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Electronics Technology Fundamentals

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Title: Electronics Technology Fundamentals


1
Electronics Technology Fundamentals
Lindem 11. jan 09
  • Chapter 1
  • Principles of Electricity

2
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

3
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

4
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

5
1.1 The Starting Point Elements, Atoms and
Charge P7
Det enslige elektronet i ytterste skall er
svakt bunnet til kjernen. Ved normal temperatur
har vi ca 1 fritt elektron pr. atom - ca 1023
elektroner / cm3 Figuren viser et kopperatom.
6
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

7
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.
8
1.2 Current P4
  • Electron Flow Versus Conventional Current

Insert Figure 1.10
9
1.2 Current P5
Direct Current - DC Versus Alternating Current -
AC
  • Direct Current (dc) unidirectional
  • Alternating Current (ac) - bidirectional

10
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.

11
1.4 Resistance and Conductance P1 - Motstand
og ledningsevne
  • 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
Tradisjonelt bruker vi ofte U som betegnelse for
spenning. Boka har imidlertid konsekvent valgt å
benytte V ( U R I )
12
1.4 Resistance and Conductance P2 - Motstand
og ledningsevne
  • Conductance ( Ledningsevne ) a measure of the
    ease which current will pass through a
    component
  • Unit of Conductance siemens (S)

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

13
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

14
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)

15
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

? resistivity (greek letter, rho) l
length A cross-sectional area
  • ExampleCalculate the resistance of a 25 cm
    length of copper that has a cross-sectional area
    of 0.04 cm2.

16
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

End 1.
17
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