Deck ni p6

• Magnets


  Certain stones that would attract and magnetize iron
• History of Magnets


  1. Ancient Chinese and Greeks discovered that certain stones would attract and magnetize iron

  2. Small slivers of the stone were found to align themselves with the North Pole

  3. Chinese were the first to use magnets for navigation

  4. The orienting properties were used to align streets in cities in the North-South / East-West direction
• Poles of a Magnet

  • Magnets have a North and South Pole
  • Like poles repel
  • Unlike poles attract
  • If you break a magnet in half, you will not get two monopoles
• Magnets either attract or repel each other
• South poles are attracted to north poles
• Like poles repel
• Unlike poles attract
• Bringing a compass near a bar magnet

  The north indicator of the compass will point toward the south pole of the magnet
• A compass points north because it is lining up with the earth's magnetic poles
• The Earth's Magnetic Field


  • The earth has a magnetic field that scientist believe is a result of the dynamo effect due to electrical currents created in the molten iron and nickel outer core
  • The magnetic field can completely flip, with the north and south poles swapping places
  • These reversals are unpredictable and come at irregular intervals averaging about 300,000 years
  • The last one was 780,000 years ago
• The magnetic North Pole is responsible for the aurora borealis
• The aurora australis occurs at the South Pole
• Source of Magnetic Fields

  Electrical charge in motion
• Magnetic Domains


  Groups of atoms with aligned poles
• Magnets can be temporary or permanent
• Soft Ferromagnetic Materials


  • Align their domains in the presence of an external magnetic field, creating a magnetic dipole
  • When the magnetic field is removed, the domains re-randomize resulting in no magnetic attraction
  • Soft ferromagnetic material is attracted to both the North pole and South pole
• Types of Magnets


  • Temporary (Electromagnets)
  • Permanent (Speakers)
• Permanent Magnet


  An object made from a material that is magnetized and creates its own persistent magnetic field
• Magnetic Metals


  • Nickel
  • Iron
  • Cobalt
• Non-Magnetic Materials


  • Aluminum
  • Plastic
  • Glass
• Ferromagnetism


  A substance such as iron in which the magnetic moments of the atoms spontaneously line up with each other, making a large net magnetic moment
• Ferromagnets lose their ferromagnetism when heated above a specific temperature, because the thermal energy melts the magnetic alignment
• Speakers


  • Consist of a permanent magnet surrounding an electromagnet that is attached to the loudspeaker membrane or cone
  • By varying the electric current through the wires around the electromagnet, the speaker cone moves back and forth, creating sound waves
• Maglev Trains


  Vehicles that "float" over an electromagnetically powered fixed steel guideway and are propelled by the current with no motors, wheels, moving parts or additional energy sources
• Applications of Magnetism


  • Computer disc drives (hard and floppy)
  • VCR and cassette tape
  • Credit cards
  • Speakers
  • Motors (Both AC and DC)
  • Speed sensors
  • Solenoids for relays, valves, etc.
  • Magnetos (piston engine aircraft)
• Key Ideas


  • All magnets have North and South Poles
  • Magnetic field lines originate in the North and end at the south pole
  • Magnetic field lines do not cross
  • Magnetism exists at the atomic level
  • Magnetism is the result of moving charges
  • Some magnets are temporary while others are permanent
  • Types of Magnetism: Ferromagnetism, Paramagnetism, Diamagnetism