li></ul></ul><ul><ul><ul><li>Electrons repel each other, but attracted to protons. </li></ul></ul></ul>
    18. 18. Figure 39-4 Unlike charges attract and like charges repel.
    19. 19. Electricity <ul><li>Ions </li></ul><ul><ul><li>Atom unbalanced when loses electrons—ion. </li></ul></ul><ul><ul><ul><li>Lose electrons—positively charged. </li></ul></ul></ul><ul><ul><ul><li>Gain electrons—negatively charged. </li></ul></ul></ul>
    20. 20. Electricity <ul><li>Ions </li></ul><ul><ul><li>Ions regain balance by exchanging electrons with neighboring atoms. </li></ul></ul><ul><ul><li>Flow of electrons during “equalization” defined as flow of electricity. </li></ul></ul>
    21. 21. Figure 39-5 An unbalanced, positively charged atom (ion) will attract electrons from neighboring atoms.
    22. 22. Electricity <ul><li>Electron Shells </li></ul><ul><ul><li>Electrons orbit nucleus in definite paths. </li></ul></ul><ul><ul><li>Paths form shells, like concentric rings. </li></ul></ul>
    23. 23. Electricity <ul><li>Electron Shells </li></ul><ul><ul><li>Only specific number can orbit within each shell. </li></ul></ul><ul><ul><li>If too many electrons for first shell, others orbit in outer shells. </li></ul></ul><ul><ul><li>Up to 7 shells. </li></ul></ul>
    24. 24. Figure 39-6 The hydrogen atom is the simplest atom, with only one proton, one neutron, and one electron. More complex elements contain higher numbers of protons, neutrons, and electrons.
    25. 25. Electricity <ul><li>Free and Bound Electrons </li></ul><ul><ul><li>Valence ring: outermost and most important ring for electricity. </li></ul></ul><ul><ul><li>Number of electrons in this ring determines valence of atom. </li></ul></ul><ul><ul><li>Valence indicates atom ’s capacity to combine with other atoms. </li></ul></ul>
    26. 26. Electricity <ul><li>Free and Bound Electrons </li></ul><ul><ul><li>If 3 or fewer electrons in ring, room for more. </li></ul></ul><ul><ul><ul><li>Electrons held very loosely (free electrons). </li></ul></ul></ul><ul><ul><ul><li>Easy for drifting electron to join ring. </li></ul></ul></ul>
    27. 27. Electricity <ul><li>Free and Bound Electrons </li></ul><ul><ul><li>If 5 or more electrons in ring, ring fairly full. </li></ul></ul><ul><ul><ul><li>Electrons held tightly (bound electrons). </li></ul></ul></ul><ul><ul><ul><li>Difficult for drifting electron to join ring. </li></ul></ul></ul>
    28. 28. Electricity <ul><li>Free and Bound Electrons </li></ul><ul><ul><li>Current: movement of drifting electrons </li></ul></ul><ul><ul><ul><li>Can be small (few electrons) or large (many electrons). </li></ul></ul></ul><ul><ul><li>Electric current: controlled, directed movement of electrons from atom to atom within conductor. </li></ul></ul>
    29. 29. Figure 39-7 As the number of electrons increases, they occupy increasing energy levels that are farther from the center of the atom.
    30. 30. Figure 39-8 Electrons in the outer orbit, or shell, can often be drawn away from the atom and become free electrons.
    31. 31. Electricity <ul><li>Conductors </li></ul><ul><ul><li>Materials with fewer than 4 electrons in atom ’s outer orbit. </li></ul></ul><ul><ul><li>Copper excellent conductor. </li></ul></ul><ul><ul><ul><li>Only one electron in outer orbit. </li></ul></ul></ul><ul><ul><ul><li>Orbit far enough from nucleus that only weak force holds electron. </li></ul></ul></ul>
    32. 32. Electricity <ul><li>Conductors </li></ul><ul><ul><li>Copper most used conductor in vehicles. </li></ul></ul><ul><ul><ul><li>Price reasonable compared to other materials with same qualities. </li></ul></ul></ul>
    33. 33. Electricity <ul><li>Conductors </li></ul><ul><ul><li>Other commonly used conductors: </li></ul></ul><ul><ul><ul><li>Silver. </li></ul></ul></ul><ul><ul><ul><li>Gold. </li></ul></ul></ul>
    34. 34. Electricity <ul><li>Conductors </li></ul><ul><ul><li>Other commonly used conductors: </li></ul></ul><ul><ul><ul><li>Aluminum. </li></ul></ul></ul><ul><ul><ul><li>Steel. </li></ul></ul></ul><ul><ul><ul><li>Cast iron. </li></ul></ul></ul>?
