Electronics

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Electronics Computer Organization

• Electricity

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Negative and Positive Polarities

• Polarity is the condition of being negative or
  positive.
• The electron is the smallest amount of electric
  charge having the characteristic called negative
  polarity.
• The proton is the basic particle with positive
  polarity.

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Electricity

• Electricity is a form of energy associated with
  electric charges.
• The arrangement of electrons and protons as basic
  particles of electricity determines the
  electrical characteristics of all substances.

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Electrons Protons in the Atom

• Electrons and protons assemble in specific
  combinations for a stable arrangement.
• Each stable combination of electrons and protons
  make one particular type of atom.
• An atom is the smallest particle of the basic
  elements which forms the physical substances we
  know as solids, liquids, and gases.

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Parts of an Atom
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Parts of an Atom

• The nucleus is the central mass of an atom.
• The number of protons in the nucleus determines
  the atomic number which distinguishes one element
  from another.
• The total number of protons and neutrons
  determines the atomic weight.
• Electrons are negligible because its weight is
  merely 1/1845 of a proton.

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Orbital Shells
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Orbital Shells

• The outer shell is called the valence shell, and
  the number of electrons it contains is the
  valence.
• Conductivity of an atom depends on its valence
  band.
• Conductivity of a material is its ability to
  allow the free flow of electricity.

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Conductivity

• Conductors are materials that contain a large
  number of free electrons. They allow the free
  flow of electricity.
• Insulators are materials that do not contain free
  electrons. They prevent the flow of electricity.
• Semi-conductors are neither good conductors nor
  good insulators.

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The Coulomb Unit of Electric Charge

• Named after Charles A. Coulomb, a French
  physicist (1736-1806) who measured the force
  between charges.
• 1 coulomb (C) is equal to the charge of 6.25 x
  1018 electrons.
• 1 electron has a negative charge with a magnitude
  of 0.16 x 10-18.

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Physical Force Between Charges

• Opposite charges attract
• Like charges repel

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The Volt Unit of Potential Difference

• Named after Alessandro Volta (1745-1827), Italian
  physicist who developed the first chemical
  battery.
• 1 volt (V) is the measure of the amount of work
  or energy needed to move an electric charge.
• 1 Joule (J) of energy is expended in moving 1 C
  of charge between two points.

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Charge in Motion

• When potential difference between two charges
  forces a third charge to move, the charge in
  motion is an electric current.
• Potential difference is necessary to produce
  current.

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The Ampere Unit of Current

• Named after Andre Ampere (1775-1836), French
  physicist who discovered that two parallel wires
  attract when currents flow through them in the
  same direction and repel when otherwise.
• 1 ampere (A) is the rate of electron flow if 6.25
  x 1018 electrons flow past a point per second.

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The Ohm Unit of Resistance

• Named after Georg Simon Ohm, a German physicist
  who developed what is now known as the Ohms Law
  (1787-1854).
• Resistance is the opposition to current.
• Conductors have very little resistance
  insulators have large amounts of resistance.

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The Ohm Unit of Resistance

• 1 ohm (O) is the resistance that develops 0.24
  calorie of heat when a current of 1A flows
  through a given material for 1 second.

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The Siemens Unit of Conductance

• Named after Ernst von Siemens, a German inventor
  (1816-1892).
• Conductance (G) is the opposite of resistance.
• The old unit name is the mho, which is ohm
  spelled backwards.
• G is the reciprocal of R.

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The Closed Circuit

• A circuit can be defined as a path for current
  flow.
• A closed circuit provides an unbroken path for
  current flow.

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3 Important Characteristics

• There must be a source of V. Without v, I cannot
  flow.
• There must be a complete path for current flow,
  from one side of the v through the external
  circuit, and returning to the other side of the
  same v.
• The current path normally has R. The R generates
  heat or limits I.

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The Direction of Current Flow

• Electron flow, from point of negative potential
  to point of positive potential.
• Conventional current, the motion of positive
  charges from area of higher potential to area of
  lower potential.
• Electrical engineers use conventional current
  flow, electronic technicians use electron flow.

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AC/DC

• DC is unidirectional because the voltage source
  maintains the same polarity of output voltage.
• AC periodically reverses or alternates polarity.

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Comparison of AC/DC

• Fixed Polarity
• Can be steady or vary in magnitude
• Steady value cannot be stepped up or down
• Terminal voltages for transistor amplifiers
• Easier to measure

• Reverses in polarity
• Varies between reversals in polarity
• Can be stepped up or down with transformer
• Signal input and output for amplifiers
• Easier to amplify

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Sources of Electricity

• Static Electricity by Friction
• Conversion of Chemical Energy
• Electromagnetism
• Photoelectricity

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End of Lecture

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