Electronics Technology Fundamentals

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Electronics Technology Fundamentals
Lindem 14 jan.07

• Chapter 1
• Principles of Electricity

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1.1 The Starting Point

• Atomic Structure
• Atom smallest particle of matter that retains
  the physical characteristics of an element
• Bohr Model
• Simplest model of an atom
• Central core (nucleus) contains protons and
  neutrons
• Electrons revolve around nucleus

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1.1 The Starting Point Elements, Atoms and
Charge P3

• Atomic Structure (Continued)
• Atomic Number of an Atom number of protons
• Atoms contain an equal number of protons and
  electrons
• Electrons travel in orbital paths (shells)
• Valence Shell
• Outermost shell
• Cannot hold more than eight electrons
• Complete shell contains eight electrons

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1.1 The Starting Point Elements, Atoms and
Charge P6

• Attraction and Repulsion - Like charges repel
  each other and opposite charges attract each
  other
• Ions
• Outside force can cause an electron to leave its
  orbit -atom is referred to as a positive ion
• Outside force can cause an atom to gain an
  electron -atom is referred to as a negative ion
• Free Electrons
• An electron that is not bound to any particular
  atom
• Can neutralize a positive ion

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1.1 The Starting Point Elements, Atoms and
Charge P7
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1.2 Current P1 Elektrisk strøm

• Current the directed flow of charge through a
  conductor
• Thermal energy (heat) is sufficient to free
  electrons in copper
• Free electron motion is random unless outside
  force is applied

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1.2 Current P2 Elektrisk strøm

• Represented by the letter I (for intensity)
• Measured in charge per unit time

• Coulomb (C) represents the total charge of
  approximately 6.25 x 1018 electrons
• Unit of Current Ampere (A) 1 coulomb/second

3 coulombs of charge pass a point in a wire every
two seconds. Calculate current.
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1.2 Current P4

• Electron Flow Versus Conventional Current

Insert Figure 1.10
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1.2 Current P5
Direct Current Versus Alternating Current

• Direct Current (dc) unidirectional

• Alternating Current (ac) - bidirectional

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1.3 Voltage P1

• Voltage a difference of potential that
  generates the directed flow of charge (current)
  through a circuit

• Often referred to as electromotive force (EMF)
• Unit of Voltage volt (V) 1 joule/coulomb
• Volt the difference of potential that uses one
  joule of energy to move one coulomb of charge.

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1.4 Resistance and Conductance P1

• Resistance opposition to current
• Unit of Resistance ohm (? - Greek letter omega)
• Ohm the amount of resistance the limits current
  to one ampere when one volt is applied

Ohms lov U R I
Insert Figure 1.13
Denne læreboka skiller ikke mellom U og V
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1.4 Resistance and Conductance P2

• Conductance ( Ledningsevne ) a measure of the
  ease which current will pass through a
  component
• Unit of Conductance siemens (S)
• Old Unit of Conductance mhos (upside down
  omega symbol)

where G conductance R resistance
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1.4 Resistance and Conductance P3

• Examples1. Calculate the conductance of a 10 K?
  resistor.
• 2. Calculate the resistance of a circuit that has
  a conductance of 25 mS.

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1.5 Conductors, Insulators and Semiconductors P1

• Conductors materials that provide little
  opposition to the flow of charge (current)
• Example copper
• Few valence shell electrons, one valence shell
  electron per atom makes the best conductor
• Insulators materials that normally block
  current
• Example rubber
• Complete valence shell

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1.5 Conductors, Insulators and Semiconductors P2

• Semiconductors materials that are neither good
  conductors nor good insulators
• Example graphite (used to make resistors)
• Half-complete valence shells (four valence
  electrons)

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1.5 Conductors, Insulators and Semiconductors P3

• Other Factors that Affect Resistance
• Resistivity the resistance of a specified
  volume of an element or compound
• CM-?/ft Circular-mil ohms per foot
• ?-cm Ohm-centimeters
• Length
• Cross-Sectional Area

where ? resistivity (greek letter, rho) l
length A cross-sectional area
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1.5 Conductors, Insulators and Semiconductors P5

• ExampleCalculate the resistance of a 25 cm
  length of copper that has a cross-sectional area
  of 0.04 cm2.

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1.5 Conductors, Insulators and Semiconductors P6

• The Effects of Temperature on Resistance
• Positive Temperature Coefficient
• Resistance increases as temperature increases and
  vice versa
• Example most conductors
• Negative Temperature Coefficient
• Resistance decreases as temperature increases and
  vice versa
• Example most semiconductors and insulators

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Fargekode for motstander
End 1.