    35. 35. Figure 39-9 A conductor is any element that has one to three electrons in its outer orbit.
    36. 36. Figure 39-10 Copper is an excellent conductor of electricity because it has just one electron in its outer orbit, making it easy to be knocked out of its orbit and flow to other nearby atoms. This causes electron flow, which is the definition of electricity.
    37. 37. Electricity <ul><li>Insulators </li></ul><ul><ul><li>Materials that hold their electrons very tightly. </li></ul></ul><ul><ul><li>Electrons do not move through them very well. </li></ul></ul>
    38. 38. Electricity <ul><li>Insulators </li></ul><ul><ul><li>Have more than four electrons in outer orbit. </li></ul></ul><ul><ul><li>Easier to acquire electrons than to release electrons. </li></ul></ul>
    39. 39. Electricity <ul><li>Insulators </li></ul><ul><ul><li>Commonly used conductors: </li></ul></ul><ul><ul><ul><li>Rubber. </li></ul></ul></ul><ul><ul><ul><li>Plastic. </li></ul></ul></ul><ul><ul><ul><li>Nylon. </li></ul></ul></ul>
    40. 40. Electricity <ul><li>Insulators </li></ul><ul><ul><li>Commonly used conductors: </li></ul></ul><ul><ul><ul><li>Porcelain. </li></ul></ul></ul><ul><ul><ul><li>Ceramic. </li></ul></ul></ul><ul><ul><ul><li>Fiberglass. </li></ul></ul></ul>
    41. 41. Figure 39-11 Insulators are elements with five to eight electrons in the outer orbit.
    42. 42. Electricity <ul><li>Semiconductors </li></ul><ul><ul><li>Materials with exactly four electrons in outer orbit. </li></ul></ul><ul><ul><li>Can be either insulator or conductor in different applications. </li></ul></ul>
    43. 43. Electricity <ul><li>Semiconductors </li></ul><ul><ul><li>Common semiconductors. </li></ul></ul><ul><ul><ul><li>Silicon. </li></ul></ul></ul><ul><ul><ul><li>Germanium. </li></ul></ul></ul><ul><ul><ul><li>Carbon. </li></ul></ul></ul>
    44. 44. Electricity <ul><li>Semiconductors </li></ul><ul><ul><li>Used mostly in transistors, computers, other electronic devices. </li></ul></ul>
    45. 45. Figure 39-12 Semiconductor elements contain exactly four electrons in the outer orbit.
    46. 46. HOW ELECTRONS MOVE THROUGH A CONDUCTOR
    47. 47. How Electrons Move Through a Conductor <ul><li>Current Flow </li></ul><ul><ul><li>Certain events occur if source of power connected to ends of conductor. </li></ul></ul><ul><ul><ul><li>Positive charge (lack of electrons) on one end. </li></ul></ul></ul><ul><ul><ul><li>Negative charge (excess of electrons) on other end. </li></ul></ul></ul>
    48. 48. How Electrons Move Through a Conductor <ul><li>Current Flow </li></ul><ul><ul><li>Imbalance required for current to flow. </li></ul></ul><ul><ul><ul><li>Negative charge on one end repels free electrons in conductor. </li></ul></ul></ul><ul><ul><ul><li>Positive charge on other end attracts electrons. </li></ul></ul></ul><ul><ul><ul><li>Result is electrons flowing through conductor. </li></ul></ul></ul>
    49. 49. How Electrons Move Through a Conductor <ul><li>Current Flow </li></ul><ul><ul><li>Imbalance required for current to flow. </li></ul></ul><ul><ul><ul><li>Result is electrons flowing through conductor. </li></ul></ul></ul>
    50. 50. Figure 39-13 Current electricity is the movement of electrons through a conductor.
