CHAPTER TWO

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CHAPTER TWO

• Electrical Quantities and Components

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CONDUCTANCE

• Definition Ability to allow current to flow
• Relationship to Resistance Opposite of
  resistance
• Unit of measure Siemens

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ELECTRICAL UNITS AND ABBREVIATIONS

• Unit Measure Symbol
• Potential Volt V
• Current Ampere A
• Resistance Ohm ?
• Conductance Siemens S

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FAMILIAR METRICS
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CONDUCTORS

• Function
• to carry electrical energy from one point to
  another
• provide a path for electrical current flow
  between components or circuits
• Numerous types of conductors
• type to use determined by
• nature of application
• amount of electrical energy it must carry

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CONDUCTORS

• Ways of classifying conductors include
• type of metal used
• size of the wire itself
• form of the wire (solid, stranded, or braided)
• number of conductors used
• insulation characteristics

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SUPERCONDUCTIVITY

• All conductors have some resistance at normal
  operating temperatures
• Superconductivity current flow through a
  material with nearly zero resistance
• Only occurs in certain materials
• Only occurs at extremely cold temperatures (e.g.,
  273C)

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SUPERCONDUCTIVITY

• Certain ceramic materials have very low
  resistance at temperatures much higher than
  absolute zero (273C).
• low resistance at higher temperatures makes it
  easier to take advantage of superconductivity
• Some future possibilities
• more efficient motors, generators, and so on
• faster computers.

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PHYSICAL FACTORS OF CONDUCTORS

• Factors that influence resistance
• type of material
• length of conductor
• cross-sectional area of wire
• temperature of wire
• temperature coefficients

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PHYSICAL FACTORS OF CONDUCTORS

• Resistivity
• resistance in ohms of a given material per
  standard length (meters or mils) and
  cross-sectional area (square meters or circular
  mils)
• different materials have different resistivity
  characteristics

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CHARACTERISTICS OF WIRE

• Wire size and gauge
• Types and common usage
• stranded
• solid
• Current-handling capabilities and gauge

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RESISTORS

• Definition, Purpose, Types

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CHIP RESISTORS

• Resistors in high-density circuits

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RESISTOR SIZE

• The physical size of the resistor determines its
  ability to handle heat
• The difference between a chip resistor and a
  wire-wound resistor is merely its ability to
  handle current flow

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COMMON RESISTOR TYPES

• Fixed Resistors
• one value only
• common values available
• value determined by color coding
• variety of wattage rating
• quality ratings vary widely

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VARIABLE RESISTORS

• Potentiometer
• variable from 0 Ohms to labeled value
• popular due to flexibility
• found in use as volume controls
• physical sizes available vary widely
• resistance values vary widely
• resistance value generally stamped

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RESISTOR TYPE SUMMARY

• Wire-wound high wattage
• Potentiometer variable resistance values
• Rheostat alternative to potentiometer
• Chip resistor small size, commonly found
• Carbon composition fixed value, inexpensive

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THE RESISTOR COLOR CODE

• Purpose Indicate value efficiently
• Values Standard values available
• Color bands Three used to indicate value
• Tolerance Fourth band to indicate
  acceptable variance

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EXAMPLE COLOR CODING
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RESISTOR TOLERANCE

• Definition The range of acceptable values
• Common tolerance values 20, 10, 5
• Fourth band used to indicate tolerance

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EXAMPLE OF TOLERANCE

• Resistor colors Brown, Black, Brown, Gold
• Brown, Black, Brown 100 Ohms
• Gold /-5
• Upper Limit 105 Ohms
• Lower Limit 95 Ohms

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TYPICAL METERS
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MEASURING VOLTAGE WITH METERS

• Check Meter Settings
• function and range
• Meter Leads
• Red, positive ()
• Black, common ()
• Connection to circuit
• Displays normal and OL or OVL

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MEASURING RESISTANCE WITH METERS

• Remove power source
• Observe meter settings function and range
• Meter leads used like voltmeter
• Connection made across two points
• Precautions Power must be OFF

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MEASURING CURRENT WITH METERS

• Remove power source
• Observe meter settings Change position of the
  Red lead for most meters
• Connection to circuit via a break in the
  circuit
• Precaution Connection to circuit is critical!

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SCHEMATIC SYMBOLS

• Voltmeter
• Ohmmeter
• Ammeter

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THE SCHEMATIC DIAGRAM

• Wiring conventions Connection/no
  connection
• The switch Basic On/Off
• The resistor Fixed and Variable

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THE CIRCUIT