ELECTRICITY MODULES Through Cognitive Learning

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ELECTRICITY MODULES(Through Cognitive Learning)

• ENGINEERING TECHNOLOGY

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MODULE 2 - RESISTANCE

• Devices
• Atoms
• Insulators
• Conductors
• Resistors Potentiometer
• Equipment
• Lightning Rods
• Rubber Gloves
• Wooden Ladders

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The Elements

• All matter, however complex, living or nonliving,
  is some combination of the elements.
• Currently, 109 elements have been identified.
• Atoms are the smallest form of the elements.

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Periodic Table
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Electrical Charges

• The unit of electric charge is the coulomb.
• Over 6 billion billion (6.25 x 1018 protons) to
  have a charge of one coulomb!
• Electric charge is conserved. Charge can be
  transferred from one place to another, but it is
  not destroyed.

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Electric Charges

• Electric charges exert forces upon one another.
• Charges with same polarity repel.
• Charges with opposite polarity attract.

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Types of Electric Charge

• Positive
• protons
• Negative
• electrons
• Neutral Atoms have the same number of protons and
  electrons.

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Electric Properties

• Conductor
• Electrons in this material can flow with relative
  ease.
• Insulator (dielectric)
• Electrons in this material require very high
  voltage to dislodge

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Electron

• The electron is negatively charged.
• Charge of an electron 1.6 ? 10?19 coulomb
• Number of electrons in outer shell of atom
  dictate type of molecular bonding, chemical
  properties and physical properties of that atom.
• Naturally occurring atoms are electrically
  neutral so there must be positively charged
  particles that are also a part of an atom.
• J. J. Thompson proposed a plum pudding model.

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Thompsons Model
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Thompsons model

• Electrons are suspended like plums in a mixture
  of positively charged pudding.
• This model was rejected after experimentation
  with diffraction of particles.

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Rutherfords Experiment

• In 1909, Ernest Rutherford performed an
  experiment with energetic alpha particles
  striking gold foil.
• Found that most of the space within an atom is
  empty space.
• Most of the mass is contained within a small
  region called the nucleus.
• If a sphere having a diameter of 1 cm were packed
  at the density of the nucleus of an atom it would
  weigh 133,000,000 tons!

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Rutherfords experiment
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Protons and Neutrons

• The nucleus contains both neutral and positively
  charged particles
• Neutrons same size as protons but have no net
  charge.
• Protons positively charged particles having
  approximately 1800 times the mass of an electron.

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Protons and Neutrons

• Atomic number the number of protons in an atom.
• All atoms with the same atomic number have the
  same chemical properties.
• Isotope atoms with the same atomic number but
  differing numbers of neutrons.
• Atomic mass or Mass number the total number of
  particles contained in a nucleus, (protons plus
  neutrons).

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Bohrs model of the atom

• In 1911 Niels Bohr proposed a model in which
  electrons orbited the nucleus in circular orbits
  called energy shells.
• Electrons in different orbits contain different
  amounts of energy.

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Bohrs model
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Electricity Conductors

• Conductors are materials which have free
  electrons - typical conductors are ___
• Electricity is the flow of ________
• Electrons are ________ charged particles
• Electrons are attracted to a _____ charge
• A Coulomb of charge is to 6.242 x 1018
  electrons
• The current is the charge in Coulombs passing a
  point in a precise time.

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Superconductivity

• In certain materials as temperature is lowered to
  a critical temperature, R 0? i.e. zero
  resistance to current flow.
• Zero resistance means no I2R heating losses
• applications
• transmission lines
• electrical energy storage
• magnetic levitation

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Superconductivity

• Until recently, very low temperatures were
  required, lt 20? K
• In 1987, discovery of superconductivity in
  yttrium-barium-copper oxide at gt100 ? K resulted
  in liquid nitrogen being used as a coolant.
• Goal is a room temperature superconductor.

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Resistance

• Resistance opposition to the flow of electrons
  through a material.
• Defined with the following formula R
  ? l /A
• ? resistivity of material
• l length
• A cross sectional area

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Ohms Law

• I V/R
• V I?R
• Conductors that exhibit zero resistance under
  certain conditions are called superconductors.

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Ohms Law

• The current flowing through a circuit is directly
  proportional to the potential difference and
  inversely proportional to the resistance.
• Resistance is a property of the type and size of
  the material through which the current is
  flowing. (Compare to R-value in heat transfer)
• The unit of resistance is the ohm (?).