    51. 51. How Electrons Move Through a Conductor <ul><li>Conventional Theory Versus Electron Theory </li></ul><ul><ul><li>Conventional: electricity has one charge; moves from positive to negative. </li></ul></ul><ul><ul><li>Electron: electrons flow from negative to positive. </li></ul></ul><ul><ul><li>Most automotive applications use conventional theory. </li></ul></ul>
    52. 52. Figure 39-14 Conventional theory states that current flows through a circuit from positive (+) to negative (−). Automotive electricity uses the conventional theory in all electrical diagrams and schematics.
    53. 53. UNITS OF ELECTRICITY
    54. 54. Units of Electricity <ul><li>Amperes </li></ul><ul><ul><li>Unit used throughout world to measure current flow. </li></ul></ul><ul><ul><li>Named for French electrician, Andre Marie Ampere (1775–1836). </li></ul></ul><ul><ul><li>1 ampere = 6.28 billion billion electrons (1 coulomb) moving past point in 1 second. </li></ul></ul>
    55. 55. Units of Electricity <ul><li>Amperes </li></ul><ul><ul><li>A and amps are acceptable abbreviations for amperes. </li></ul></ul><ul><ul><li>Capital letter I (intensity) used in math to represent amperes. </li></ul></ul>
    56. 56. Units of Electricity <ul><li>Amperes </li></ul><ul><ul><li>Amperes do the actual work in circuit. </li></ul></ul><ul><ul><ul><li>Without amperage, device will not work. </li></ul></ul></ul><ul><ul><li>Measured by ammeter. </li></ul></ul>
    57. 57. Figure 39-15 One ampere is the movement of 1 coulomb (6.28 billion billion electrons) past a point in 1 second.
    58. 58. Figure 39-16 An ammeter is installed in the path of the electrons similar to a water meter used to measure the flow of water in gallons per minute. The ammeter displays current flow in amperes.
    59. 59. Units of Electricity <ul><li>Volts </li></ul><ul><ul><li>Unit of measurement for electrical pressure. </li></ul></ul><ul><ul><li>Named for Italian physicist, Alessandro Volta (1745–1827). </li></ul></ul>
    60. 60. Units of Electricity <ul><li>Volts </li></ul><ul><ul><li>Comparable to psi (pounds per square inch). </li></ul></ul><ul><ul><li>Possible to have very high pressures (volts) and low flow (amperes). </li></ul></ul>
    61. 61. Units of Electricity <ul><li>Volts </li></ul><ul><ul><li>Possible to have high flow (amperes) and low pressures (volts). </li></ul></ul><ul><ul><li>Also called electrical potential. </li></ul></ul><ul><ul><ul><li>If voltage present in conductor, potential for current flow. </li></ul></ul></ul>
    62. 62. Units of Electricity <ul><li>Volts </li></ul><ul><ul><li>Voltage causes current (in amperes) to flow through conductors. </li></ul></ul><ul><ul><li>Electromotive force (EMF) another way of indicating voltage. </li></ul></ul>
    63. 63. Units of Electricity <ul><li>Volts </li></ul><ul><ul><li>V generally accepted abbreviation for volts. </li></ul></ul><ul><ul><li>Symbol used in calculations is E, for electromotive force. </li></ul></ul><ul><ul><li>Measured by voltmeter. </li></ul></ul>
    64. 64. Figure 39-17 Voltage is the electrical pressure that causes the electrons to flow through a conductor.
    65. 65. Figure 39-18 This digital multimeter set to read DC volts is being used to test the voltage of a vehicle battery. Most multimeters can also measure resistance (ohms) and current flow (amperes).
    66. 66. Units of Electricity <ul><li>Ohms </li></ul><ul><ul><li>Resistance to the flow of current through a conductor. </li></ul></ul><ul><ul><li>Named after German physicist, George Simon Ohm (1787–1854). </li></ul></ul>
    67. 67. Units of Electricity <ul><li>Ohms </li></ul><ul><ul><li>Results from collisions electrons cause within atoms of conductor. </li></ul></ul><ul><ul><li>Unit of measurement for electrical resistance. </li></ul></ul>
    68. 68. Units of Electricity <ul><li>Ohms </li></ul><ul><ul><li>Symbol is Ω (Greek capital letter omega). </li></ul></ul><ul><ul><li>Symbol in calculations is R , for resistance. </li></ul></ul>
    69. 69. Units of Electricity <ul><li>Ohms </li></ul><ul><ul><li>Measured by an ohmmeter. </li></ul></ul><ul><ul><li>Resistance depends on material used as conductor. </li></ul></ul>
    70. 70. Figure 39-19 Resistance to the flow of electrons through a conductor is measured in ohms.
