GENPHY MAGNETISM

• Magnetism


  Magnetic phenomena first observed at least 2500 years ago in fragments of magnetized iron ore
• Permanent magnets


  • Exert forces on each other as well as on pieces of iron that were not magnetized
  • When an iron rod is brought in contact with a natural magnet, the rod also becomes magnetized
  • When floated on water or suspended by a string from its center, tend to line up in a north-south direction

  
• Magnetic poles


  • One end of a bar magnet is a north pole (N pole), the other end is a south pole (S pole)
  • Opposite poles attract each other, and like poles repel each other
• Magnetic declination or magnetic variation

  The earth's magnetic axis is not quite parallel to its geographic axis, so a compass reading deviates somewhat from geographic north
• Magnetic inclination


  The magnetic field angled up or down on the earth's surface, at the magnetic poles the magnetic field is vertical
• Magnetic lines


  • Show the direction that a compass would point at each location
  • The direction of the field at any point can be defined as the direction of the force that the field would exert on a magnetic north pole
• There is no such thing as magnetic monopole or isolated magnetic pole, they always appear in pairs
• Magnetic field lines


  • The direction of the magnetic field is tangent to the field line at any point in space
  • The strength of the field is proportional to the closeness of the lines
  • Magnetic field lines can never cross
  • Magnetic field lines are continuous, forming closed loops without a beginning or end
  • The north and south poles cannot be separated

  
• Motion of charged particle in a magnetic field

  • Magnetic force is always perpendicular to velocity, so that it does no work on the charged particle
  • The particle's kinetic energy and speed thus remain constant
  • The direction of motion is affected but not the speed
• Magnetic forces on current

  • A current-carrying wire produces circular loops of magnetic field
  • To determine the direction of the magnetic field generated from a wire, use the right-hand rule (RHR-2)