Resistance and resistivity

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  • Created by: Sevdeg
  • Created on: 12-05-14 07:51
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  • Resistance and resistivity
    • I-V graph for a resistor: Straight line passing through the origin. I is directly proportional to V.
      • Resistance= 1/ Gradient of the graph
    • Ohm's law: For a metallic conductor at constant temp. the current is directly proportional to the PD.
    • LED and semi conductor diodes are non ohmic materials.
    • I-V characteristics for a filament lamp: Line passes through origin. At higher voltages line starts to curve.
    • Thermistors are made from metal oxides. There are two types of thermistors:
      • 1. NTC: Resistance decreases with increasing temperature.
      • 2. PTC: Resistance rises suddenly at a definite temperature.
    • 2 factors affect the resistance of a metal: the temperature and impurities
    • Resistance is proportional to length and inversely proportional to area.
      • Resistivity: RA/L
        • Resistivity increases with temp because there are more frequent collisions between electrons and ions.

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