    71. 71. Units of Electricity <ul><li>Watts </li></ul><ul><ul><li>Electrical unit for power, or capacity to do work. </li></ul></ul><ul><ul><li>Symbol is P. </li></ul></ul><ul><ul><li>Calculated as amperes times volts: </li></ul></ul><ul><ul><li>P = I × E. </li></ul></ul>
    72. 72. Figure 39-20 A display at the Henry Ford Museum in Dearborn, Michigan, which includes a hand-cranked generator and a series of light bulbs. This figure shows a young man attempting to light as many bulbs as possible. The crank gets harder to turn as more bulbs light because it requires more power to produce the necessary watts of electricity.
    73. 73. SOURCES OF ELECTRICITY
    74. 74. Sources of Electricity <ul><li>Friction </li></ul><ul><ul><li>Certain different materials rubbed together, become electrically charged. </li></ul></ul><ul><ul><li>Charges not in motion, but stay on surface where deposited. </li></ul></ul>
    75. 75. Sources of Electricity <ul><li>Friction </li></ul><ul><ul><li>Called static electricity. </li></ul></ul><ul><ul><li>Vehicle tires rolling on pavement often create static electricity. </li></ul></ul>
    76. 76. Sources of Electricity <ul><li>Heat </li></ul><ul><ul><li>Two different metals joined at both ends. </li></ul></ul><ul><ul><li>If one junction heated, current passes through metals. </li></ul></ul>
    77. 77. Sources of Electricity <ul><li>Heat </li></ul><ul><ul><li>Current very small (millionths of an ampere). </li></ul></ul><ul><ul><li>Enough current to use in a thermocouple. </li></ul></ul><ul><ul><li>Called thermoelectricity. </li></ul></ul>
    78. 78. Sources of Electricity <ul><li>Heat </li></ul><ul><ul><li>Used in some engine temperature sensors. </li></ul></ul><ul><ul><li>Peltier effect: electrons moving through solid can carry heat from one side to the other. </li></ul></ul>
    79. 79. Figure 39-21 Electron flow is produced by heating the connection of two different metals.
    80. 80. Sources of Electricity <ul><li>Light </li></ul><ul><ul><li>Some of light energy is transferred to free electrons in metal. </li></ul></ul><ul><ul><li>Breaks electrons loose from surface of metal. </li></ul></ul>
    81. 81. Sources of Electricity <ul><li>Light </li></ul><ul><ul><li>Electrons can be made to flow through conductor. </li></ul></ul><ul><ul><li>Called photoelectricity. </li></ul></ul><ul><ul><li>Used in light-measuring devices such as automatic headlamp dimmers. </li></ul></ul>
    82. 82. Figure 39-22 Electron flow is produced by light striking a light-sensitive material.
    83. 83. Sources of Electricity <ul><li>Pressure </li></ul><ul><ul><li>First explained in 1880 by Pierre and Jacques Curie. </li></ul></ul><ul><ul><li>Called piezoelectricity. </li></ul></ul><ul><ul><li>Used by engine knock sensor to create voltage signal for engine computer. </li></ul></ul>
    84. 84. Figure 39-23 Electron flow is produced by pressure on certain crystals.
