Electrical Resistance

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  • Created by: Clare
  • Created on: 28-03-13 14:05
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  • Electrical Resistance
    • Voltage
      • Current varies in PROPORTION to voltage
        • In a metal wire when it doesn't get hot
      • When voltage is connected across a wire, current flows through the wire
      • Different wires allow for different sized currents to flow for a given voltage
    • Resistance
      • Measured in Ohms
      • Voltage= current x resistance
    • Uses of resistors
      • Variable resistors allow you to change the amount of resistance using a rotary or sliding action
      • Lamp dimmer circuits
      • Volume control in audio equipment
      • Speed control in car games
    • Thermistors
      • Resistance decreases as temperature increases
        • Turn something ON in heat
      • Made from semi-conductors
      • Uses
        • Fire alarms
        • Turning on a fan/ cooling system
    • Light Dependent Resistors
      • Made from a semi-conductor
      • More light= less resistance
      • Uses
        • Light sensing cicuits
        • Turning on street lights at night
        • Automatic security lights
    • Diodes and LEDs
      • Only allow an electric current in the direction of the arrow
      • They have huge resistance in one direction and very low in the other
      • They are used as indicators to show when a device is turned on
      • Diodes are used in power supplies for DC equipment
    • Graphs
      • Resistance in a wire (Resistance- length)
      • Resistor (Current- voltage)
      • Bulb (Current- voltage)
      • Diode (current- voltage)
      • LDR (resistance- light)
      • Thermistor (Resistance- temperature)


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