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NUE 052 - Electrical Characteristics of Materials

Electric Charge

An electron is the smallest known particle that can hold an electric charge
  • Electrons are part of an atom
  • Atoms cannot be seen without using a special instrument known as an electron microscope
  • At the center of an atom is the nucleus which is made up of positively charged protons and neutrons which have no charge
  • Electrons are negatively charged and orbit the nucleus
  • Elements such as Copper have 29 atoms, where Hydrogen has just one
  • Each element has different types of atoms; e.g., Copper atoms are different to those of Hydrogen
  • All materials can be classified as having the electrical properties of conductor, insulator or semiconductor
  • Copper is a good conductor that shows little resistance to electron flow
  • A voltage is always present between two points with a different number of electrons
  • Electron flow is greater in materials that that are good conductors.
  • Conductors, Insulators and Semiconductors

    Conductors are mostly metals such as silver, gold, copper and aluminium
  • A conductor has less resistance to electron flow than insulators
  • Insulators are materials that prohibit the flow of electrons unless the voltage is high enough to break down the insulator and allow electron flow
  • Semiconductors are neither conductors or Semiconductors are treated with a chemical (doped) to give it special properties
  • Conductor
    Insulator and Breakdown Voltage
    Mica - 2,000V
    Glass - 900V
    Paper - 500V
    Rubber - 275V

    Electric Current

    Current is the flow of electrons from a point where there are more electrons to a point where there are less electrons
  • For current to flow a voltage must be present
  • Electron flow is from negative where there is an excess of electrons, to positive where there are less electrons
  • However electricians refer to current flow as positive to negative
  • This is called conventional current flow
  • Electric current is measured in Amps
  • The symbol for current is the letter A
  • In an electric circuit current does the work and voltage cause the current flow
  • Electromotive Force

    The voltage from a voltage source such as a battery is also known as electromotive force or EMF
  • The symbol for EMF is the letter E
  • Voltage or EMF measured between two points is also known as electrical pressure
  • Practice Tests are available on the practice test page  
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