Magnetic Fields

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  • Created by: Jasmin
  • Created on: 06-05-13 14:37
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  • Magnetic Fields
    • A magnetic field is a region where magnetic materials (iron, steel) and also wires carrying currents experience a force acting on them
    • Arrows on field line always north to south
    • When current flows through a wire, magnetic field created around the wire
    • Thumb: current Fingers: magnetic field
    • An electromagnet is made of insulated wire wrapped around an iron bar (the core)
    • Magnetic field from wire magnetises iron bar
    • Current switched off, iron bar loses magnetism
    • Steel is unsuitable as keeps magnetism when current is switched off
    • Examples
      • Scrapyard crane: used for lifting steel and iron
        • Steel frame of vehicle sticks to electromagnet when current passes through coil
          • Current switched off, steel frame drops off electromagnet
      • Circuit breaker
        • Switch held in place by iron catch
          • Too much current, witch pulled open by electromagnet, switch opend
            • Stays open till reset manually
      • Electric bell
        • Bell connected to battery, iron aarmature pulled onto electromagnet
          • Opens the make - and - break switch and electromagnet switched off
            • Armature springs back and the make - and - break switch closes again
              • Cycle repeats itself
      • Relay - used to switch electric machine on/off
        • Current passes through electromagnet, armature pulled onto electromagnet
          • Armature turns about the pivot and closes the switch gap


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