Magnetism

• Electromotive force


  Also known as potential difference
• Magnetism


  A physics phenomenon created by moving charge
• Types of magnets


  • Permanent magnets
  • Electromagnets
• Electric fields


  Created by static (not moving) charged objects
• Magnetic fields


  Created by moving charges
• Classical physics magnetism models

  • Fundamental property that creates magnetism is electrons spin
  • Quantum physics envisions electron having qualities between a particle and wave
• Dipoles


  Two poles, north and south, created by a spinning electron
• Electrons spinning clockwise or counter clockwise have reverse north and south dipoles
• Pairing magnetic dipoles


  • North poles and south poles are attracted to each other
  • Pairing means the north pole of one is next to the south pole of the other
  • Electron pairing neutralizes magnetic properties created by an individual electron spin
• Magnetic attraction and repulsion

  • Opposite poles attract
  • Same poles repel
• Ferromagnetic materials


  • Electrons spin the same direction called domains
  • Domains maintain the dipole, north and south, and of the similarly spinning electrons
• Ferromagnetic elements


  • Iron
  • Cobalt
  • Nickel
• Magnetic alloys


  • Steel magnets (iron and carbon)
  • Neodymium magnets (neodymium, iron, and boron)
• Soft ferromagnetic metals


  • Do not easily remain magnetized
  • Domains become unaligned, losing magnetism when a magnetic field is removed
• Hard ferromagnetic metals


  • Keep domains aligned after a magnetic field is removed
• Induced or temporary magnet

  • Created when a "soft" ferromagnetic material is in the presence of an external magnetic field
  • Domains align and that object becomes an induced temporary magnet
  • Magnetism is easily lost when the external magnetic field is removed
• Permanent magnet


  • A "hard" ferromagnetic material is placed in a strong magnetic field
  • Domains align with a magnetic field and maintain that alignment after the magnetic field is removed
• Ways to demagnetize a magnet


  1. Heating a magnet

  2. Dropping or hitting the magnet
• Breaking a permanent magnet creates two weaker magnets with the same dipole alignment
• Compass


  • A magnet that is free to rotate when interacting with a magnetic field
  • The earth itself acts like a magnet believed to be caused by current in its outer core
• Earth's geographic north pole

  Unchanging location where the earth's surface intersects its north rotational axis
• Earth's magnetic north

  Location where a compass north, if held directly above it, would point directly down
• Earth's magnetic field creates a similar pattern as a large bar magnet with the magnetic south pole facing upwards
• Magnetic declination


  Angle difference from where the compass says is north and geographic north
• A current carrying wire produces its own magnetic field around it, with the direction determined by Fleming's left hand rule (thumb points along the current, fingers curl round the wire).
• When two magnets are brought together, they experience a force of attraction or repulsion depending on their poles.
• The magnetic field lines are always perpendicular to the direction of the force on a moving charge.
• The strength of the magnetic field decreases with distance from the source.
• The strength of this interaction depends on the distance between them and the relative orientation of their fields.
• Like poles repel, unlike poles attract.
• The magnetic field lines show the direction of the force on a positive charge placed at that position.
• Magnets can be made out of any ferromagnetic material such as iron, nickel, cobalt, gadolinium, dysprosium, terbium, holmium, erbium, thulium, yttrium, scandium, and praseodymium.
• The magnetic field can be represented using field lines that show the direction and magnitude of the field at different locations.
• The magnetic field lines form closed loops around a permanent magnet.
• The magnetic field lines are strongest near the surface of the magnet and weaken further away.
• The magnetic field lines form closed loops around a permanent magnet, indicating the presence of both a North and South Pole.
• The magnetic field lines are strongest near the surface of the magnet and weaken further away.
• Electric charges can be used as sources of electric fields, which exert forces on other charged objects.
• Magnets can also produce magnetic fields that interact with other magnets or charged particles.
• The strength of these interactions depends on factors such as the distance between the objects and the relative orientations of their fields.