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Lecture 13 2 26 2004
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Lecture 13 2 26 2004


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  • 1. Magnetism
    Similar to electric forces
    Magnetic Poles
    North and South Poles
    Historic Designations
    Like Poles Repel, Unlike Poles Attract
    Due to alignment of atoms in material
  • 2. Magnetic Fields
    Similar to electric and gravitational fields
    Magnetic fields are produced by the MOTION of electric charges
  • 3. Magnetic Fields
    Revolving electron produces field
    Spinning electron produces field
    In most atoms, combination of spins and orbits are in opposite directions
    The fields cancel each other out
    Some atoms, they don’t cancel
    Iron, nickel, cobalt, aluminum
  • 4. Magnetic Domains
    In iron, for example, field by an atom is so strong it causes neighboring atoms to arrange their spins and orbits to line up
    These clusters form magnetic domains
    Domains are randomly oriented in ordinary iron, nickel, etc.
    Can force them to line up with external field
  • 5. Electric Currents & Magnetism
    A moving charge produces a magnetic field
  • 6. Electric Currents & Magnetism
  • 7. Electromagnetics
    Place a piece of unmagnetized iron in a coil of wire carrying a current
    Produce a strong magnetic field in the iron by lining up domains
    Makes the whole thing a very powerful magnet
  • 8. Magnetic Forces and Charges
    If a charge isn’t moving, a magnetic field has no effect on the charge
    Reciprocal kind of idea
    Moving charges produce magnetic fields
    Magnetic fields apply a force to a moving charge
  • 9. Magnetic Forces and Charges
  • 10. Magnetic Forces and Charges
  • 11. Magnetic Forces and Charges
  • 12. Meters
    Use a compass needle (magnet)
  • 13. Meters
  • 14. Motors
  • 15. Electromagnetic Induction
  • 16. Electromagnetic Induction
  • 17. Electromagnetic Induction
  • 18. Electromagnetic Induction
  • 19. Electromagnetic Induction
    Faraday’s Law
    The induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loops.
    The amount of current depends on the resistance of the wire
    Changing magnetic field in a loop is key!!
  • 20. Electromagnetic Induction
    Traffic light control (buried loops)
    Airport Security Systems
    Mag strips on credit cards
    Tape Recorders
    Computer Hard Drives
  • 21. Generators
  • 22. Generators
  • 23. Power Production
  • 24. Transformers
  • 25. Transformers
    The more turns, the more voltage induced
    Step-up Transformer has more turns in secondary than in primary
    Step-down Transformer has more turns in primary than in secondar
  • 26. Transformers
    Energy Conservation
    Power In = Power Out
  • 27. Field Induction
    An electric field is induced in any region of space in which a magnetic field is changing with time
    A magnetic field is induced in any region of space in which an electric field is changing with time
    “Let there be light!!!”