    85. 85. Sources of Electricity <ul><li>Chemical </li></ul><ul><ul><li>Two different materials placed in conducting, reactive chemical solution. </li></ul></ul><ul><ul><li>Create a difference in potential, or voltage. </li></ul></ul>
    86. 86. Sources of Electricity <ul><li>Chemical </li></ul><ul><ul><li>Called electrochemistry. </li></ul></ul><ul><ul><li>Basis of the automotive battery. </li></ul></ul>
    87. 87. Sources of Electricity <ul><li>Magnetism </li></ul><ul><ul><li>Electricity produced if conductor moved through magnetic field. </li></ul></ul><ul><ul><li>Also produced if moving magnetic field moved near conductor. </li></ul></ul>
    88. 88. Sources of Electricity <ul><li>Magnetism </li></ul><ul><ul><li>Used in many automotive devices. </li></ul></ul><ul><ul><ul><li>Starter motor. </li></ul></ul></ul><ul><ul><ul><li>Alternator. </li></ul></ul></ul>
    89. 89. Sources of Electricity <ul><li>Magnetism </li></ul><ul><ul><li>Used in many automotive devices. </li></ul></ul><ul><ul><ul><li>Ignition coils. </li></ul></ul></ul><ul><ul><ul><li>Solenoids and relays. </li></ul></ul></ul>
    90. 90. CONDUCTORS AND RESISTANCE
    91. 91. Conductors and Resistance <ul><li>All conductors have some resistance to current flow. </li></ul><ul><li>If conductor length is doubled, resistance doubles. </li></ul>
    92. 92. Conductors and Resistance <ul><li>If conductor diameter is increased, resistance is reduced. </li></ul><ul><li>As temperature increases, resistance of conductor also increases. </li></ul><ul><li>Materials used in conductor have impact on its resistance. </li></ul>?
    93. 93. Chart 39-1 Conductor ratings (starting with the best).
    94. 94. RESISTORS
    95. 95. Resistors <ul><li>Fixed Resistors </li></ul><ul><ul><li>Resistors represent electrical load, or resistance, to current flow. </li></ul></ul><ul><ul><li>Resistors used to limit and control flow of current. </li></ul></ul>
    96. 96. Resistors <ul><li>Fixed Resistors </li></ul><ul><ul><li>Can be made from carbon or other materials that restrict flow. </li></ul></ul><ul><ul><li>Available in various sizes and resistance values. </li></ul></ul>
    97. 97. Resistors <ul><li>Fixed Resistors </li></ul><ul><ul><li>Most have series of painted color bands. </li></ul></ul><ul><ul><li>Color bands are coded to indicate degree of resistance. </li></ul></ul>
    98. 98. Figure 39-24 This figure shows a resistor color-code interpretation.
    99. 99. Figure 39-25 A typical carbon resistor.
    100. 100. Resistors <ul><li>Variable Resistors </li></ul><ul><ul><li>Two types of mechanically operated variable resistors used in vehicles. </li></ul></ul><ul><ul><li>Potentiometer: three-terminal variable resistor. </li></ul></ul><ul><ul><ul><li>Wiper contact provides a variable voltage output. </li></ul></ul></ul><ul><ul><ul><li>Used in throttle position (TP) sensors, sound system controls. </li></ul></ul></ul>
    101. 101. Resistors <ul><li>Variable Resistors </li></ul><ul><ul><li>Rheostat: two-terminal unit. </li></ul></ul><ul><ul><ul><li>Current flows through movable arm. </li></ul></ul></ul><ul><ul><ul><li>Used in dash light dimmer control. </li></ul></ul></ul>
    102. 102. Figure 39-26 A three-wire variable resistor is called a potentiometer.
    103. 103. Figure 39-27 A two-wire variable resistor is called a rheostat.
    104. 104. FREQUENTLY ASKED QUESTION <ul><li>Is Water a Conductor? </li></ul><ul><ul><li>Pure water is an insulator; however, if anything is in the water, such as salt or dirt, then the water becomes conductive. Because it is difficult to keep it from becoming contaminated, water is usually thought of as being capable of conducting electricity, especially high-voltage household 110 or 220 volt outlets. </li></ul></ul>? BACK TO PRESENTATION
    105. 105. FREQUENTLY ASKED QUESTION <ul><li>Why Is Gold Used if Copper Has Lower Resistance? </li></ul><ul><ul><li>Copper is used for most automotive electrical components and wiring because it has low resistance and is reasonably priced. Gold is used in airbag connections and sensors because it does not corrode. Gold can be buried for hundreds of years and when dug up it is just as shiny as ever. </li></ul></ul>BACK TO PRESENTATION ?

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